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Chlor¯uazuron is an insect growth regulator for controlling the major insect pests in crops. To clarify the sublethal effects of chlor¯uazuron on reproductivity and viability of common cutworm, Spodoptera litura, some experiments were conducted under laboratory conditions. The LD 50 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 (LD 30 : 3.75 ng/larva) and in the adults when treated with sublethal doses (LD 10 : 1.00 ng/larva; LD 30 : 3.75 ng/larva) as newly moulted ®fth 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 LD 10 or LD 30 doses as newly moulted ®fth 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 LD 10 or LD 30 doses as newly moulted ®fth instars. However the fertility and hatchability were affected more when only males were treated with LD 10 and much more when treated with LD 30. Currently, work is in progress to ®nd out the main reasons for the sublethal effects of chlor¯uazuron on reproductivity and viability. U. S.

Summary This paper describes the physiological mechanism of action of chlorfluazuron on testicular development and spermatogenesis when sublethal doses (LD10: 1.00 ng/larva or LD30: 3.75 ng/larva) are applied topically to the cuticle of newly moulted fifth instars of the common cutworm Spodoptera litura (F.) (Lepidoptera, Noctuidae). These doses disrupt the growth and development of testes by decreasing the volume and weight of testes and thickness of testes sheath as compared with that of the controls. Sublethal doses of chlorfluazuron also significantly reduce the protein content of the testis, but do not affect the carbohydrate and lipid contents in newly emerged treated males when measured in μg/mg of testis as compared with that of the controls. Additionally, such doses disrupt spermatogenesis by reducing the number and size of eupyrene and apyrene sperm bundles in the testis. Very few or no eupyrene sperm bundles are observed in vas deferens of pre‐ and newly moulted adults compared with controls. This result shows that the transfer of sperm bundles from testes to vas deferens is delayed in treated males. The effects of chlorfluazuron on testicular development and spermatogenesis is thought to be one of the factors responsible for the reduction in fecundity, fertility and hatchability caused by sublethal doses of chlorfluazuron.

Sublethal doses (LD10: 1.00 ng larva -1 ; or LD30: 3.75 ng larva -1 ) of chlorfluazuron were applied topically to the cuticles of newly moulted fifth instars of the common cutworm, Spodoptera litura (F.) (Lepidoptera, Noctuidae). During mating, the treated males transferred spermatophores of a significantly lower weight into females. The weight of spermatophores transferred by LD30-treated males was significantly lower than the weight of spermatophores transferred by LD10-treated males, which was in turn significantly lower than the weight of spermatophores transferred by untreated males. The transfer of spermatophores was delayed by 5-15 min in LD10-and LD30-treated males. However, mating duration was not affected by chlorfluazuron treatment. The transfer of spermatozoa was also delayed by 5-10 min in LD10-and LD30-treated females. Polygynous male adults mated an average of ten times during their lifespan of 11-13 days when paired every day with a new virgin female of the same age. The number of matings per polygynous male was not affected by chlorfluazuron treatment, but the first mating was delayed by 1 day. The number of inseminated sperm found in the spermatophore averaged 10.3 (Ϯ 2.1) ¥ 10 5 over the lifespan of a male, in which the number of eupyrene sperm was 5.4 (Ϯ 1.1) ¥ 10 5 . The number of inseminated eupyrene sperm decreased by 66% and 88%, respectively, in LD10-and LD30-treated males. No significant reduction in the number of inseminated eupyrene sperm was observed when females were treated with LD10 or LD30 doses, nor was there a significant reduction when both sexes were treated with the LD10 or LD30 doses relative to treatment of males with the same doses. The ratio of inseminated eupyrene to apyrene sperm was not affected by chlorfluazuron treatment.

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