German cockroach's are the most economically important urban pest in the United States and throughout the World. It is the most common cockroach species in houses, apartments, restaurants, hotels and other institutions. |
The German cockroach is the most commonly encountered of the house infesting species in the United States. It is also generally the most persistent and difficult to manage. The reasons for this are somewhat complex, but an understanding of some of the factors involved is basic to the practice of pest management. First, the German cockroach has a larger number of eggs per capsule than the other species that infest structures. Second, it also has the shortest period to develop from hatching until sexual maturity; thus, populations of German cockroaches will build up faster than other species. These factors combine to produce what entomologists call a "high reproductive potential.
Third, German cockroach nymphs have a better chance of surviving than do other species because the female carries the egg capsule during the entire time that the embryos are developing within the eggs. This results in the nymphs avoiding many hazards of the environment which may affect eggs that remain detached and isolated. Thus, more nymphs are likely to hatch, and a higher reproductive potential is likely.
Fourth, German cockroach nymphs are smaller than most other cockroaches; thus, they are able to conceal themselves in many places which are inaccessible to individuals of the larger species. In fact, in a commercial kitchen, there may be literally thousands of cracks and crevices young cockroaches can hide in and remain protected. German cockroach nymphs also tend to stay close to each other, often close to the female at the time of hatching, creating a tendency for a high local population density. They also have aggregation pheromones associated with their droppings, which have the effect of increasing the level of aggregation or clumping of individuals in the population.
These biological factors, combined with its very adaptive feeding habits and other behaviors, give the German cockroach advantages toward increased chances for survival and persistently maintaining high populations.
Moreover, there are additional factors which contribute to the success of the German cockroach. The "high reproductive potential" of this species can significantly affect its ability to develop resistance to insecticides. During the late 1950s and the 1960s, insecticides such as DDT and chlordane were widely used to control German cockroaches. In many cases, some individuals of German cockroach populations exposed to these insecticides survived. And because these cockroaches reproduce so quickly, survivors were able to pass the ability to survive exposure to DDT and chlordane to following generations. Over many generations, large portions of populations can then become resistant to insecticides. It is possible within a single town or city to find both populations of cockroaches that are resistant to a particular insecticide and others that are susceptible to the same insecticide. Each population's history of insecticide exposure over many generations will determine the levels of resistance to various insecticides.
The German cockroach is a relatively active species, moving around readily within structures. They travel from one location to another and can pass through very small openings. They are also regularly carried from place to place in such things as bagged potatoes and onions, beverage cartons, grocery bags, food cans, other food packages, handbags, and the folds of clothing. The pest management professional must look very closely to find all the places in which cockroaches may be living, and try to determine how cockroaches might be transported into the premises. It may not be possible to eliminate all the German cockroaches in a structure at any one time if a steady flow of cockroaches is carried into the premises via people, food shipments or other routes. Further, the use of insecticides may scatter cockroaches widely throughout a building. If all of the scattered or "satellite" populations are not found and treated, re-infestation of treated areas will occur.
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