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.LD₅₀ was estimated at 0.013 µg/larva.The
maximal weightsof 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.