Blattella asahinai, the Asian cockroach, is a species of cockroach that was first described in 1981 from insects collected on Okinawa Island, Japan. It is a small species of cockroach, typically long and tan to dark brown in colour with dark parallel stripes on the back of their heads. It is commonly mistaken for the German cockroach (B. germanica) due to their similar appearance. It is now commonly found in the United States in and around houses.
Characteristics and appearance
The Asian cockroach is nearly identical to the German cockroach (B. germanica) except for a few minor morphological differences. Like the German cockroach, it is about long, is tan to brown in color, and has wings. However, its wings are longer than the German cockroach, and a difference is seen in a groove in the abdomen in the two species. The quickest way to tell the difference between them is that the Asian is a strong flyer and is attracted to light, unlike the German. To differentiate between the two cockroaches with the naked eye, there are noticeable parts of each cockroach. The ventral surface of the left mandible, the vein coloration of the right tegmen, the wing size and venation as well as the setal marginal bristles on the cerci are the slight morphological differences between the Asian and German. Recent genetic analyses indicate that B. germanica only diverged from B. asahinai slightly over 2000 years ago, presumed to be the point at which the German cockroach spread to areas where it was no longer in contact with B. asahinai.
The first reported appearance of the Asian cockroach in the United States was in 1986 in Lakeland, Florida but at first it was believed to be the German species. It is believed that the Asian came to Florida through the import of goods from Japan. On March 3, 1986, Dr Louis M. Roth received cockroaches of Lakeland, Florida from Dr Philip G. Koehler of Florida Extension Services of the University of Florida for inspection. where they tested the two species through an ethological, morphological and genetic approach in order to confirm the presence of the Asian cockroach in Harris County, Texas. Evaluations of DNA gene sequences showed similarities to the German.
Habitat and behaviour
Asian cockroaches are predominantly found outdoors in shaded mulched, composted areas where fresh plant litter accumulates as well as in damp areas. Its population reaches its zenith in late August and declines rapidly with the onset of cool weather. Asian cockroaches are the most active at dusk and are attracted to light-coloured surfaces and bright lights. This means at dusk, the Asian cockroach may fly towards the home and enter through open doors and windows but indoor invasions occur rarely. While other cockroaches carry diseases and bacterium, as of today, research has not suggested that the Asian cockroach carries any pathogens or diseases. However, they do come into contact with other bacteria due to their habitat preferences being around homes with outdoor pathogens, animal feces, and fungi. During adverse weather conditions such as cold weather or dry conditions, the Asian cockroach burrows down into the leaf litter.
Diet
Asian cockroaches are omnivorous, as are most cockroach species : they will eat anything they can find. They have been observed to eat human food, pet food, flowers and agricultural crops, as well as prey such as lepidopteran eggs in soybean and cotton crops. They have also been sighted feeding on lettuce, cabbage, and strawberries.
German cockroach comparison
The Asian cockroach is the presumed ancestor of the German cockroach, the predominant cockroach pest in America and some parts of the world. and to move around compared with the German cockroach, which can be rarely seen flying, merely fluttering its wings ineffectively. The other main difference between the two species is its reaction to light sources; the Asian cockroach is naturally attracted to light, whereas the German cockroach scatters away in the presence of bright light.
Reproduction and life cycle
Asian cockroaches and field cockroaches are similar ecologically in comparison to the German cockroach due to both these species breeding outdoors. Both the female Asian and German cockroach carry their egg capsules (oothecae) with them until the eggs hatch but female Asian cockroaches produces fewer oothecae in comparison to the German cockroach, producing approximately four oothecae in their lifetime, each averaging 35 - 40 eggs. The Asian cockroach is most fertile from February to May as well as in August through to September. Asian cockroach females requires 60 - 70 days to become an adult, slightly longer than the males. The lifetime of male and female Asian Cockroaches are approximately 50 and 100 days respectively, compared with the German cockroach which lives on average 130 for males and 150 days for females.
Beneficial insect
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In 2006, entomologist Robert Pfannenstiel conducted research on the ecology of predators of crop pests in Texas, in particular the Asian cockroach. Asian cockroaches ventured west into Texas in 2006, and became the most common predator of bollworm eggs in the state's Rio Grande Valley region. The bollworm threatens cotton, soybean, maize, and tomato crops. Helicoverpa zea (Boddie) and Spodoptera exigua (Hubner) are leading pests of soybean crops in Southern Texas. Their eggs were placed on the leaves of soybean crops, without pesticides, and were observed in 3-hour increments over 24 hours to observe both the night and day behaviour of predators towards the pests of the crops. From 2001 to 2005 similar tests were conducted on the predation of Lepidopteran eggs but no observations of the Asian cockroach were made. In 2006, nymph and adult Asian cockroaches were observed feeding on H. zea and S. exigua from both the canopy and leaf litter of the crops and made up 53.7% of all predators feeding on the eggs. Scatter baits have been purposely developed for the control of the Asian cockroach and have proven to be effective whereas indoor applications of insecticides have proven to be ineffective.