Impairment of Development and Reproductivity of the Egyptian cotton leafworm Spodoptera littoralis Boisduval (Noctuidae: Lepidoptera) by Cycloheximide.

Abstract

The Egyptian cotton leafworm, Spodopteralittoralis, is destructivepest of cotton and various crops in Egypt and someparts of the world. The present study was carried outaiming to assess the disruptive effects of cycloheximide on survival, growth,development, metamorphosis and reproductive potential of this pest. Four doses:180, 120, 60 and 30 µg/larva had been topically applied (once) onto the newlymoulted last instar larvae. cycloheximide exhibited toxic effect on larvae,pupae and adults.Unexpectedly, no mortality was observed at the highestdose.LD50 was estimated at 0.013 µg/larva.Themaximal weightsof the treated larvae increased and the larval growthwas remarkably enhanced. Thelarval and pupal durations were shortened.Some larvae appeared as'giant larvae', only at the lower two doses.They enlarged insize and appeared heavier than other treated and control larvae. They survived2-times longer period than of the control larvae and perished without pupation.Topical treatment of larvae only with the lower two doses induced a stateof suspended development, 'permanent prepupae' which failed to pupate.Cycloheximideexerted an inhibitory action on the pupation rate after treatment only with thelower three doses. Some deformed pupae were produced. The adult emergence wasconsiderably blocked at lower three doses.The oviposition wascompletely prevented, at the higher two doses, but partially inhibited at thelower two doses. No fecundity could be determined at the higher two dosesbecause no oviposition was carried out. At the lower two doses, fecundity wasdramatically reduced. All eggs failed to hatch indicating complete sterility ofS. littoralis.