Analysis of growth and development in the final instar of three species of predatory Coccinellidae under varying prey availability

摘要

For insects such as aphidophagous lady beetles, whose preferred food varies naturally in space and time, variation in adult body size is most likely a reflection of food acquired and allocated to growth by the final instar. We conducted a laboratory study to evaluate the nature of body size variation in Coleomegilla maculata (DeGeer), Harmonia axyridis (Pallas), and Hippodamia convergens Guerin-Meneville (all Coleoptera: Coccinellidae) by assessing how fourth instars respond developmentally to food deprivation. We also determined which growth functions best describe larval growth trajectories and evaluated whether these fourth instars regulate their growth based on initial body size. Access to food for a minimum of 1 day during the fourth stadium appeared to be a requirement for pupation in all three species. Putative critical weight for pupation falls within 10-14 mg for C. maculata, 13-16 mg for H. convergens, and 19-22 mg for H. axyridis, and development period after attaining the critical weight is not affected by food deprivation. The mixed-effect logistic function that accounted for individual and gender differences provided the best description of growth in the fourth instars of the three species. The reduced major axis regression revealed that growth in these lady beetles was convergent-regulated. The logistic growth trajectory, existence of critical weight, and determinate developmental response to food deprivation are traits that seem to suggest that fitness increase is attained by maximizing body size rather than survival in these beetles.