Effects of residual chlorfluazuron on haemolymph-borne oviposition-stimulating factors in Spodoptera litura

Acylurea insecticides can have various effects on insect reproduction and may even interfere with haemolymph‐borne oviposition‐stimulating factors (OSFs). This study describes the effects of injecting haemolymph into females of the common cutworm, Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), the effects of chlorfluazuron on the activities of OSFs, when sublethal doses (LD₁₀: 1.00 ng larva^?1 or LD₃₀: 3.75 ng larva^?1) were applied topically to newly ecdysed fifth instars under laboratory conditions. The haemolymph of moths of varying age, sex, and mating status resulted in the following increases in oviposition rates within the first 24 h, listed in decreasing order: the haemolymph of mated females injected into mated females (56%), mated females into newly emerged virgin females (53%), virgin males into virgin females (49%), and virgin females into mated females (29%), compared with uninjected mated or virgin females. Two factors are involved in the activation of ovipositon: OSF‐I is found in virgin females, whereas OSF‐II may be formed or received by males during mating. By contrast, the haemolymph taken from chlorfluazuron‐treated adults (treated as fifth instars with sublethal doses) injected into females resulted in the following percentage decreases in oviposition rates within the first 24 h, listed in decreasing order: the haemolymph of LD₁₀‐ and LD₃₀‐treated virgin males injected into untreated virgin females (77 and 84%, respectively), LD₁₀ and LD₃₀‐treated virgin females into untreated mated females (70 and 80%, respectively), LD₁₀ and LD₃₀‐treated mated females into untreated mated females (61 and 69%, respectively), LD₁₀ and LD₃₀‐treated mated females into untreated virgin females (59 or 68%, respectively), compared with untreated ones. Hence, residual chlorfluazuron decreases the activities of OSFs by significantly decreasing the oviposition rates. Moreover, virgin females’ or males’ OSFs are more sensitive to chlorfluazuron than those of mated cutworms. Both OSFs are most likely proteins.