László Varjas

Effects of the non-steroidal ecdysone mimic, RH-5849, on diapause and non-diapause larvae of the European corn borer, Ostrinia nubilalis Hbn.

Abstract Topical applications of the non-steroidal ecdysone mimic, RH-5849, as expected, initiated a premature moult in last larval instar of the European corn borer, Ostrinia nubilalis . However, RH-5849 induced a perfect supernumerary larval moult in diapause and non-diapause larvae when the application was performed very early in the instar. The compound induced larval-pupal intermediates and normal pupae if it was applied after 2 days in the last instar of non-diapause larvae and after 5–6 days in diapause larvae. The occurrence of larval-pupal moults and normal pupae demonstrated the onset of pupal commitment of the diapause larvae. Moulting to normal pupae was greatly improved by a double topical application of 1 μg RH-5849 onto diapause larvae. Although the rate of normal pupation was rather low, the ecdysone mimic could break the larval diapause of the European corn borer and produce normal pupae. From these results, the endocrine control of diapause induction is discussed.

Projuvenoids: Synthesis and biological evaluation of sulfenylated, sulfinylated, and sulfonylated carbamates

Applying the proinsecticide principle developed earlier for neurotoxic carbamate insecticides, a series of new N-sulfenylated, N-sulfinylated, and N-sulfonylated derivatives of fenoxycarb were synthesized and evaluated for juvenile hormone mimicking activity. Laboratory evaluations of the compounds using Pieris brassicae and Sitophilus oryzae, as well as field experiments using Bemisia tabaci, showed that several symmetrical biscarbamates with either a sulfenyl or sulfinyl bridge possessed higher activity than the parent carbamate. From the unsymmetrical compounds containing biologically inert derivatizing moieties, one of the sulfenylated biscarbamates also showed improved activity against P. brassicae. The changes in the biological activity of the sulfur-containing derivatives compared to that of the parent compound are attributed to the modified physicochemical characteristics, i.e., increased lipophilicity facilitating penetration, transport, as well as protection of the compound from metabolism.