The most important of the several reasons for considering some cockroaches to be pests is based on the species that invade people's homes and other buildings and become very numerous. Most people find such infestations to be objectionable, in part because the important pest species also have an unpleasant odor and soil foods, fabrics, and surfaces over which they crawl. However, on a worldwide basis less
than 1% of all known cockroach species interact with humans sufficiently to be considered pests. The actual number varies depending on location, because some pest species are greatly restricted in their global distribution. It is also true that more pest species are encountered in tropical locations than in the colder parts of the world. Of the 25 to 30 species that can be a problem, more than half are only occasionally of importance and should be rated as minor or even incidental pests. Of the remaining species, only four or five are of global importance as pests, with the other nine or ten species having regional significance only.
The most important pest species is the German cockroach, Blattella germanica (Blattellidae) (Fig. 1). It has a worldwide distribution and can survive well in association with any human habitation that provides warmth, moisture, and food. It is small, measuring 10 to 15 mm in length. Adults are yellowish-tan but nymphs are black, with a light-colored stripe up the mid-dorsum. There are two longitudinal, black, parallel bands on the promotum of both nymphs and adults. The wings cover most of the body in adults of both sexes. This is a nocturnal species that lives mainly in kitchen and bathroom areas. When a person enters the kitchen of an infested house at night and turns on a light, the cockroaches scurry out of sight—a startling experience that adds to the desire to eliminate them. There are three or four generations per year. Each egg mass (ootheca) contains from 30 to 50 eggs, and each female can produce three to six oothecae. The potential for rapid population expansion is obvious.
The oriental cockroach, Blatta orientalis (Blattidae) (Fig. 2), the next most important pest species, is restricted to the more temperate regions of the world. It is large, measuring 20 to 27 mm in length. All stages are dark brown to black. Females are essentially wingless, but in males the wings cover about two-thirds of the abdomen. This cockroach frequents basements and crawlspaces under buildings, where temperatures are cooler, and often lives outdoors. It is a long-lived insect and may require 1 to 2 years to complete its life cycle. The ootheca contains 16 eggs, and one female may produce eight
or more oothecae. Under favorable conditions B. orientalis can become very numerous.
There are five or six species belonging to the genus Periplaneta (Blattidae) (Fig. 3) that are important pests. The American cockroach, P. americana, is the most notorious. It measures 35 to 40 mm in length and is a chocolate-brown color in all stages. Adults of both sexes are fully winged and may undertake a weak flight. P. americana is widely distributed around the world but does not extend into the temperate zones as far as does the German cockroach. It requires 6 to 9 months to complete its life cycle. Among other Periplaneta species of importance are the Australian cockroach, P. australasiae, the smoky-brown cockroach, P. fuliginosa, and the Japanese cockroach, P. japonica. Each has a more restricted distribution, with P. japonica, for example, being found in Japan and China. They are all large cockroaches with a long life cycle but can become numerous under certain conditions. Although tending to be outdoor cockroaches, they often occupy buildings in which food is stored, prepared, or served.
The brown-banded cockroach, Supella longipalpa (Blattellidae) (Fig. 4), is a nearly cosmopolitan pest. It is small,
measuring 10 to 14 mm in length. As its common name indicates, there are two dark, transverse stripes or bands on the dorsum. The pronotum lacks the two black bands found on the German cockroach. Nymphs are light colored. Females produce numerous oothecae and glue them in inconspicuous places. Each one has about 16 eggs. The life cycle requires approximately 3 months to complete. This cockroach occupies homes and other buildings but unlike the German cockroach is not restricted to the kitchen and bathroom.
Other pest species include the Turkistan cockroach, Blatta lateralis (Blattidae), two species in the genus Polyphaga (Polyphagidae), the Madeira cockroach, Rhyparobia maderae (Blaberidae), the lobster cockroach, Nauphoeta cinerea (Blaberidae), the Suriname cockroach, Pycnoscelus surinamensis (Blaberidae), the Asian cockroach, Blattella asahinai (Blattellidae), the harlequin cockroach, Neostylopyga rhombifolia (Blattidae), and the Florida cockroach, Eurycotis floridana (Blattidae). Most of these species are of regional concern as pests.
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