These are among the most important of the household pests. In a survey of 8 large housing projects in North Carolina, 2 in each of 4 cities, cockroaches were found in 76.7% of the apartments in which control work was done by project maintenance men and in 12.7% of those that were regularly treated by licensed pest control operators (Wright, 1965a). Cockroaches are also known to cause severe injury to plants and their fruits, particularly in greenhouses (Roth and Willis, 1960).
This group of insects is well known to biology students because, like grasshoppers, they are commonly chosen for laboratory demonstrations of a somewhat generalized type of external and internal insect morphology. They are also commonly reared for research purposes, e.g., as test insects in the investigation of new insecticides. Nearly every entomological research group continuously maintains a culture of 1 or more species of cockroaches.
It is fortunate that during the last decade, insects of such great importance as the cockroaches, not only as pests, but also as experimental animals in teaching and research, have become the subjects of some excellent books containing a wealth of information of both academic and practical importance.In The Biology of the Cockroach (Guthrie and Tindall, 1968), one chapter deals with insecticides and control. Likewise, The Cockroach (Cornwell, 1968) has thus far appeared as Volume I which contains "An account of the biology oi the more common species, including details of their structure, physiology, behavior, and ecology." Volume II is expected to be published in 1975, and will be devoted to cockroach control methods. It should be available by the time our present book has been completed.
Mastotermes darwiniensis has an egg mass similar in appearance to the egg capsule (oötheca) of cockroaches. Its eggs are firmly cemented together by a light-brown, gelatinous secretion that fills the interstices (Hill, 1925; Snyder, 1935).
The ability many cockroaches have to mix bits of debris with mouth secretions in order to hide or disguise their oöthecae reminds one of a similar process used by termites to build nests. There are other interesting similarities (Rau, 1941; McKittrick, 1964, 1965; Cornwell, 1968).
Cryptocercus punctulatus leads a subsocial life in decayed logs, which serve as both food and shelter (Snyder, 1935). An Australian cockroach, Panesthia, lives in distinct family groups in burrows in the soil. Each group consists of an adult male and a viviparous female, and from 10 to 20 nymphs in various instars. Soon after reaching maturity, the adults bite off their own tegmina and hindwings; wings are inconvenient for insects that inhabit burrows. This indicates the probable origin of termites' social life in subterranean galleries and their discarding of wings (Tillyard, 1926). The subsequent evolution of termite social organization to such an astounding degree of complexity, superficially so strikingly similar to that of the social Hymenoptera, depended on a concomitant chemical evolution of pheromones and a highly specialized chemical communication among these insects. This is a good example of the important role of pheromones in insect evolution.
The ancient cockroaches folded only a small area (anal lobe) of their hindwings, as can be seen in the fossil genus Pycnoblattina. The living Mastotermes darwiniensis also folds the anal lobe of its hindwings. The cockroaches gradually evolved more complex folding of the hindwings, while the termites, except for M. darwiniensis, completely lost this feature of their wing structure (Tillyard, 1936, 1937; McKittrick, 1964). McKittrick (1965) believed that cockroaches, walkingsticks, and termites belonged in the same insect order. She pointed out that Cryptocercus had xylophagous flagellates in common with primitive termites but not with other cockroaches. On the other hand, the primitive Mastotermes darwiniensis has intracellular bacteriocytes in common with cockroaches, but not with other termites. Also, in certain morphological features, Cryptocercus differs far less from Mastotermes than it does from many of the cockroaches.
One way in which cockroaches differ from the closely related grasshoppers, locusts, and crickets is that they do not have a visible ovipositor. Also, they do not lay their eggs singly or in pods, but in a hardened, purseshaped egg case called the oötheca (plural, oöthecae). Most domestic cockroaches drop their oötheca as soon as it is formed, but the German cockroach (Blattella germanica), generally the species most frequently found in the household, carries hers until a day or two before the eggs are ready to hatch. She is often seen with an attached oötheca (figure 148).
Among domiciliary cockroaches, B. germanica is the only species with an oötheca subject to desiccation. The eggs are dependent on moisture supplied by the mother. The oöthecae of other species are remarkably resistant to desiccation. Pryor (1940) believed the oötheca of Blatta orientalis to be covered with an oily secretion, probably derived from the cuticle of the mother. It was so effective in retarding water loss that eggs hatched in about 46 days from oöthecae that had been kept in an atmosphere of 0% relative humidity from the age of less than 1 day (Roth and Willis, 1955).
Oöthecae also effectively protect the enclosed eggs from insecticides. Not until the eggs are hatched and the nymphs leave the protection of the oötheca and crawl over the insecticide residue are they subjected to the effects of an insecticide treatment, provided the residue retains its efficacy that long.
The distribution of domiciliary cockroaches throughout the world was made possible by their ability to infest the various means of intra- and intercontinental transport, particularly ships. Originally, and probably to this day, their principal means of transportation between continents has been by ships. (Movie fans and readers of classics may be interested in the fact that in 1792, the much-maligned Captain Bligh combated cockroaches on HMS Bounty with boiling water.) However, transport of cockroaches in the baggage compartments and kitchens of aircraft has been abundantly documented (Roth and Willis, 1960).
For many years, the principal species infesting ships was the American cockroach, but in more recent times the German cockroach has become the dominant ship-infesting species (Cornwell, 1968).
To judge by the enormous numbers of cockroaches infesting ships before the advent of effective insecticides, these insects must have found abundant food and water. Even without food and water, however, cockroaches can live for considerable periods. Newly emerged adult females of the German cockroach, Blattella germanica, have been found to live at 27°C (81°F) and 36 to 40% relative humidity for an average of 20.1 days without food or water, 14.7 days with dry food (dog biscuits) and no water, 35.1 days with water but no food, and 82 days with both food and water. The corresponding figures for the American cockroach, Periplaneta americana, were 41.7, 40.1, 89.6, and 190 (Willis and Lewis, 1957). The apparent ability of the 2 species to survive slightly longer without food and water than with dry food alone is interesting, but in any case, cockroaches are well adapted to dispersal over great distances by man, even when food and water are lacking.
Domestic species of cockroaches never or rarely fly, but are readily carried about in and on such items as sacks, cartons, or packages (particularly corrugated cartons) of food, in laundry, or in kitchen appliances and furniture. Beverage cartons are particularly important means of distributing cockroaches. The cartons are often contaminated with spilled syrups or malts, which attract cockroaches. Empty and unrinsed softdrink or beer bottles in night clubs, restaurants, markets, and homes form a part of the infestation chain. More than 200 cockroach nymphs have been found in a single soft-drink bottle brought to a market for exchange (DeLong, 1962). Cockroaches may be found by the thousands in insulation in the walls of refrigerators and gas or electric ranges, surviving for months if necessary without access to their usual foods and feeding only on cast skins and dead insects. Cockroaches may become established in basements or crawl spaces, particularly, if these places are dark and damp, and they may then enter the building around utility pipes, air ducts or ventilators, or under doors.
Although cockroaches are nocturnal, if they are abundant a few of them may be seen during daylight hours, particularly if articles in pantries, cabinets, and closets are moved about to disturb their hiding places. Other evidences of a cockroach infestation may be dead cockroaches, cast skins of the various nymphal instars, empty egg cases, and fecal droppings. The droppings are variable in size, and range from as small as "flyspecks" to as large as mouse droppings. Intersections and corners of shelves and the hinges of cabinet, pantry, and even closet doors show fecal stains when there are heavy infestations. The musty odor left on objects cockroaches contact may also be evident in heavy infestations.
Parasitic toxoplasmosis is a disease that is believed to infect more than a third of all adult Americans at some time during their lives. It is usually a mild disease, but can be extremely serious in pregnant women, causing congenital defects in an unborn child while remaining mild or symptomless in the mother. The protozoan parasite, Toxoplasma, can be acquired by eating infected raw or undercooked meat. If the blood serum of an infected person is added to cultures of the parasites, the differing colors of fluorescence of the latter will indicate either a positive or negative reaction and thereby serve as a test for the disease (Anonymous, 1973a).
Cats that consume birds or rodents carrying the parasite can become carriers. Filth flies have been found capable of transmitting infectious Toxoplasma oöcysts to human food 1 or 2 days after consuming infected cat feces. In laboratory tests, Toxoplasma parasites were isolated from the digestive tracts and feces of cockroaches as long as 7 and 10 days, respectively, after the cockroaches had last been in contact with infected cat feces. Filth flies and cockroaches might consume infectious cat feces and contaminate human food. They might also serve as food for birds and small rodents that could in turn be eaten by cats (Anonymous, 1973a).
Goodwin (1973) recorded the successful passage of hepatitis B antigen (AB-Ag) through the alimentary tracts of American cockroaches, and identified the antigen in the feces of the insects. The hepatitis antigen was found in the feces of the cockroaches for up to 9 days after their initial exposure to the antigen-positive test meal.
