Effects of early growth conditions on body composition, allometry, and survival in the ladybird beetle Harmonia axyridis

During both the larval and adult stages, the ladybird beetles Harmonia axyridis (Pallas, 1773) feed primarily on aphids, populations of which may fluctuate dramatically in time and space. Harmonia axyridis were reared under three resource treatments: high, low, and improving. We predicted that beetles experiencing consistently poor larval conditions would allocate limited resources to dispersal traits (by increasing relative wing surface area and fat storage), whereas larvae facing good or improving conditions were predicted to allocate preferentially to reproductive traits. As predicted, beetles reared at low food had lower wing loading and stored more fat than individuals reared at consistently high food. When conditions were initially poor but improved during development, body size was reduced relative to the high food treatment, though wing area scaled similarly. Allocation of fat and protein was dependent on both sex and treatment. Females in improving conditions stored less fat, and males less protein, relative to low food conditions. This is suggestive of a trade-off between reproduction and dispersal that is resolved differently between the sexes. Unexpectedly, adult survival under starvation was not appreciably affected by larval growth conditions, although males lived about 10 days longer, on average.