Female mate choice and modulation of oviposition preference in the moth Spodoptera littoralis

Abstract: In this thesis, two aspects of reproductive behaviour in the Egyptian cotton leafworm, Spodoptera littoralis (Lepidoptera:Noctuidae) were studied. The first was whether female moths make a mate choice based on precopulatory assessments of male mating partners, and the second whether larval food plant experience of an ectoparasite modulates the female choice of oviposition site. The ejaculates of Lepidopteran males contribute with not only sperm, but also proteins and lipids. Certain characteristics such as body size and mating history have been shown to affect male ejaculate size in Lepidoptera. Female moths which can discriminate among males, and select mating partners providing larger ejaculates (spermatophores) would minimize mating costs associated with a high mating frequency. To assess if females make active mate choices, two-choice mating experiments were conducted. The female’s mate choice in the three following cases was evaluated; 1) virgin vs. recently mated males, 2) small vs. large males, 3) males reared on the same or different host plant as the female. Females were not shown to selectively mate with males based on any of the three studied characteristics. They did, however, mate with the most actively courting male. Male spermatophore size in relation to body size and mating status were also studied, and it was shown that large and virgin males contributed with larger spermatophores than small or once mated males. In host plant selection, the use of experience could be a way for generalist species to shorten decision time when presented with several host options. Adult females of S.littoralis normally show an induced oviposition preference for their larval host plant. In this study it was investigated if larvae reared on host plants in the presence of the mosquito Aedes aegypti instead would avoid oviposition on the larval food plant. This was examined in two-choice plant oviposition experiments. Female moths with mosquito experience did not show any avoidance of oviposition on the larval host plant.