In an investigation to test the age of onset of skin reactivity, 38 out of 102 allergic children, ranging from infants to 12 years old, gave positive cutaneous reactions to body extracts of the German cockroach, Blattella germanica, compared with only 5 out of 100 nonallergic children. A 4-year-old asthmatic child was the youngest to give a positive reaction (Bernton and Brown, 1970a). In a later investigation, it was found that an extract of B. germanica caused an attack of asthma in 10 asthmatic persons with skin hypersensitivity to the extract and other allergens, but not in asthmatics without such skin hypersensitivity (Bernton et al., 1972).
An allergen in the feces of B. germanica acts as an ingestant when it contaminates food and as an inhalant when dried fecal particles become incorporated with house dust (Bernton and Brown, 1970b).
Roth and Willis (1960) also stated that species from at least 6 families of Hymenoptera had been recorded as developing on cockroach eggs. They quoted Edmonds (1957) as stating that evaniid egg parasites were so abundant in a home in Ohio that the occupants considered them a nuisance, although the oriental cockroaches in the basement did not annoy them. Roth and Willis also listed many predators, including scorpions, spiders, dragonflies, mantids, bugs (e.g., reduviids), beetles (carabids, rhipiphorids [similar to mordellids], dermestids, and others), wasps, ants, toads, frogs, lizards, birds, poultry, and various mammals. Cannibalism among cockroaches, including the devouring of oöthecae, has been noted by many investigators even when food was adequate.
When humidity is too high in cockroach culture colonies, mites may become numerous, and have been known to cause German cockroaches to drop their oöthecae prematurely, resulting in a low percentage of eggs hatching. Control of mites with acaricides has been known to increase the vigor of cockroach colonies (Roth and Willis, 1960). A pterygosomid mite Pimeliaphilus podapolipophagus Trågårdh, must actually feed on live cockroaches to survive; it cannot subsist on feces, cast skins, or dead insects (Cunliffe, 1952). It has been accused of biting people, and its presence in homes is an indication of cockroach infestation (Baker et al., 1956).
Roth and Willis (1960) reported 2 species of spiders in the family Theridiidae, the South African Latrodectus indistinctus and the North American L. mactans, the latter the venomous "black widow," as predators of cockroaches. The author observed another theridiid spider, Steatoda grossa (C. L. Koch) (figure 212, chapter 9), which resembles the black widow but is one of its natural enemies, in great abundance in an infestation of German cockroaches confined to experimental mockup closets at the University of California (Los Angeles). Remains of cockroach nymphs were found in their webs. It is also of interest to note in this connection that the related S. fulva (Keyserling) blocks the nest entrances of the harvester ant Pogonomyrmex badius (Latreille) during the early afternoon, when temperatures are high and the ants are inactive, and feeds on the ensnared ants (Hölldobler, 1970). Steatoda albomaculata (De Geer) also feeds on ants (Levi, 1957).
From their extensive review of the literature, Roth and Willis (1960) concluded that with the exception of a few instances of egg parasitism such as just cited with respect to Comperia merceti and Tetrastichus hagenowii, there had been too little information to enable them to evaluate the effectiveness of biological control in reducing the numbers of pest cockroaches, and that further investigation would be justified.
A large percentage of any cockroach population generally contains internal parasites. Two species of nematodes and 7 of protozoan parasites were found in 105 Blattella germanica in New York city.
One of these nematode species, Blatticola blattae (Graeffe), was present in 96.2% of the cockroaches collected. Among the protozoa, Nephridiophaga blattellae was found in 82.8% of the cockroaches, and 3 other species were abundant (Tsai and Cahill, 1970).
It is important to prevent contamination of a colony by stray individuals of other species. It is especially important to keep German cockroaches out of colonies of other species because of the ability of this insect to thrive and rapidly increase its numbers at the expense of the others.
In the cockroach rearing room, boric acid powder applied under benches, radiators, appliances, cabinets, etc., will serve to permanently prevent a buildup of the cockroach population, in the rearing room and adjacent rooms, from those insects which escape when they are being removed for experimental work.
Twenty cans of German cockroaches and a can or more of each of the other 5 species are continuously maintained in our laboratory. The temperature is kept near 80° F (27° C) in the rearing room. Provided that a water supply is constantly maintained, the author and his colleagues have had no indication that the maintenance of relative humidity above ambient is of any advantage in the rearing of cockroaches, at least in the rearing cans just described. With ambient humidity and monthly removal of the debris at the bottoms of the cans (with a vacuum-cleaner device), infestation of German cockroaches by parasitic mites has been avoided. American cockroaches drop their egg cases to the bottoms of their rearing cans; therefore, the cans are vacuumed only about twice a year, but their colonies do not produce so much debris and do not seem to be so susceptible to mite infestation as those of the German cockroaches.
Description. Adult German cockroaches are 1.3 to 1.6 cm long, pale brown or tan, and have 2 parallel dark streaks on the pronotum (plate III, 1). They have chewing mouthparts. (See figures 44and 45, chapter 4, showing the similar American cockroach.) Their movements are very rapid when they are disturbed. They are nocturnal. If a few are seen crawling about in open spaces during daylight hours, this indicates that the infestation is already severe. The female is darker and has a broader abdomen than the male, and is rounded posteriorly. If German cockroaches are placed on their backs, the males are easily distinguished by the yellowish, slender abdomen, tapering gradually to the posterior end. The abdominal cerci of the males have 11 segments and those of the females have 12.
In their investigation of the German cockroach, Willis et al. (1958) found the ratio of females to males to be 1.12:1. In similar work, Ross (1929) observed that the sexes occurred in approximately equal numbers.
Mating Behavior. Roth and Willis (1952) determined that the male of the German cockroach could not detect the female from a distance, even when in close proximity, but had to make physical contact, ordinarily via the antennae. The antennae of the female, as well as other body regions, contain a chloroform-soluble, nonvolatile substance that will stimulate the male sexually. Thus, sex discrimination by males is mainly owing to "contact chemoreception." It follows that the male German cockroach probably cannot be attracted from a distance by means of synthetic sex attractants (provided they are available) as some other insect species can be.
When male and female meet, their antennae touch and vibrate against each other. The male then turns around, raises his wings to expose the orifices of a pair of dorsal glands located on the seventh and eighth tergites, and extends his abdominal segments to expose the openings of the 2 pairs of glands. The glands are not normally visible, being covered by the wings and by the margins of the preceding abdominal sclerites. Both wing-raising and extension of the abdomen are required to uncover the glands. The female eats a secretion from these glands. After she has fed for a few seconds, the male-pushes his abdomen farther back, and connection of the genitalia is made. The male then moves out from under the female, and the pair remain attached in a linear position for an average of about 86 minutes (Roth and Willis, 1952). These authors also pointed out that the fact that German cockroaches do not need to be attracted from great distances, as do many other insects for the meeting of sexes, is understandable in view of the habits of cockroaches in general. The chance meeting of opposite sexes is enhanced by the fact that they are negatively phototactic and positively thigmotactic (principally guided by contact), and that they are gregarious, with large numbers seeking the same environment. They seek secluded and particularly very narrow hiding places, such as cracks, crevices, and voids, especially those having optimum temperature and moisture conditions. Attraction to the odor of the species is another factor that favors aggregation. Once the sexes have been brought together by these different stimuli, more refined stimuli lead to sexual discrimination.
Life Cycle. The German cockroach lays more eggs and has more generations per year than the other common domiciliary species, and therefore tends to increase in numbers much more rapidly. There may be 3 or 4 generations per year. In one investigation at a temperature of 76° F (24.4° C), the developmental period varied from 54 to 215 days, with an average of 103 (Gould and Deay, 1940). It has been found to be as little as 60 days for males and 65 days for females at 95° F (35° C) and 90 to 95% relative humidity (Ross, 1929). An individual German cockroach, however, lives an average of 200 days at room temperature (Gould and Deay, 1940), and may live as long as 10 months (Truman, 1961a). A comparison of the developmental periods of the 4 principal domiciliary cockroaches at 82° F (28° C) and at ordinary room temperature is shown in figure 149.
The Oötheca (Egg Capsule). The German cockroach female produces her first oötheca 11 or 12 days after becoming an adult (Ross, 1929). 0öthecae can be produced parthenogenetically (without fertilization), but although embryos develop, the eggs do not hatch (Roth and Willis, 1956). Unlike other domiciliary species, the German cockroach female carries her oötheca for as long as a month, until a day or two before the eggs are ready to hatch, then drops it anywhere. The eggs occasionally hatch while the oötheca is still attached. The female generally deposits 4 or 5 oöthecae, but there can be as many as 8. The females of other cockroach species drop the oötheca as soon as it is fully formed. Thus, the abundance of females with their attached, brownish, purseshaped oöthecae (figure 148) is a characteristic of a German cockroach infestation.
