Seasonal variation in body size and male mating success within lichen tuft moths Izatha (Lepidoptera: Xyloryctidae)

Animals with scramble competition mating systems commonly exhibit female‐biased sexual size dimorphism, protandry and biased population sex ratios that reflect the active mate‐searching role of males. This is particularly so in many Lepidoptera, where males are classic scramble competitors. However, it is unclear how these features relate to the actual mating success of males or females over the reproductive season. In this study, patterns of adult flight period variation and mating status of the New Zealand lichen tuft moths Izatha peroneanella (Walker, 1864) and I. churtoni Dugdale, 1988 were determined from three locations. Protandry, male‐biased sex ratios and female‐biased sexual size dimorphism were evident in both species. There was a significant decrease in male and female I. peroneanella and I. churtoni body size over the flight period. Smaller males were more likely to have mated, but this was driven by the fact that they also emerged later in the breeding season, as collection date was the best predictor of mating status for males. Females exhibited higher likelihoods of having mated than males, but this was not influenced by body size. These data on the ecology and mating success of I. peroneanella and I. churtoni allow a better understanding of the mating system of species within this genus where their mating system is likely to be dominated by scramble competition under polygamy.