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Keywords:

  • apyrene sperm;
  • eupyrene sperm;
  • LD10;
  • LD30;
  • newly moulted fifth-instar;
  • polygyny;
  • sperm decrease;
  • spermatheca

Abstract

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 (± 2.1) × 105 over the lifespan of a male, in which the number of eupyrene sperm was 5.4 (± 1.1) × 105. 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.