The oötheca is about 8 x 3 mm-rather large in relation to the size of the female. As with all common cockroach species, the eggs are located in 2 parallel rows. The locations of the eggs are indicated by corresponding divisions on the outer wall of the brownish oötheca. When the embryos have developed to the point where they exert enough pressure, the oötheca splits open at the top and the nymphs wriggle out. The female will eat the young nymphs if no water is available to her (Ross, 1929).
There are usually 30 to 40 eggs per oötheca, but there can be as many as 48. In one investigation, an average of 29.9 nymphs were hatched per oötheca in an average of about 28 days at ordinary room temperature (Gould and Deay, 1940), while in another investigation at 95° F (35° C), eggs hatched in 14 days (Ross, 1929). After the fourth oötheca is produced, the number of eggs per oötheca gradually decreases to about 75%of the original number in the seventh and eighth oöthecae (Willis et al., 1958).
The eggs become desiccated if the oötheca is removed from the female any time before its normal time to drop, for they must obtain moisture from the body of the mother. The end of the oötheca that is attached to the female is relatively soft and permeable to water, and is not so heavily sclerotized as the posterior end. Roth and Willis (1955) found that German cockroach oöthecae placed with their anterior ends on wet filter paper gained weight, whereas those with their posterior ends on the same wet paper lost weight, even though the humidity was high in the covered petri dish in which the oöthecae were kept. Probably, the wall of the oötheca in contact with the female's genital pouch is permeable to water (Ross, 1929; Parker and Campbell, 1940).
Even before the oötheca begins to emerge, the abdomen of the female is greatly distended. Once the translucent tip of the oötheca becomes visible, the entire oötheca will be fully developed and entirely visible by the following day, changing from white to pink within a few hours. Within a day or two, it becomes light brown and finally chestnut. It is turned with the keel to the left or right (Haber, 1919; Gould and Deay, 1937, 1940).
Nymphal Instars. Wright (1968) found that among 749 German cockroach nymphs, 5.7% emerged while the oöthecae were still attached to the body of the female, 92.9% emerged within 24 hours after the oöthecae were dropped, and only 1.4% emerged thereafter. Among field-collected German cockroaches, 27.9 nymphs per oötheca emerged from those dropped by females collected in summer, compared with only 9.7 from those collected in winter.
German cockroach nymphs have 6 or 7 instars. As in the case of all insects with gradual or incomplete metamorphosis, there is no abrupt change in appearance between immature and adult forms, except that the adults have wings. Nevertheless, the layman will not necessarily associate the tiny, newly hatched German cockroaches or even the more mature nymphs with the adult insects unless he sees all instars and stages together in considerable numbers. The smaller nymphal instars are sometimes isolated from the remainder of the colony, particularly when they have gained access to a crack or crevice too narrow for the older nymphs and adults.
The first-instar nymph is only 3 mm long. The body is dark gray to almost black, except for the second and third thoracic segments, which are pale brown. The pale-brown band conspicuously characterizes the first-instar nymph. In succeeding nymphal instars, the light band becomes narrower and extends in both directions to become a median longitudinal stripe (plate III, 7). In its anterior extension, it eventually becomes the median pale-brown stripe dividing the "two parallel dark streaks" (already mentioned) that characterize the pronotum of the adult. The remainder of this stripe is covered by the wings.
Completely white nymphs or adults may be seen in a cockroach colony. These are newly molted individuals that have not yet had time to harden their cuticles and to acquire the normal color for the species.
A high degree of mortality occurs during the molting periods. Ross (1929) found mortality to be about 50% during each molt except for the last, when it was 40%. He found that about half the insects died of natural causes before reaching maturity. Molted skins were quickly eaten by the nymphs that emerged from them or by other cockroaches that happened to be near-by. On the other hand, Willis et al. (1958) found in their cultures that 85% of the hatched insects reached maturity.
Effect of Excessive Crowding. The author investigated the effect of crowding in a "choice box," 30 cm square and 10 cm high, with a 12-mm hole at the top of the partition wall between the 2 halves (Ebeling et al., 1966). When there are only 20 to 40 cockroaches in the choice box, most of them will spend nearly all their time in the dark half, for they are negatively phototropic. The insects tend to congregate at the intersection of 2 plane surfaces or in corners. When such areas are filled, the insects will gather in small, scattered groups on plane surfaces. However, despite the aggregation pheromone, German cockroaches have some aversion to being crowded too closely together. They prefer to leave some space between themselves and their neighbors. They sometimes initially display aggressive behavior toward their neighbors when actual physical contact is made. However, if large numbers are forced to occupy limited space, they soon appear to get used to this situation.
When 200 adult male German cockroaches were placed in a choice box, only 11% were in the light half 3 days later, compared with an average of 16.2% in the light halves of 5 choice boxes, each containing 20 adult male cockroaches. On the other hand,, when 959 adult German cockroaches of mixed sexes and 530 nymphs were placed in the dark half of a choice box, they were so crowded that they made physical contact with one another, and in some cases were one on top of the other. They were left that way for 2 hours, and then a cork occluding the 12-mm hole in the partition wall was removed. Large numbers of cockroaches left the dark compartment. On the third day of the experiment, the insects were anesthetized and,counted. Of the live insects, 36.1% of the adults and 41.7% of the nymphs were in the light compartment of the choice box, preferring the light to an excessively crowded condition in the dark. If German cockroaches are found in parts of an untreated building far removed from food and water or from preferred habitats, it is an indication of excessive crowding in their customary harborages.
Crowding in Narrow Spaces. Adult German cockroaches can move about in space only 1.6 mm in width or depth (Wille, 1920). When given a choice among 8 spaces between masonite plaques placed one above the other and ranging in distances from 1.6 to 12.7 mm apart, in 1.6-mm increments, 67% of adult German cockroaches gathered in the 4.8-mm space. When the plaques were vertically arranged, this percentage increased to 85. Only a few adults gathered in the 1.6-mm space (Berthold and Wilson, 1967). In our laboratory we found that only the first 3 instars of a population of all ages of German cockroaches crawled from a light to a dark compartment of a 5-cm-wide wooden box for a distance of 2 cm under a strip of masonite that was only 1 mm above the floor of the box. Only 80% of the adult population (6 males and 2 females without oöthecae) crawled through a 2-mm aperture in a 24-hour period, even though the insects were driven by hunger and negative phototropism to seek food and darkness. No adults were able to crawl from the light to the dark compartment when the 2-mm aperture was between the wooden partition wall (1 cm thick) and a masonite ceiling.
The author once observed a severe infestation of German cockroaches in the food-storage room of a large "rest home." Leaking or spilled packages of flour, cereal, or similar foods on the shelves provided plentiful food for the insects. Cockroaches were crowded into a space of 2 or 3 mm between a shelf and the wall. They were completely hidden from view, except for a continuous band of waving antennae that extended from the aperture, and could be seen by looking beneath the shelf.
This.sort of thing is a common occurrence, well known to pest control operators. However, it appears that the first mention of this phenomenon in the literature was in P. B. Cornwell's The Cockroach, and figure 150 is taken from his book.
German cockroaches are also likely to be found in the bathroom, particularly if the kitchen and bathroom share a common wall, for then they can infest a common wall void and pass from one room to the other via areas surrounding utility pipes or the louvers and razor-blade receptacle of the built-in medicine cabinet. In moderate to severe infestations, they can be found throughout the house in protected areas, such as closets, dressers (usually above the top dresser drawer), sofas, electrical appliances such as radios and television sets, under stairwells, behind moldings, picture frames, etc. All such places must be thoroughly treated with insecticide for effective control.
Television sets in particular are becoming increasingly important harborages for both German and brownbanded cockroaches. Not only the warmth, darkness, and the edible glue used in construction, but often the bits of human food commonly found in the vicinity of television sets are attractive to cockroaches and combine to provide an ideal harborage.
In severe infestations, enormous numbers of German cockroaches may sometimes be found in the attic and in wall voids. They use the wall voids to move either laterally or vertically from one room to another or from one apartment to another. They may also be found in the crawl space under the house, at the bases of foundation walls, in cracks in the sidewalk, in the lawn and under shrubbery, and in outdoor incinerators or garbage-disposal bins.
There are other reasons for the increasing dispersal of German cockroaches throughout a house that arise from changes in furnishings and in man's living habits. Central heating has become common, resulting in temperatures in all areas that are conducive to cockroach breeding, even in winter. Even if some rooms are cooler at night, the insects can find warmth in such appliances as electric clocks, radios, or television sets. Some people eat their meals, or at least light snacks, near the television, which could be in the livingroom, bedroom, or den. A few crumbs, pieces of cookies, etc., can sustain many cockroaches. Many modern homes also provide more sources of water than were formerly found in homes. There may be 2 or 3 bathrooms, as well as air-conditioners with evaporating pans. Beer cans and soft-drink bottles not completely emptied may be left in more locations, now that homes are more extensively utilized than they formerly were, and these also provide sources of both food and water.
