Sublethal effects of chlorfluazuron on reproductivity and viability of Spodoptera litura (F.) (Lep., Noctuidae)

Abstract

Chlorfluazuron is an insect growth regulator for controlling the major insect pests in crops. To clarify the sublethal effects of chlorfluazuron on reproductivity and viability of common cutworm, Spodoptera litura, some experiments were conducted under laboratory conditions. The LD50 was found to be 12.0 ng/larva when evaluated up to pupation and 9.9 ng/larva up to adult emergence. At lethal dosages the development of different instars, moulting to pupae and emergence into adults were found to be more affected. Reduction in the body weight was also observed in the larvae and pupae when treated with a sublethal dose (LD30: 3.75 ng/larva) and in the adults when treated with sublethal doses (LD10: 1.00 ng/larva; LD30: 3.75 ng/larva) as newly moulted fifth instar larvae of S. litura, although the number of matings per female and life span of adult females and males remained unaffected by the same treatments. When sublethal doses were applied only to females or only to males, or both sexes, the average fecundity reduction was up to 35-44%. When only females were treated with sublethal doses, fertility was reduced by 49-58%; when only males were treated fertility was reduced by 65-81% and when both sexes were treated, fertility was reduced by 68-83%. Hatchability was reduced by 22-26% when only females were treated, by 44-66% when only males were treated and by 45-72% when both sexes were treated with LD10 or LD30 doses as newly moulted fifth instars. The results from these observations suggest that the fecundity was reduced to a similar degree when only females or only males or both sexes were treated with LD10 or LD30 doses as newly moulted fifth instars. However the fertility and hatchability were affected more when only males were treated with LD10 and much more when treated with LD30. Currently, work is in progress to find out the main reasons for the sublethal effects of chlorfluazuron on reproductivity and viability.