Long-term effects of fenoxycarb upon reproductive activity and fecundity in adult female Periplaneta americana

Abstract

Adult, female Periplaneta americana were topically treated with between 1.25–100 μg of fenoxycarb and their reproductive activity was subsequently monitored for 6 months. Doses of ≥ 2.5 μg of fenoxycarb significantly increased oötheca production for up to 4 weeks, but from about the tenth week onwards these animals tended to produce fewer oöthecae than controls so that the total number of oöthecae laid during the 6 months was not significantly changed by treatment. Treatment of insects with 100 μg of fenoxycarb markedly reduced the numbers and weights of nymphs emerging from oöthecae laid during the first 4 weeks after treatment. Hatching and nymph weight were still significantly reduced in oöthecae laid 12–13 weeks after treatment, but by the end of the 6 months there was no difference from controls. All the nymphs successfully moulted into apparently normal second-instar larvae. Corpora allata were isolated from insects 13 weeks after treatment with 100 μg of fenoxycarb. When incubated in vitro, they showed significantly reduced rates of juvenile hormone biosynthesis compared with glands from control insects.