Among household pests, the silverfish and cockroaches are among the cryptobiotic insects. Although most cockroaches have wings, they use them sparingly or not at all. Accordingly, one might expect that neither silverfish nor cockroaches would be effectively attracted to foods or chemical lures, at least not over distances that might lead to effective chemical trap devices, and this has indeed been found to be true for both these relatively primitive insect orders.
In the case of Blattella germanica and Blatta orientalis, the species aggregation odor was shown to be largely responsible for their gregarious behavior, but the stimulus was effective for only a short distance (Ledoux, 1945). As stated earlier, sex stimulus, although of chemical origin, is limited in cockroaches and requires actual physical contact. Even food odors are only feebly attractive, and will attract German cockroaches only if they occur in areas normally frequented by the insects or in the routes in which they would normally travel. For example, in a room, cockroaches normally travel mainly along wall intersections, the intersections of the floor and the walls, the intersections of the walls and the ceiling, the intersections of shelves and pantry or cabinet walls, and infrequently in other areas.
When experimenting with German cockroaches, Ebeling et al. (1966) found that in a kitchen area in which food was available to the insects, an average of 2.45 per baited trap-jar was trapped in jars placed along the baseboards (intersections of floor and wall), but none in jars placed in the center df the kitchen floor. When all other food was removed from the kitchen, an average of 13.5 insects was trapped in the baited jars placed along the baseboard and 1.15 in the center of the room.
Hunger is one of the factors influencing exploratory activity of cockroaches, but the physical features of a habitat (structural features, temperature, humidity, light) are the principal factors influencing the areas in which the insects will travel.
Factors such as pheromones and food odors can become operative only after these physical features have already attracted the insects. For insecticides or even poison baits to be effective, they must be applied in areas in which cockroaches would normally travel or congregate (Ebeling and Reierson, 1970).
Biology. The field cockroach resembles the German cockroach, and is only slightly smaller. It can be distinguished by the blackish-brown area on the face, from the mouthparts to between the eyes, that is absent from the German cockroach. The 2 parallel, longitudinal stripes on the pronotum of B. vaga are similar to those of B. germanica, but are very dark and more sharply defined. With the aid of a hand lens, the 2 species can be told apart by differences in the subgenital plate (Buxton and Freeman, 1968). The life cycle of B. vaga is similar to that of the German species, but Willis et al. (1958) found an average of only 28 eggs per ootheca, of which 19 hatched, compared with 37 for B. germanica, of which 28 hatched. In B. vaga, after the the third oötheca is produced, the number of eggs per oötheca decreases until in the eighth oötheca it is only 10% of the number found in the first 3. (In the case of the German cockroach, there is a reduction of only about 25%.) Of the hatched insects, 73% reached maturity under laboratory conditions, compared with 85% for the German cockroach.
Habits. The field cockroach is so named because it is ordinarily found outdoors, where it feeds on decaying vegetation, but during the drier seasons, it may invade houses in large numbers. Its feeding habits are similar to those of the German cockroach. Of the 2 species, B. vaga is more likely to be seen during the day, for it is not repelled by light, and in fact is commonly found in the evening around street lights and in display windows. Infestations have been eliminated by removing decomposing plant material from around the foundations of houses (Flock, 1941).
In Texas, a peat control operator who believed he was treating a house for German cockroaches failed to control the infestation. When the insects were found to be field cockroaches, he sprayed the yard, which was the source of infestation, and obtained control (Walter, 1968).
Description. The adult brownbanded cockroach (plate III, 2) is approximately the same size. as the German cockroach. The male is 13 to 14.5 mm long, and the female slightly shorter (11 to 12 mm). The abdomen of the female is much broader and more rounded posteriorly than that of the male. The wings of the male cover the abdomen completely, while the wings of the female are short, and never cover the entire abdomen. Males may often be seen flying when a colony is disturbed, but the females cannot fly.
From the dorsal aspect, the adults are dark brown, particularly the head and thorax and the exposed segments of the female, which may in fact range to black. The wings of the female are reddish brown to very dark brown throughout, while those of the male are dark brown at the base, becoming increasingly lighter posteriorly. Both sexes have a band of pale brown at the base of the wings and another band of pale brown a third of the distance from the base, which gives the adults a "banded" appearance. The wings and body of the female are much darker than those of the male. The ventral body surface and legs of the male and the legs of the female are light strawcolored. The lateral margins of the pronotum of both sexes are translucent, and this is also true of a narrower lateral margin of the anterior portion of the wing. The ratio of females to males was found in one investigation to be 1.32:1 (Willis et al., 1958).
Life Cycle. The developmental period of the brownbanded cockroach is considerably longer than that of the German cockroach, as shown in figure 149. The temperature for optimum development is above 80° F (27° C) (Gould and Deay 1940), and homes are seldom kept at such high temperatures. Therefore, the biotic potential for the brownbanded cockroach is considerably less than for the German cockroach. In California, it is found in only about 51% as many homes as the Geiman cockroach, but where food is abundant and temperatures are high, the species can become extremely plentiful.
The Oötheca. The females carry their capsules for 24 to 36 hours before attaching them to some object, possibly the kitchen sink, furniture, walls, shelves, bedding, draperies, behind pictures on walls, or other handy places, usually in clusters corners under chairs and tables are among the favored places. Individual clusters (figure 151) on the walls of rearing cans in the author's laboratory have at times contained 50 or more egg capsules. One housewife, in attempting to describe them, said they appeared to be "clusters of seeds". This habit of attaching the oöthecae to furniture and other household objects results in the species being readily disseminated over great distances. The oötheca of the brownbanded cockroach measures about 4 x 2.5 mm-the smallest of the common domiciliary cockroach oöthecae. It varies in color from yellowish to reddish brown. A few days after it is formed, the fertile eggs show greenish through the walls of the oötheca, and shortly before hatching, the eyes of the young are visible.
The incubation period for the eggs of the brownbanded cockroach was found to be the longest among 6 cockroach species investigated by Gould and Deay (1940). It averaged 49 days at 82° F (28° C) and 95.6 days at 72.5° F (22.5° C). About 14 fertile oöthecae were formed per female. The maximum number of eggs normally produced per capsule was 18, but the average number hatching was 13.2.
Nymphal Instars. From the dorsal aspect, the nymphs (plate III, 7) are also basically dark brown in color, but with a narrow, pale margin on the thorax. The meso- and metathorax are pale brown, and the abdomen has a broad, pale area. The dark and pale areas of the nymphs are in striking contrast, and easily identify this species. (The nymphs could more appropriately be called "brownbanded" cockroaches than the adults.) There are 6 to 8 nymphal instars. At room temperature, Gould and Deay (1940) found the average period for nymphal development to be 161 days for males and 162 days for females, but at about 85° F (29° C), the average periods were 90 and 95 days, respectively. At room temperature, extremes of developmental periods were 95 and 276 days. The length of adult life varied from 131 to 315 days, with an average of 206 days.
Habits. The brownbanded cockroach was once believed to be unique among domiciliary cockroaches in its tendency to distribute itself throughout a house, even in bedrooms, furniture, and closets, particularly on high shelves, behind pictures on walls, and behind moldings. Gould and Deay (1937) stated, regarding this species: "Except when in search of food, it seldom visits the kitchen, and confines its activities to other parts of the house." About the German cockroach, they stated: "In an infested home, it is confined to the kitchen and lavatories, where it hides behind baseboards, in cupboards, iceboxes, and dark corners, and around water pipes." Apparently, the habits of the 2 species have changed, for now there appears to be no great difference in the way they are distributed in a house or apartment. As already stated, Shuyler (1956) believed the change in the habits of the German cockroach coincided with widespread resistance to chlordane, which in the years following World War II was almost universally used for control of this species. Both species are now most abundant in the kitchen areas, and either can be widely distributed throughout a house or apartment. Sometimes, mixed populations of the 2 species are seen. However, as stated earlier, infestations of brownbanded cockroaches generally occur only in houses or apartments in which temperatures are higher than most people would consider to be comfortable.
In California, the oriental cockroach is found in homes more frequently than the brownbanded cockroach, but does not reach such large numbers or become so widely distributed in the house. Nevertheless, pest control operators report more calls for control of the oriental than of the brownbanded cockroach. Its large size and black color cause it to be regarded as a particularly repulsive pest. The housewife prefers to believe that the insect is a "water bug" or "black beetle" rather than a cockroach, but usually loses no time in calling for the exterminator.
