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

Abstract

The Egyptian cotton leafworm, Spodoptera littoralis, is destructive pest of cotton and various crops in Egypt and some parts of the world. The present study was carried out aiming 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 newly moulted last instar larvae. cycloheximide exhibited toxic effect on larvae, pupae and adults. Unexpectedly, no mortality was observed at the highest dose. LD 50 was estimated at 0.013 µg/larva. The maximal weights of the treated larvae increased and the larval growth was remarkably enhanced. The larval and pupal durations were shortened. Some larvae appeared as 'giant larvae', only at the lower two doses. They enlarged in size and appeared heavier than other treated and control larvae. They survived 2-times longer period than of the control larvae and perished without pupation. Topical treatment of larvae only with the lower two doses induced a state of suspended development, 'permanent prepupae' which failed to pupate. Cycloheximide exerted an inhibitory action on the pupation rate after treatment only with the lower three doses. Some deformed pupae were produced. The adult emergence was considerably blocked at lower three doses. The oviposition was completely prevented, at the higher two doses, but partially inhibited at the lower two doses. No fecundity could be determined at the higher two doses because no oviposition was carried out. At the lower two doses, fecundity was dramatically reduced. All eggs failed to hatch indicating complete sterility of S. littoralis.