Sublethal effects of Methoxyfenozide, in comparison to chlorfluazuron and beta-cypermethrin, on the reproductive characteristics of common cutworm Spodoptera litura (fabricius) (lepidoptera: noctuidae)

Abstract

The sublethal effects of Methoxyfenozide on reproductive bio-characteristics, viz., fecundity, fertility and oviposition were evaluated on Spodoptera litura treated as 2nd (L2) and $5^ {th}$ instars (L5) larvae with sublethal doses of methoxyfenozide, corresponding to the $LC _{10}$ and $LC _{30}$, and compared with the effects induced by chlorfluazuron and beta-cypermethrin. In case of L2 treatment, the results elucidated that $LC _{10}$ of methoxyfenozide and chlorfluazuron significantly (P<0.05) reduced the fecundity and fertility as compared to beta-cypermethrin and the control. Moreover, due to $LC _{30}$ of methoxyfenozide, the total egg laying and hatching rate were also significantly (P<0.05) reduced by the three pesticides as compared to the control. $LC _{10}$ of methoxyfenozide, chlorfluazuron and beta-cypermethrin could not induce any significant effect on pre-oviposition and oviposition duration. Further, it was noticed that $LC _{10}$ of methoxyfenozide and chlorfluazuron significantly reduced oviposition duration as compared to beta-cypermethrin and control. When $LC _{10}$ was used for the 5th instar larvae, the total number of eggs was markedly reduced by methoxyfenozide and chlorfluazuron as compared to beta-cypermethrin and the control. Likewise, the hatching rate was significantly (P<0.05) reduced with respect to all pesticides. Further at $LC _{30}$ concentration, the same trend of insecticidal impact was noticed on fecundity and fertility response of all the tested insecticides. The results revealed that the experimental insecticides at $LC _{10}$ had no significant effect in both pre-oviposition and oviposition duration in comparison with control, while only oviposition duration was significantly reduced at the higher concentration of ($LC _{30}$) for methoxyfenozide and chlorfluazuron. It is possible to conclude that the effects of methoxyfenozide with its sterilizing properties if used strategically on S. litura might induce changes in population dynamics of this pest in vegetable crops and it may be considered potent insecticidal compound for controlling this pest.