Description. The adult females of the oriental cockroach are about 3 cm long. The male is about 2.5 cm long, and is much narrower than the female. Both sexes vary from dark reddish brown to black, usually the latter (plate III, 3). The female has small, rudimentary, functionless wings, and the male, although it has well-developed wings covering about 75% of its abdomen, does not fly. The tarsi of both nymphs and adults lack an arolium (cushionlike pad between the claws), and there they cannot climb smooth, vertical surfaces. This species is relatively sluggish in its movements. The ratio of females to males has been found to be 1: 1.15 (Willis et al., 1958).
Life Cycle. As shown in figure 149, the developmental period of the oriental cockroach is more than a year, even under indoor conditions, and for some individuals it may be prolonged to about 2 years. The insect may also live for long periods after reaching maturity. Gould and Deay (1940) found that at room temperature, the length of adult lives of 5 females varied from 34 to. 181 days. Among 4 males, the length of adult lives varied from 112 to 160 days. Whereas it may require a long time for an appreciable infestation of oriental cockroaches to develop, enormous populations are eventually possible. Ordinarily, the oriental cockroach does not become so abundant as the German cockroach in buildings, but can become very numerous in secluded places, such as basements or crawl spaces, if they are damp. The species thrives better outdoors than other domiciliary cockroaches in the United States, even under quite severe climatic conditions.
The 0ötheca. The female carries her oötheca for about 30 hours after it is formed and filled with eggs. It is dropped, or attached to debris or food material, in some protected place. It is large (10 x 5 mm), and when first deposited it is reddish brown and soft, but becomes black, hard, and brittle. Although the number of oöthecae.formed varies greatly, in an observation of 8 females, the average number was 8. A perfect capsule contained 16 eggs (Gould and Deay, 1940). Another investigator observed that females produced from to 4 oöthecae, with the usual number being 2 (Rau, 1924). The incubation period was noted to vary from 42 days at 29.5 °Cto 81 days at 21 °C (85 and 70 °F), and was approximately 2 months at the usual room temperatures.
Nymphal Instars. The newly hatched nymph (plate III, 7) is only about 6 mm long, and pale brown. It becomes more reddish with succeeding instars, and finally, in the last instars, dark reddish brown to black, like the adults. At ordinary room temperatures, the period for nymphal development averaged 515 days for males and 542 days for females, whereas at 82 °F (28 °C) it averaged 288 days for males and 310 for females. Willis et al. (1958) found the period for nymphal development at 30° C (86 °F) to be 164 days for males that had the maximum of 7 instars, and 282 days for females that had the maximum of 10 instars. The oriental cockroach seems to have a seasonal cycle, with the adults appearing in May and June and dying during July (Gould and Deay, 1940; Rau, 1924).
Habits. In the southern areas of the United States, this species has long been known as the one best able to survive outdoors. Its temperature preferences are somewhat lower than those of the German cockroach, and it can thrive in both drier and cooler areas (Gunn, 1935). Like some other cockroach species, Blatta orientalis appears to be changing its habits. It can now survive outdoors farther north than it could originally. Shuyler (1956) observed that oriental cockroaches survived outdoors during 13 weeks of almost continuous freezing weather with a light snow cover. They could be found by moving stones, leaf debris, and clods of soil near a house. About 2 weeks after the arrival of the first warm weather of spring, these insects invaded the house.
Although once known to occur mainly under a house, in the crawl space, basement, or cellar, or on the first floor, particularly around sources of water, the oriental cockroach is now reported with increasing frequency inside at higher levels - as far up as the fifth floor (Shuyler, 1956). In southern California, it is often abundant in the dense vegetation of estates in areas in which some of the cleanest and most elegant homes are located. Its entry into such homes may be purely random movement, generally under sliding glass doors or around utility pipes, air ducts, and ventilators leading from a damp crawl space.
In some localities, oriental cockroaches can be collected at any time of the year from the dark, damp, water-meter vaults that are typically located in the ground in alleys and parkways.
Anything done to increase light, improve air circulation, and decrease dampness in dark, damp basements and crawl spaces will reduce the oriental cockroach infestations, for they can otherwise become established in enormous numbers in such areas.
The "Cockroach Odor." The oriental cockroach possesses in abundance the much-despised "roachy" odor that is associated with cockroaches. Those who believe that everything in nature must serve some useful purpose for mankind will be encouraged by the following account of the alleged usefulness of the "essence" of oriental cockroaches, taken from the 1907 edition of the highly respected Merck's Index:
Constituents: Blattaric acid; antihydropin; fetid, fatty oil. Uses: Internal, in dropsy, Bright's disease, whooping cough, etc. External, as an oily decoction for warts, ulcers, boils, etc. Doses: 10-15 grains in dropsy, as powder or pills, or 4 fluid drams' decoction. (Illingworth, 1915.)
Description. The adult American cockroach (plate III, 4) is about 4 cm long. The males appear to be considerably longer than the females because their wings extend 4 to 8 mm beyond the tip of the abdomen, while those of the females do not. When 25 males were measured from the tip of the head to the tips of the wings, they were found to average 39.2 mm in length. Measured from the tip of the head to the tip of the abdomen, 25 male American cockroaches averaged 34.3, mm and 25 females averaged 34.4 mm. There was no significant difference in the average width of males (12.2 mm) and females (12.0 mm). (See table 41 under "Brown Cockroach.") The American cockroach is reddish brown throughout, except for a pale-brown or yellow band around the edge of the pronotum. The band is widest at the posterior margin. Both sexes have a pair of slender, jointed cerci at the tip of the abdomen. The cerci of the females have 13 or 14 segments and those of the males have 18 or 19 (Bugnion, 1922). The males have a pair of styli between the cerci. The presence of 2 pairs of appendages at the tip of the male's abdomen, compared with 1 pair in the female, is one of the morphological features separating the sexes. Among laboratory-reared American cockroaches, there have been recorded ratios of females to males of 1:1.07 (Gould and Deay, 1940) and 1.08:1 (Willis et al., 1958). It therefore appears that the sexes may be about equal in numbers.
Life Cycle. The developmental period of the American cockroach is greatly dependent on temperature (figure 149), but it averages about 600 days under ordinary room conditions. After reaching sexual maturity, the average life of the females may be another 400 days (Gould and Deay, 1940).
The preferred temperature for adults and nymphs was 28 °C (82.4 °F), but they remained active at 21 °C (70 °F). At 29 °C (84 °F), the life expectancy averaged over 630 days, but was found to be as long as 1,293 days. The adult life span at 29 °C ranged from 90 to 706 days (average 225 days) for females and from 90 to 362 days (average 200 days) for males (Griffiths and Tauber, 1942).
Under suitable conditions, the longevity and high reproductive potential of the American cockroach may result in enormous populations. This is evident to anyone who has reared the species over a period of years. It is also evident from the great numbers that can be found in sewer systems. As many as 5,000 American cockroaches have been vacuumed from a single manhole in the Los Angeles city sewer system (Wagner et al., 1966).
The Oötheca. The oötheca (plate III, 4) measures 8 x 5 mm, is brown when deposited, and turns black in a day or two. The lateral indentations marking the locations of the eggs are only weakly indicated. Along the upper ridge of the purselike egg case there is a series of "teeth," marking the location of corresponding eggs, and each tooth has a minute opening at its apex.
The female deposits each oötheca near a source of food, usually within a day after it is formed, either dropping it or gluing it to a suitable surface with a secretion from her mouth. If the female has the opportunity to do so, she hides the oötheca with great care in a crevice, or buries it in soft wood or available debris. The oöthecae of the American cockroach require a high relative humidity for successful hatching (Tsuji and Mizuno, 1971). That may be the reason that in semiarid regions such as southern California, this species is found in large numbers only in damp locations, such as sewer systems, damp basements, the dishwashing rooms in restaurants, and warehouses with inadequate ventilation. Often during the latter part of their lives, American cockroaches deposit their eggs unprotected by an egg case (Gould and Deay, 1940), thus anticipating the egg-laying habit of the descendants of cockroaches, the termites (Rau, 1941). From 15 to 90 oöthecae (average 57.6) were produced at the rate of about 1 per week, and each contained 14 to 16 eggs. This constituted an enormous production of oöthecae when compared with most other cockroach species. The average hatch from 534 oöthecae at room temperature was 13.6 nymphs (Gould and Deay, 1940).
In another similar investigation, an average of only 21 oöthecae per female was observed (Griffiths and Tauber, 1942). Nigam (1933) observed that oöthecae were generally produced in summer, beginning in April and May, but very few during winter. At a temperature of 24.4 °C (76 °F) the average incubation period was 57.4 days, but at 30 °C (86 °F) it was 31.8 days.
Nymphal Instars. According to Gould and Deay (1940), it was difficult to determine the number of nymphal instars. Molting required only a few minutes, and the cast skin was usually eaten. From an examination of a large series of nymphs, they concluded that there were probably 13 instars.
