Egg size in Harmonia axyridis is a function of female age and body size

When allocating resources to reproduction, organisms face a trade-off between the size and number of their offspring. In insects such as lady beetles, maternal effects (e.g., female age and body size) can play a crucial role. Female coccinellids exhibit great variation in body size, largely as a function of variation in the food resources obtained as larvae, with delayed development and reduced adult size both resulting from food limitation. We studied the reproductive responses of Harmonia axyridis females that, as larvae, were provided access to food (eggs of Ephestia kuehniella) for either 30 minutes, six hours, or ad libitum daily. These treatments produced three different body sizes (small, medium and large) and parallel differences in developmental rate (slow, medium, fast). Observations on clutch size and egg size were made daily throughout adult life and both were correlated with female body size. Trade-offs between egg number and egg size were evident and there were changes in egg size with female age that were body size-dependent. In general, egg size increased in the initial stages of oviposition, then decreased slowly throughout the remainder of reproductive life, suggesting that females invest more heavily in progeny produced early in reproductive life than in those produced later.