Effect of 20-hydroxyecdysone agonist, tebufenozide, on pre-and post-diapause larvae of Dendrolimus pini (L.) (Lep., Lasiocampidae)

Abstract

Studies of the effects of a novel insect growth regulator (tebufenozide, RH 5992) in pest lepidopterans are extended to its influence on pre- and post-diapause larvae of the pine-tree lappet, Dendrolimus pini (L.) (Lep., Lasiocampidae). Larval diapause was induced under experimental conditions. The relation between the width of head capsule and each larval instar of the experimental populations is presented. The toxicity of tebufenozide applied topically and per os (orally), and its effects on feeding activity were examined. High doses and concentrations (≥ 100 ng/larva and ≥ 0.001%) of tebufenozide were toxic and reduced the feeding intensity in larvae of D. pini, however, post-diapause larvae were less sensitive to oral treatment with tebufenozide then pre-diapause insects. In pre-diapausing insects of the fourth instar a greater than four-fold fall in mortality was observed among the insects treated with low doses/concentrations (0.1-10 ng/larva and 0.00001%-0.001%, respectively). A remarkable stimulatory effect on feeding behaviour was observed in pre-diapausing IV instar larvae when treated with tebufenozide topically, in a dose of 10 ng/larva. A possible ecdysteroid mimicking effect of tebufenozide onto feeding and mortality among diapause-destined D. pini is discussed.