The first-instar cockroach, immediately after hatching, consumes its castoff embryonic skin. It is white, then becomes grayish brown. It attains a length of 3.5 mm. In the early instars, the females have a median notch on the posterior margin of the ninth sternite, whereas in the males, this margin is either smooth or only slightly indented (Gould and Deay, 1940).
After the first instar, the succeeding instars are almost uniformly reddish brown, although the posterior margins of both thoracic and abdominal segments are of a darker color, giving the insects a transversely striped appearance (plate III, 8; figure 152). Wing pads are first noticeable in the third or fourth instar. These gradually become larger, and in the last nymphal instar they are about 7 mm long, distinct, and show venation. Prominent cerci and much smaller styli are present on nymphs of both sexes. In the next to the last instar, they may be hidden by the seventh sternite in females. As already stated, the styli are not present in adult females, and the presence or absence of styli is a convenient criterion for distinguishing males from females. In the final molt, the completely formed wings appear, requiring 25 to 30 minutes to expand completely. The cast skin is not eaten, although it has usually been eaten in all the preceding molts. Complete coloration requires 4 or 5 hours (Gould and Deay, 1940).
Habits. In southern California, the American cockroach is almost the only species found in the manholes and laterals of the sewer system, but it is seldom seen elsewhere - rarely in houses and apartments. Mallis (1969) estimated that in 177 apartments in 3 Texas cities, 99.7% of the cockroaches were Blattella germanica, 0.2% were - Periplaneta spp., and 0.1%, were Supella longipalpa. No Blatta orientalis were found in apartments. In North Carolina, 4 pest control servicemen made a survey in 3 cities to determine the percentage of apartments infested with the 4 principal domiciliary cockroach species among the infested buildings in housing projects in their regular monthly routes. They found B. germanica in 90% of the infested buildings, S. longipalpa in 9%, and P. americana in 1 % (Wright, 1965a). As in the Texas survey, no B. orientalis were found in multiple unit apartment buildings. However, when all types of buildings were surveyed, B. germanica accounted for 54% of the infestations and B. orientalis was second with 34%. Infestations of Periplaneta americana were found in 8% and of Supella longipalpa in 4% of the infested structures (Wright, 1965b). On a military base in North Carolina, percentages of the 4 species were: German, 84.9; American, 14.4; brownbanded, 0.5; and oriental, 0.2 (Wright and McDaniel, 1969).
The author has not been able to provoke American cockroaches to fly, merely by shaking them out of a maze. However, on a sunny day in July, at a temperature of 70 °F (21 °C) and relative humidity of 62%, some male and female American cockroaches were taken from rearing cans and thrown into the air to observe flight performance.' Some fluttered downward to ground positions, but others flew gradually upward, some so far that they were lost from sight. Along the Gulf Coast of Texas, American cockroaches have been observed to be common in palm trees and flying around street lights (Gould and Deay, 1940). In Needles, California, an extremely hot desert area, they are commonly seen flying outdoors, both day and night.
Mass Migrations. In common with Blattella germanica, Periplaneta americana sometimes engages in mass migrations. The former migrates by crawling (Howard, 1895; Marlatt, 1908; Guldin, 1967), but the American cockroach can migrate either by crawling or flying. Gould and Deay (1940) observed that during the summer, American cockroaches had migrated from store buildings for a distance of 4 blocks to some decaying maple trees in which they were infesting cavities. Another instance has been reported of these insects being found near an infested hospital, under the loose bark of large shade trees where they were feeding on exuding sap (Anonymous, 1967e). Migrations from restaurants and city dumps have also been observed (Gould and Deay, 1940). Both American and oriental cockroaches are known to be able to enter houses and apartments from sewers via the plumbing; control of cockroaches in sewers has decreased the infestations in near-by homes (Roth and Willis, 1957).
In experiments on the control of cockroaches with 10% DDT dust in houses, Stenburg (1947) found that the treatment was more effective against American than German cockroaches. He attributed this to the fact that American cockroaches traveled greater distances and thereby increased their chances of encountering the dust. He observed that German cockroaches appeared to move only short distances from their resting places, and apparently always returned to these harborages after searching for food and water.
Description. Measurements were made of widths (distance across wings at widest point when at rest) and lengths (distance between tip of head to tip of abdomen) for 25 males and 25 females of Australian and American cockroaches. These figures are shown in table 4, on the next page. Although there is but little difference between the 2 species in width, the male Australian cockroach is only 83% as long as the male American cockroach, and the female Australian species is 92% as long as her American counterpart. The basic reddish-brown color, and even the pattern of yellowish markings on the pronotum, are similar to those of the American cockroach. The markings (in the pronotum are more distinct, and in addition there is characteristically a lightyellow streak on the outer edge at the base of each forewing (plate III, 5). The ratio of females to males is about 1:1.
The early nymphal instars have a variable color pattern of predominantly brown, but with a narrow margin of black, as well as some light-yellow spots on the abdominal tergites. Later instars are basically reddish brown, but strikingly marked with light-yellow marginal spots on both thoracic and abdominal tergites (plate III, 8).
Life Cycle. In experiments made at 30° C (86° F), Willis et al. (1958) found the preoviposition period of the Australian cockroach to be 24 days. Between 20 and 30 oöthecae were produced. The interval between successive oöthecae was 9.8 days, the incubation period was 40.3 days, the number of eggs per oötheca was 23.8, and the number hatched per oötheca was 16.4, stated as averages. The percentage of hatched insects that matured was 55, compared with 84% for the American cockroach. Among nymphs reared alone, females had 11 or 12 instars, and the periods for nymphal development were 253 and 410 days, respectively. Males had 10 or 11 instars, and the developmental periods were 306 and 365 days, respectively. For females reared in groups, the period for nymphal development was 213 days, and for males-it was 198 days. Thus, nymphs reared in groups matured more rapidly than those reared alone.
Habits. In infested premises, P. australasiae occupies habitats similar to those occupied by P. americana (Cornwell, 1968). It is a pest of buildings in many areas of the tropics, but as just stated, in southern California the author has found it abundantly only in orchid glasshouses. The most common habitat in the glasshouses was in the space between small pots placed within the size larger pot to provide stability to small plants during watering. There is about 2 cm of space between the bottoms of the 2 pots, and this space is very damp. Australian cockroaches were found principally in these spaces, in large numbers.
The Australian cockroaches were feeding on orchid flowers and tender growth terminals. Although German cockroaches were feeding on these as well, the Australian cockroach is particularly known for its propensity for feeding on tender greenhouse plants. It has been reported to cause damage to plants in the tropical house of the Royal Botanic Gardens at Kew, England (Cornwell, 1968). In Denmark, P. australasiae occurred in large numbers in an indoor garden room of a Copenhagen restaurant, primarily in the plant beds, but sometimes it was seen by guests at tables. It had not yet spread to the kitchen or other parts of the restaurant, where the German cockroach was abundant. It was believed to have been introduced with plants from a greenhouse in the Netherlands (Anonymous, 11967e).
Despite the close resemblance of P. brunnea and P. americana, hybridization does not occur. A mixed colony of these 2 species plus P. fuliginosa was maintained for more than 3 years without the production of any recognizable hybrids (Eddleman and Simon, 1969).
Description of Adults. The adults are dark reddish brown (plate III, 6), resembling the American cockroach, but are somewhat darker in color. The 2 species also resemble each other in the yellowish margin of the pronotum. When measuring 25 individuals of each sex among those reared in our laboratory, the lengths and widths of Periplaneta americana, P. brunnea, and P. australasiae were recorded, and are shown in table 4. The data show that the American and brown cockroach are similar in length, but that the latter is the wider of the 2 species. The wings of the male brown cockroach do not extend beyond the tip of the abdomen as far as those of the American cockroach. Both the brown and the American cockroaches can be distinguished from the Australian cockroach by their slightly larger size and the absence of the yellowish streak on the outer edge of the base of each forewing that so distinctly characterizes P. australasiae.
The cercus of the American cockroach is stout basally, and tapers markedly toward the tip (Pratt, 1955). The sides of the last segment are more or less parallel, and 2 or more times as long as the basal width. The cercus of the brown cockroach is also stout, but the appendage is more evenly spindleshaped, with the last segment somewhat triangular and less than twice as long as its basal width. Periplaneta brunnea can fly, but its flight is usually of the gliding type.
Life Cycle. Judging only from the enormous production of P. brunnea in our rearing room at normal room temperature when compared with other species of Periplaneta, it appears to have an alarming reproductive potential. Possibly. there are ecological factors under actual field conditions that have thus far resulted in this species being generally less abundant than the American cockroach, even in the South.
Copulation occurred within a few hours after a female completed development, and egg deposition began 16 to 20 days later. It continued throughout her life. The periods between oötheca depositions varied greatly, but could be as little as 5 to 6 days. Pope (1953) found that the maximum number of ovipositions was 30, but usually it was less. Edmunds (1957) kept some P. brunnea for 20 months, and they were still living and reproducing.
