Reduced fecundity of Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae) following exposure of adults to methoprene

Experiments were carried out to determine whether exposure of Rhyzopertha dominica (F.) adults to wheat treated with methoprene affected their fecundity when subsequently transferred to untreated wheat. The juvenile hormone analogue methoprene is effective in controlling progeny of this species without killing parents. Therefore, there is the potential for adults to fly from treated grain and oviposit in untreated grain. Adult R. dominica were confined for 1-8 days to wheat that had been treated with methoprene at 0.01-4 mg kg(-1). After exposure the adults were transferred to untreated wheat for 7 days, and in some cases there was a second similar transfer. Exposure to methoprene for as little as 1 day resulted in reduced fecundity in the first week following exposure, and this reduction was related to dose. Fecundity was reduced by about a half following exposure to a dose of 2 mg kg(-1). Fecundity in the second week following exposure was not affected. The study shows that, as with some other insect growth regulators, there is a temporary reduction in fecundity of R. dominica adults after exposure to methoprene, Thus although methoprene can be expected to protect grain, parental insects flying from treated grain will be capable of infesting untreated grain or residues. (C) 1998 Elsevier Science Ltd. All rights reserved.