Life History

Cockroaches are paurometabolous insects. The immature cockroaches generally are similar in appearance to the adults except for their undeveloped sexual organs and lack of fully developed wings {Fig. 3,2). Reproduction in cockroaches is typically sexual, although parthenogenesis is reported in a few species. Comparative life history data for some of the more common cockroach pests are provided in Table I.

In cockroaches, embryogenesis and oviposition occur in one of three ways. Most species are oviparous, including all Periplaneta.species and the Oriental and brownbanded cockroaches. Eggs of oviparous species are protected inside a thick-walled, impermeable ootheca which is deposited soon after it is formed. Embryonic development occurs external to the femaie. The German cockroach is oviparous, but the female carries the ootheca protruding from the genital chamber until just hours before hatching occurs. The ootheca is softer than in Periplaneta species, allowing uptake of water and nutrients from the genital pouch. A few cockroaches, such as Blaberus species and the Surinam cockroach, are pseudo-ovoviviparous, in that females produce an ootheca which is extruded, rotated, and then retracted into the genital pouch. The eggs are incubated internally until hatching. The only known pseudo-viviparous species is Diploptera punctata, a pest species in Hawaii; the embryos hatch while still in the genital pouch. Embryogenesis takes 1—8 weeks, depending on the species.

The number of nymphal instars varies from 5 to 13, depending on the species, nutritional sources, and microclimate. Development of pestiferous species through the nymphal stadia requires from 6—7 weeks for German cockroaches to well over a year for Periplaneta species and other larger cockroaches. Typically, the nymphs exhibit strong aggregation tendencies, governed largely by aggregation pheromones. These pheromones act as locomotory inhibitors; when cockroaches perceive the pheromone they become relatively stationary. Studies of various species have shown that development to the adult stage is quicker when nymphs are reared in groups rather ft

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