The Oötheca. While the oöthecae of the American and Australian cockroaches are similar in appearance, those of the brown cockroach are strikingly different. Reierson and Ebeling (1970) found that the oöthecae from a colony of brown cockroaches reared on Purina Dog Chow at 80 °F (27 °C) were 13.5 mm long (range 12 to 16 mm) and 5 mm wide at the widest point (range 4.5 to 5.5 mm). Those produced by Australian cockroaches reared under the same conditions averaged 10.9 mm long (range 10 to 11.5 mm), except for 1 oötheca that was 13 mm long. Their average width was 4.4 mm (range 4 to 5 mm). The oöthecae of American cockroaches averaged 8.3 mm in length (range 7.5 to 9.5 mm), and were about as wide as those of the brown cockroach. Thus, the oöthecae of the brown cockroach averaged 2.6 mm longer than those of the Australian species, and 5.2 mm longer than those of the American cockroach.
Edmunds (1957), conducting all his experiments at 75 °F (24 °C), found that P. brunnea deposited the oötheca from 20 to 24 hours after it was extruded. The number of eggs per oötheca averaged 24 (range 21 to 28). Reierson and Ebeling (1970) obtained an average of 23.8 eggs per oötheca at 80 °F (27 °C) and 65 to 75% relative humidity. The incubation period at this temperature was 35 days, compared with 61 to 63 days at 75 °in the Edmunds experiments.
The oöthecae are at first brownish, but become black with increasing age, a characteristic of cockroach capsules. In large plastic rearing cans, the brown cockroach glues many of its eggs to the vertical interior walls of the cans or to the corrugated-paper mazes (Ebeling et al., 1966). In glass jars, the female frequently glues her oöthecae to the jar lids. Under similar rearing conditions, the American cockroach glues her oöthecae to the floor of the container. Both species at least partially cover their oöthecae with bits of paper, cotton, or other available debris in an apparent instinct to hide them.
An interesting aspect of the biology of P. brunnea was brought to light by Willis et al. (1958), who found that eggs hatched from 91% of parthenogenetically produced oöthecae and that 31.7% of the 208 hatched nymphs matured. All were females.
Maternal Care for Eggs. Cockroaches share with the somewhat related termites and earwigs the instinct of maternal care for their eggs. Edmunds (1957) described the phenomenon with respect to P. brunnea as follows:
In ovipositing, the female roach secreted from her mouthparts a frothy white substance which she seared over the spot in which she was going to deposit the egg capsule. Some females spent from 30 to 40 minutes preparing this frothy bed. The egg capsule was then deposited in the froth and covered with additional froth secreted by the female. Some cockroaches were observed spending, as much as 2 hours coating the egg capsule after it was deposited. The substance hardened to become a very strong cementing material. It was so strong that it was difficult to pry the capsule loose without causing it to rupture. For several hours after a capsule was deposited, the female rested with her body over the capsule and drove away any other roaches which approached.It may be that if the oöthecae of the brown cockroach were not guarded by the female, they would be in danger of being consumed by other cockroaches during the period when she customarily remains with them, since many are later found and eaten. Cockroaches that are injured or weakened in some way are also eaten by others. This may also be observed among other cockroach species.
Nymphal Instars. In the first-instar nymph, whereas the antennal segments of the American cockroach are uniformly brown, the first 8 and last 4 segments of the brown cockroach are white, and the intermediate ones are brown. The first instar nymph of the Australian cockroach resembles the brown cockroach in this respect. A median translucent area in the mesothorax of the brown cockroach nymph is absent in Perplaneta americana. The first 2 segments of the abdomen of the first-instar nymph of the American cockroach are entirely gray, brown, or reddish, while those of the brown cockroach have faint, cream colored spots on the dorsolateral margins. In later instars, these dorsolateral spots are extended to and include the sixth segment of the abdomen. The intermediate nymphal instars (plate III, 8) of the Australian cockroach are similar to those of the brown cockroach, except that the cream colored markings are more distinct, and extend throughout the length of the abdomen (Edmunds, 1957; Reierson and Ebeling, 1970).
Edmunds also observed that at 75 °F (24 °C), out of 25 newly emerged nymphs, the first male completed development in 263 days and the first female in 268 days, but that all nymphs had completed development in 277 days. The entire life cycle of the brown cockroach, from egg to egg, varied from 339 to 351 days - relatively brief when compared with the American cockroach.
Parcoblatta pennsylvanica happens to have the widest distribution, but there are at least a dozen other species of the genus that occasionally find their way into houses in the United States, particularly P. lata (Brunner) and P. virginica (Brunner). Species of Parcoblatta are found throughout the country. They are generally seen in wooded areas, but one, P. desertae (Rehn and Hebard), is found only in desert and semidesert mountains of the Southwest (Rehn and Hebard, 1909; Hebard, 1917, 1942). Parcoblatta americana (Scudder) is the only species of the genus found in California. It is small, the males being 12 to 14 mm long and the females 9 to 13 mm. The females are wingless. The color is generally shining buff or brown, ranging to black in some females in the region of Mount Shasta, California. The smaller and paler specimens are found in the more arid and barren regions (Hebard, 1917).
Where the climate is favorable, the Surinam cockroach is generally found outdoors under rocks and boards, under litter, or in damp soils. In Hawaii, it has been found in soil around the roots of pineapple, under mulching paper, or even feeding on pineapple roots (Illingworth, 1927, 1929). In colder regions, this species can sometimes be found in greenhouses, where it can cause damage to plants. In some Philadelphia greenhouses, Surinam cockroaches were present "by the millions." From 30 to 50 thousand rose plants out of 200 thousand were so severely injured by the gnawing off of the bark, young buds, and shoots of the main stems that they had to be discarded (Doucette and Smith, 1926). In a greenhouse in Germany, many of these cockroaches penetrated soil to a depth of 8 to 10 cm, and a few even more deeply. Some insects spent several days at a time in chambers at the bottoms of the holes. Nymphs molted and females produced their young in such chambers (Roeser, 1940). Pycnoscelus surinamensis is parthenogenetic in North America and Europe, and the offspring are all females, but it is bisexual in Indo-Malaysia (Roth and Willis, 1956).
The Madeira cockroach is frequently intercepted in quarantine at seaports, which is understandable in view of its predilection for fruit, particularly bananas (Sein, 1923). Despite the high temperature requirements of this species, it can adapt itself to sheltered life in temperate climates, as shown by its establishment in New York City in buildings having sufficiently high temperatures. There appears to be no reason why it could not become more widely distributed. The brownbanded cockroach also requires relatively high temperatures, but has nevertheless become widely distributed throughout the United States (Gurney, 1953).
This cockroach is of great interest because of the presence in its alimentary canal of cellulose digesting, flagellated protozoa, transferred from older insects to the young as in the termites, which are believed to be descended from the cockroaches. The first fecal pellets passed by the older nymphs after a molt contain large numbers of encysted protozoa. When eaten by the newly hatched nymphs, these cysts ensure a heavy population of flagellates within a few days. Cryptocercus depends on these flagellates for the digestion of cellulose.
One genus of flagellates (Barbanympha) contained the largest and most abundant species found by Cleveland et al. (1934) in every one of the thousands of Cryptocercus they examined. They contained the enzymes cellulase and cellobiase, which the cockroach itself was unable to produce, and these enzymes converted cellulose into soluble sugar (dextrose) (Trager, 1932). Cryptocercus possesses 2 genera of protozoan symbionts (Trichonympha and Leptospironympha) that are also present in termites (Honigberg, 1970). Transfaunations can be achieved between Cryptocercus and Zootermopsis by feeding one the intestinal contents of the other (Cleveland et al., 1934; Nutting, 1956).
Water is often available as condensation or spillage under the refrigerator. Patches of water often remain for hours in certain locations after a floor mopping or following the use of a washing machine. Other common sources of water for cockroaches are the traps of sinks, washbasins, tubs' and toilet bowls; flush tanks; condensation on cold pipes and windows; leaking pipes and faucets; miscellaneous water-filled containers such as pets' drinking dishes, aquaria, vases, empty beverage bottles; and the juices from soft fruits and vegetables (Roth and Willis, 1960).
Cockroach infestation is favored by a cluttered household. Stored magazines and newspapers, corrugated-paper boxes and piles of paper bags should be eliminated. They not only provide harborage and breeding areas for cockroaches, but also provide areas into which the cockroaches can escape from insecticide residues when control is attempted. Insecticides are repellent to cockroaches in varying degrees.
Application of Insecticides. If liquid sprays are to be applied, and ideally for dusts also, all shelves and drawers should be emptied and cleaned. After treatment, shelf paper may be placed on sprayed areas and on dust deposits. If a relatively safe dust such as boric acid is to be used, it is recommended that the operator reach carefully behind shelf contents and apply the dust with a bellows powder blower ("Getz Gun"), bulb duster, or plastic squeeze bottle (figure 29, chapter 3) in a narrow band along intersections and into corners and crevices. Shelf paper lifted while the powder is applied may then be allowed to fall back into place.
