Submitted to: Journal of Insect Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 24, 2009
Publication Date: March 4, 2010
Citation: Lundgren, J.G., Weber, D.C. 2010. Changes in Digestive Rate of a Predatory Beetle over Its Larval Stage: Its Implications for Dietary Breadth. Journal of Insect Physiology. 56:431-437. Interpretive Summary: Omnivorous insects are an important source of pest management, but a critical consideration is how they divide their time between eating prey and non-prey foods (like pollen and fungus). We examined how larvae of the native lady beetle, Coleomegilla maculata, digests two types of prey (soybean aphid and Colorado potato beetle eggs) and two non-prey (corn pollen and yeast) foods by monitoring the amount of detectable food DNA in their stomachs over time. We found that C. maculata eats pollen more quickly as they get older, but it is not proportional to their size so that their consumption index (amount of food eaten per body size) goes down with age. C. maculata eats the same quantity of aphids, regardless of size, and their consumption index also diminishes with age. Except for aphid-fed larvae, older C. maculata larvae were more efficient at digesting the food than younger larvae. This improved digestive capacity indicates that this insect may be more efficient at digesting more types of food as they age. Thus, they may become more omnivorous as they age. The implications of this life history strategy to biological control of crop pests are discussed.
Technical Abstract: Prey and non-prey foods differ substantially in their suitability for zoophytophagous omnivores, but the relative quality of these foods depends on the stage-specific digestive capabilities of the organism in question. Quantitative (or real-time) PCR involving food-specific primer sets was used to measure consumption rates and digestion efficiencies of four foods- two prey (Aphis glycines and Leptinotarsa decemlineata eggs) and two non-prey (Zea mays pollen and the yeast Saccharomyces cerevisiae) species- over different larval stages of Coleomegilla maculata. The amount of Z. mays pollen consumed increased as larvae aged, but not proportionately with larval size, such that consumption indices decreased uniformly with insect age. While aging larvae fed A. glycines had a similar pattern in their diminishing consumption index, they consumed similar amounts of A. glycines DNA regardless of age, suggesting a negative feedback mechanism for consumption of this species of aphids. Older larvae digested three of the four foods significantly more efficiently than younger larvae, the exception being larvae fed A. glycines which was digested at a similar rate throughout the larval stage. There was a significant effect of time on detectability of food DNA for all four species of food. We conclude that C. maculata expands its physiological capacity for digesting prey and non-prey foods as they age in order to better accommodate the increased nutritional needs of the older larvae. This strategy has important implications for the life history strategies of zoophytophagous insects and how they function within foods webs.