PHYSIOLOGICAL EFFECTS OF THE JWENOID PYRIPROXYFEN ON ADULTS, EGGS, AND LARVAE OF THE CAT FLEA

Abstract:
Adult cat fleas often survive several weeks without feeding. However, when newly emerged adults were maintained on filter paper treated with pyriproxyfen at 1.1 pg/cm, they lived only 8 days, compared with low mortality in the controls. Dying fleas examined histologically showed evidence of fat body depletion and midgut distention with air suggesting that death might be due to starvation. This finding was consistent with the hypothesis that unfed fleas undergo an adult diapause caused by failure of the corpora allata to release juvenile hormone (JH). However, subsequent experiments did not support this hypothesis. Exposure of unfed fleas to residues of JH 111 did not cause mortality, and fed fleas maintained on pyriproxyfen-treated dog hair died at the same rate as unfed fleas maintained on treated filter paper. Studies involving flea eggs suggested that pyriproxyfen is less effective as an ovicide than fenoxycarb. Marchiondo et al. (1990) showed that newly laid eggs exposed to fenoxycarb treated filter paper for 60 seconds failed to hatch. Pyriproxyfen exposure of newly laid (14 hour-old) eggs to the same dose rate did not prevent hatching. However, 10 minute exposure of eggs to pyriproxyfen killed 50% of the fleas that developed to the larval stage. Thus pyriproxyfen had an unusual latent effect in which short-term exposure of flea eggs early in embryogenesis was often lethal to larvae that hatched from the egg 3 days later. In contrast, longer-term (2 hour) exposure of eggs to pyriproxyfen caused embryocidal effects.