When applying insecticides for cockroach control, pest control operators ordinarily ask the occupants of the treated premises to remove cooking and eating utensils and foodstuffs when there is danger of their becoming contaminated with insecticide. For example, they may be placed on a table in the center of a room and covered with a sheet. Occupants are asked to leave the building and remove their pets during treatment.
Treatment for cockroaches, like so much of household pest control, is "spot treatment." The insecticide is applied to relatively limited areas where cockroaches are likely to hide during the day or where they are likely to travel at night. Most cockroaches congregate in dark, warm. damp places, such as under and behind the refrigerator and stove and under the sink, particularly the "dead space" between the sink and the wall. The most thorough treatment can be made under the refrigerator and stove if the kick panels are first removed, allowing the person applying the spray or dust to see what he is doing. Many cockroaches seek harborage and breed in the insulation in the walls of a refrigerator, stove, or range. These insects should come in contact with insecticide residues when they come out to forage for food and water. Insecticide sprays should also be applied behind window and door frames, under and behind furniture standing against the wall, on the undersides of tables and chairs, on closet and bookcase shelves, and in cracks and apertures around cabinets. Cockroaches are attracted to warmth, and may hide under and behind radiators and water heaters or in television sets and radios. Apply enough spray to wet surfaces thoroughly, but not enough to drip or run. If both sprays and dust are to be used, spray first and apply the dust after the spray dries, forcing the dust into cracks and voids.
When cockroaches are abundant, they are likely to be located in wall voids. In apartment houses, they may migrate from heavily infested to lightly infested or uninfested apartments via these voids. After blowing an insecticide dust into openings around utility pipes or any other openings into walls, particularly in kitchen and bathroom areas, such openings should be sealed to prevent further ingress or egress of the insects. Holes through which to dust wall voids can be drilled through plaster if necessary, and the holes can then be filled with matching plaster. Holes can also be drilled at the top of the kick panel under a kitchen cabinet, or in the floor of the cabinet, in order to dust the subcabinet voids, unless the latter can be reached by removal of drawers or through existing cracks or apertures. After treatment, seal all cracks and crevices where cockroaches may hide. Even very narrow cracks may harbor the small nymphs. If the backsplash behind the sink and on the sink cabinet has parted from the wall, leaving a narrow aperture, this is a particularly favored harborage for cockroaches and should be sealed.
Pyrethrin aerosols are commonly used to flush cockroaches from their daytime hiding places for pre- or post-treatment estimates of infestation levels in buildings, or to drive the insects from their hiding places so as to facilitate treatment with residual insecticides. Pyrethrins and their synergists are also added to insecticide solutions or emulsions for more rapid knockdown or presumed increase in the efficacy of the sprays. In field tests in which pyrethrins plus synergists were added to 3 insecticide solutions, 1 emulsion, and to boric acid powder, the pyrethrins resulted in more rapid knockdown, but evaluations made a month after treatment did not reveal, on the average, any increased insecticidal efficacy (Ebeling and Reierson, 1973a). In addition, when pyrethrins were used in apartment buildings they had the disadvantage of driving cockroaches from the treated apartment to adjacent untreated apartments via the wall voids.
Pyrethrin formulations, particularly dusts, frequently cause allergic reactions in people with such allergic tendencies as hay fever and asthma. Some persons applying certain organophosphorus insecticides suffer respiratory disorders, but the carbamate propoxur has not been reported to have this disadvantage (Lisella, 1973).
Resmethrin is a synthetic pyrethroid that has been suggested as being much less irritating to the throat than pyrethrins. Resmethrin does not seem to flush cockroaches out of their hiding places as quickly as pyrethrins, and the insects appear to be less agitated. However, within 15 to 20 minutes, a greater proportion of the cockroach population is said to be flushed out, providing a more accurate estimate of the infestation level (Grothaus et al., 1972).
If base oil (deodorized kerosene) is used as a carrier in the spray, it should not be applied near a flame, as under a gas-operated water heater; a water-base spray (emulsion) should be substituted in areas of fire hazard. Ideally, base-oil solution should not be applied to plaster, asphalt tile, or linoleum, for it leaves an oily stain on plaster, destroys the waxy finish on tile or linoleum, and leaves a slippery surface that may be hazardous to occupants of the sprayed building. Base oil sometimes penetrates between old floor tiles and weakens their bonding to the floor. In cockroach control, it is necessary to spray beneath and behind the refrigerator and stove and along baseboards, and thereby get base oil on the floor at least in these out-of-sight areas. An experienced serviceman sometimes sprays with base-oil solution along baseboards in other areas when the floor is covered with tile or linoleum, but he sprays very lightly. Most disadvantages of base oil can be avoided by using water as the carrier. However, water emulsions have their disadvantages also. They tend to leave visible residue ("spots") when the emulsion dries. Either base oil or water will leave unsightly residues if applied over greasy or dirty surfaces to the point of runoff, for this may cause streaks to form around the treated area.
The residual efficacy of insecticides applied in liquid sprays is greatly affected by the nature of the treated surface, as shown in table 5. Dust deposits are less affected by the substrate, and this is one of the advantages of dust formulations.
Dusts can be applied most effectively in cracks, crevices, and enclosed spaces such as wall voids, voids under cabinets, and voids under built-in appliances. In visible places, such as along baseboards and moldings and in bathrooms, dust deposits are unsightly and liquid sprays are more appropriate. In the bathroom, there are few places where dusts are not unsightly, but if they are blown into the louvers or razor-blade slots of medicine cabinets, they can be widely distributed in a wall void that is likely to harbor cockroaches. The best results are obtained with both spray and dust, each in appropriate locations. A spray or dust treatment, or a combination of the two, can be effectively supplemented with cockroach bait that may be placed in out-of-sight areas similar to those in which a dust would be applied. Dichlorvos bait initially kills cockroaches more rapidly and completely than Baygon or Kepone, but the latter provide longer residual control. Glycerol has been found to be effective as a feeding stimulant in poison baits, and is much more so than maltose, the most effective of the sugars (Tsuji and Ono, 1970b).
The efficacy of resin strips depends on the concentration of dichlorvos vapor they can generate in the area to be treated. In a normally ventilated room, the concentration does not reach a sufficiently high level for cockroach control, but the strips are effective against them in enclosed spaces with very poor ventilation or none.
As indicated by the experiments of Barnhart (1963) and Cantwell et al. (1973), dry ice can be used as a safe and inexpensive means of generating a gas for exterminating cockroaches in food service carts, as used, for example, in hospitals. These carts have many areas where cockroaches can hide and be inaccessible to sprays or dusts. Tompkins and Cantwell (1973) developed a dosage and time schedule for killing not only active stages, but also the eggs. The cart was centered on a 12 x 20-ft (3.7 x 6.1-m) sheet of black 6-mil plastic. Twenty pounds (9 kg) of dry ice was broken into pieces of appropriate size for placing at different levels in the cart. The plastic sheet was then drawn up and tied at the top. The volume of the enclosed cart was 71 cu ft (2 cu m). The level of carbon dioxide was monitored with a Gow-Mac Gas Analyzer at 5 and 24 hours. At 78 °F (26 °C), the minimum concentration of carbon dioxide required for the 24-hour period of the test was 21% in order to kill not only all the female German cockroaches with attached oöthecae that were used as the test insects, but also to prevent hatching of their eggs over the 30-day period of observation. This method of fumigation has the advantage of being safe and not requiring special training of personnel.
Boric acid powder is the least repellent of the insecticides tested. In buildings treated with boric acid, cockroaches will crawl over the deposits repeatedly. Although they do not die as rapidly as when treated with more toxic insecticides, few if any should be seen after a week or 10 days. Boric acid is inorganic, and in an area in which it can remain dry and is not likely to be removed, it will continue to kill cockroaches indefinitely (Ebeling et al., 1966, 1967, 1968; Moore, 1971, 1972). Before using, it must be passed through a sieve or screen to break up lumps and facilitate its passage through the usual dust applicators.
Sodium fluoride is likewise an inorganic powder, and is much more toxic to insects and to humans than boric acid, but it is highly repellent, and has been far less effective in control of cockroaches, both in laboratory devices utilized to simulate typical harborage areas in buildings (choice boxes, mockup wall voids, mockup closets) (Ebeling et al., 1967) and in experiments made in apartment buildings (Ebeling et al., 1968). As applied for cockroaches, boric acid is also effective for control of silverfish.
Boric acid acts in part as a contact insecticide, penetrating through,the insect's cuticle. In addition, cockroaches remove the dust from their antennae and legs while passing these appendages through their mouthparts. In this way, much dust is consumed,
