Asian Cockroach, Blattella asahinai
The Asian cockroach was first collected in North America in Kathleen, Fla., in 1986 (Brenner et al. 1988b). At the time of the discovery, this species was well-established, and was probably introduced into North America via the Port of Tampa (Florida) at least a few years earlier (Koehler et al. 1990). Since then, it has been detected in most parts of Florida and has the potential to extend its tange over a wide area of the southern United States (Atkinson et al. 1991a). For practical purposes, the Asian cockroach is identical in appearance to the German cockroach. Even the experts have difficulty determining whether a dead specimen is Asian or German (Koehler and Patterson 1987; Brenner et al. 1988b). Ross and Mullins (1988) compared oothecae and nymphs of Asian and German cockroaches. They found that although the egg case is smaller in the Asian cockroach, the size difference is due to smaller size of egg compartments rather than a reduced number. The nymphs of Asian cockroaches were smaller than German cockroaches, and Asian nymphs were pale along the margins of the abdomen, whereas the German cockroach nymphs were slightly pigmented.
In its native habitat in Asia, the Asian cockroach is rarely encountered and was only described in 1981. But in North America, it is free from its limiting factors and has the potential to become a major nuisance pest in suburban homes in the tropical and warmer temperate regions of North and South America.
The only truly reliable method of differentiating the two species was published by Carlson and Brenner (1988). They developed a method of analyzing cuticular hydrocarbons (the waxy layer of the exoskeleton) with gas chromatography. With this method, blind samples of Asian and German cockroaches were identified with 100% accuracy. Even legs, antennae, nymphs, and oothecae were identified with this technique.
The behavior of the Asian cockroach is very different from its cousin, the German cockroach. The Asian cockroach is an accomplished flier and lives in outdoor habitats, both feral and peridomestic. In contrast, the German cockroach is incapable of sustained flight and lives primarily indoors. The Asian cockroach can invade homes and become established. At dusk, this species becomes very active and adults are attracted to light reflected off light-colored walls, doorways, and windows. They then actively try to enter the home where they rest on lighted surfaces, such as lamp shades, television screens, and lighted walls. When lights are turned off as residents leave a room, the cockroaches will follow to the next lighted room. Thus, many residents may believe that these cockroaches are attacking them.
The Asian and German cockroach life cycles are similar to one another. (Atkinson et al. 1991a). Immature development in females took 67.8 days and 65.7 days in males. Females were much longer lived than males with adult longevity at 103.5 and 48.5 days, respectively. Female Asian cockroaches produce an average of 3.7 oothecae with 37.5 offspring in each. Ross and Mullins (988) indicated that oothecae from older females resulted in fewer offspring. The first oothecae is produced 13 days after becoming an adult with approximately eight days between subsequent oothecae. The female retains the oothecae for about 19 days and deposits it near the time of hatching. The Asian cockroach female can produce about 80 offspring in her lifetime which is significantly less than that of the German cockroach.
The Asian cockroach is only a pest during periods of peak adult populations (early spring and summer) in Florida. Some adults are present throughout the year. In the laboratory, the Asian cockroach will mate with the German cockroach and produce reproductively viable offspring which can fly. Such hybridization is rare among cockroaches and is an indication of the closely related nature of these two species (Ross 1992). These offspring also have the insecticide resistance of their German parent. Although this mating of species can occur in the laboratory, it seldom, if ever, takes place in nature due to the behavioral differences of the two species (Koehler et al. 1990).
This species has been observed feeding on various commercial agricultural crops such as lettuce, cabbage, roses, and strawberries. However, the Asian cockroach does not cause any major damage because commercial crops are routinely treated with insecticides for other pests. Therefore, damaging populations of Asian cockroaches in commercial plantings have not occurred (Koehler et al. 1990).
Asian cockroaches are primarily found outside in leaf litter and grassy areas. In areas found they tend to be the predominant cockroach species. In outdoor situations, in regions where it occurs, the Asian cockroach tends to be the predominant cockroach species. In certain areas of Tampa, Fla., more than 250,000 Asian cockroaches occur per acre (0.4 ha) in damp areas of heavy leaf litter, mulch under shrubbery, and in gardens.
The Asian cockroach is susceptible to all the commonly used insecticides (Koehler et al. 1990). Several scatter baits have been developed for control of Asian cockroaches and have provided successful control of populations. Because only a few Asian cockroaches enter a house at night, indoor applications of insecticides have been completely ineffective for control.