2012 Annual Report
1a.Objectives (from AD-416):
Investigate the contributions of symbiotic gut bacteria to the feeding ecology of carabid beetles and crickets. Specifically, substantiate which bacteria facilitate granivory of weed seeds by these insects and how environmental, phylogenetic, and physiological factors constrain these relationships.
1b.Approach (from AD-416):
Feeding assays and insect collections from cropland will be used to identify the effects of specific bacterial constituents of the community that contribute to seed digestion. Bacterial culture methods will be combined with PCR-based methods to identify and isolate bacterial communities from carabid and cricket guts from cropland in our region. Experimental endpoints that will be assessed include seed consumption rates and the relative digestibility of seeds by the insects.
Two laboratory experiments were conducted to further understand the role of gut microbes on the feeding behavior of omnivorous insects. The first experiment aimed to resolve the importance of Enterococcus faecalis on seed consumption by Harpalus pensylvanicus. Four treatments were established (each with approximately 30 individuals). The first two treatments were fed antibiotics, and one of the treatments received E. faecalis. The second two treatments received no antibiotics, and one of these treatments received E. faecalis. Seeds were fed to H. pensylvanicus, then the antibiotics were administered (or a control diet) for 10 d to remove the microbial community from the beetle guts. Seeds were again fed to the beetles. Finally, the E. faecalis (or a control diet) were fed to the beetles, followed by a final quantity of seeds. After each seed-feeding, seed consumption rates and various feeding metrics (efficiency of converted digested material, efficiency of converted ingested material, and approximate digestibility) were measured for each treatment. Enterococcus faecalis increased seed consumption rates by 40%, but only if the beetle had received antibiotics. This work clearly shows that E. faecalis contributes to granivory rates in omnivorous beetles, and suggests that resident bacterial communities affect the ability of E. faecalis to function.
The second experiment investigated how antibiotics affect the dietary preferences of the cricket, Gryllus pennsylvanicus. Prey (moth eggs) and seeds (lambsquarters) were offered under choice conditions to crickets that had received antibiotics or not (n = 30, each). The quantity of each food was subsequently measured, as were various feeding efficiency metrics. The experiment has been completed, but the data awaits analysis.