Male larval nutrition in Choristoneura rosaceana (Lepidoptera: Tortricidae): an important factor in reproductive success

This study examines how Choristoneura rosaceana male quality, as determined by larval diet, age and mating history, affects the reproductive success of both sexes. While the size of the spermatophore produced at first mating increased linearly with male age, the frequency of mating was significantly higher for middle-aged males (2–4 days old) than younger (0–2 days old) or older (6–8 days old) individuals, when both sexes were fed on artificial diet. However, the duration of copulation was longer in couples with older than younger males. The observed age-related changes in spermatophore size had no significant effect on female longevity, fecundity or fertility, suggesting no direct relationship between male investment and spermatophore size under these experimental conditions. Different larval food sources (artificial diet, maple and hazelnut) did not affect the proportion of 2-day-old virgin males that mated; however, the proportion that remated was significantly higher for males reared on high-quality food (maple and artificial diet) than those on hazelnut, a poorer food source. There was a 5-fold decline in spermatophore size between the first and second matings on all diets, but female reproductive output was reduced by only 25%. In contrast, while the first spermatophore produced by males on hazelnut was 1.5 times smaller than those produced on maple and artificial diet, the fecundity of their mates was 40% less than those mated with high-quality virgin males. These results provide additional support to the idea that spermatophore size is not a valuable indicator of male quality. Most tethered females placed in the field during the first flight period mated with virgin males (based on the size of the spermatophore), suggesting that female choice exists in this species. These results are discussed in relation to the incidence of polyandry in naturally occurring populations of Choristoneura and the potential use of size and/or chemical cues by females to assess male quality.