Note: Transovarial activity of the chitin synthesis inhibitor novaluron on egg hatch and subsequent development of larvae ofTribolium castaneum

Abstract

The effects of the chitin synthesis inhibitor (CSI) novaluron on egg hatch and on larval development ofTribolium castaneum (Herbst) concentrations of 1.0, 0.3, 0.2 or 0.1 ppm were tested. The effect of novaluron at low concentrations depended strongly on the exposure period. At 0.3 ppm, egg hatch ofT. castaneum was totally inhibited after 28 days; at 0.2 ppm the effect was much less but inhibition increased progressively to 66% in the 35-day experiment; at 0.1 ppm novaluron was ineffective. The viability of the larvae that hatched from the laid eggs and developed on untreated flour was also dependent on concentration of novaluron and exposure time: exposure ofT. castaneum adults to novaluron-treated flour at 0.3 ppm for 8 days, or at 0.2 ppm for 36 days, caused 100% or 97.5% mortality, respectively. At both 0.3 and 0.2 ppm, larval deaths were mainly in the first instar. Exposure ofT. castaneum adults to treated flour may serve as a good model for evaluating the effect of CSIs on internal feeders, especiallySitophilus oryzae (L.). The present study contributes to our understanding of CSI transovarial activity against internal stored product coleopterans whose larval stage develops inside the grain without contact with the toxicants.