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The Cockroach

The German cockroach is very successful at establishing an ecological niche in buildings and is resilient in the face of many pest control measures. Reasons include:

lack of natural predators in a human habitat

prolific reproduction

short reproductive cycle

the ability to hide in very small refuges

sexual maturity attained within several weeks, and

adaptation to and immunity from chemical pesticides

German cockroaches are thigmotactic, meaning they prefer confined spaces, and they are small compared to other pest species, so they can hide within small cracks and crevices that are easy to overlook, thereby evading humans and their eradication efforts. Conversely, the seasoned pest controller is alert for cracks and crevices where it is likely to be profitable to place baits or spray surfaces.

To be effective, control measures must be comprehensive, sustained, and systematic; survival of just a few eggs is quite enough to regenerate a nearly exterminated pest population within a few generations, and recolonization from surrounding populations often is very rapid, too.

Another problem in controlling German cockroaches is the nature of their population behavior. Though they are not social and practice no organized maternal care, females carry oothecae of 18-50 eggs (average about 32) during incubation until just before hatching, instead of dropping them as most other species of cockroaches do. This protects the eggs from certain classes of predation. Then, after hatching, nymphs largely survive by consuming excretions and moults from adults, thereby establishing their own internal microbial populations and avoiding contact with most insecticidal surface treatments and baits. One effective control is insect growth regulators (IGRs, hydroprene, methoprene, etc.), which act by preventing molting, thus prevent maturation of the various instars. Caulking baseboards and around pipes may prevent the travel of adults from one apartment to another within a building.

Female German cockroach with ootheca (the egg case of cockroaches, mantises, and related insects)

As an adaptive consequence of pest control by poisoned sugar baits, a strain of German cockroaches has emerged that reacts with glucose as distastefully bitter. They refuse to eat sweetened baits, which presents an obstacle to their control, given that baits are an economical and effective means of control. It also is a dramatic illustration of adaptive selection; in the absence of poisoned sweet baits, attraction to sugars strongly promotes growth, energy, and reproduction; cockroaches that are not attracted to sugars take longer to grow and reproduce, whereas, in the presence of poisoned sugared baits, sugar avoidance promotes reproduction.

Reproduction

The German cockroach reproduces faster than any other residential cockroach, growing from egg to reproductive adult in approximately 50 – 60 days.[14] Once fertilized, a female German cockroach develops an ootheca in her abdomen. The abdomen swells as her eggs develop until the translucent tip of the ootheca begins to protrude from the end of her abdomen, and by that time the eggs inside are full sized, approximately 1/4 inch long with 16 segments. The ootheca, at first translucent, soon turns white and then within a few hours it turns pink, progressively darkening until, some 48 hours later, it attains the dark red-brown of the shell of a chestnut. The ootheca has a keel-like ridge along the line where the young emerge, and curls slightly towards that edge as it completes its maturation. A small percentage of the nymphs may hatch while the ootheca is still attached to the female, but the majority emerge some 24 hours after it has detached from the female's body. The newly hatched 3mm-long black nymphs then progress through six or seven instars before becoming sexually mature, but ecdysis is such a hazardous process that nearly half the nymphs die of natural causes before reaching adulthood. Molted skins and dead nymphs are soon eaten by living nymphs present at the time of molting.