|Elliott, Norman - Norm|
Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2009
Publication Date: 5/1/2009
Citation: Phoofolo, M.W., Elliott, N.C., Giles, K.L. 2009. Analysis of growth and development in the final instar of three species of predatory Coccinellidae under varying prey availability. Entomologia Experimentalis et Applicata. 131:264-277.
Interpretive Summary: For insects like predaceous lady beetles, who feed on aphids, the quantity of the food they eat as larvae directly affects their biology, and hence their effectiveness as biological control agents. We conducted a laboratory study to determine how variation in body size of three species of lady beetle, Coleomegilla maculata, Harmonia axyridis, and Hippodamia convergens, was related to food intake during the larval stage. We did this by analyzing growth trajectories of fourth instars (large larvae), evaluating whether these fourth instars regulate their growth based on initial body size, and assessing developmental response to food deprivation. We found that the existence of species specific critical weights below which larvae always died, growth responses to food quantity, and developmental response to food deprivation were traits that maximize body size for species rather than survival. The importance of our finding is in contributing basic information on how species of lady beetle contend with food shortage in the field, and how it affects their biology and hence their ability at biological control of aphids.
Technical Abstract: For insects like aphidophagous lady beetles, whose preferred food naturally varies in space and time, variation in adult body size is most likely a reflection of food acquired and allocated to growth by the final larval instar. We conducted a laboratory study to evaluate the nature of variation in body size of Coleomegilla maculata (DeGeer), Harmonia axyridis (Pallas), and Hippodamia convergens Guerin-Meneville (Coleoptera: Coccinellidae) by analyzing growth trajectories of fourth instars and determining which growth function best described larval growth. We also evaluated whether these fourth instars regulate their growth based on initial body size, and assessed developmental response to 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. Access to food for a minimum of 1 day during the 4th 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 logistic growth trajectory, existence of critical weight, and determinate developmental response to food deprivation are traits that seem to emphasize fitness increase by maximizing body size rather than survival.