Lady beetle species have different microbial communities in their alimentary tracts – is it a diet effect?

Lady beetles (Coccinellidae) are polyphagus omnivores that employ a non-selective feeding strategy to optimize their energy and nutrient intake. Thus, the ability of coccinellids to realize a mixed diet might depend on the resource diversity within a habitat. To investigate how the habitat type affects the diet of coccinellids we analyzed their gut bacterial community. The majority of bacteria recovered from insect guts are likely transient organisms ingested with food. As a consequence, the gut bacterial diversity of coccinellidae may serve as an indicator of their diet diversity, and by extension, of resource availability within a local habitat. We hypothesize that high food diversity will be reflected by a higher richness of gut bacteria in coccinellids.

Specimens of four coccinellid species were collected during July 2012 in eight soy bean fields and eight prairies in southern Wisconsin. These habitat types represent a contrasting diversity of plants and associated prey for coccinellids. Each beetle’s gut was removed, and the gut bacterial community fingerprint was evaluated by automated ribosomal intergenic spacer analysis (ARISA).

An initial laboratory feeding assay supports the hypothesis that the diet of coccinellids alters their gut bacterial assemblage. From field collected beetles, we found that the gut bacterial community profiles were largely governed by species identity rather than habitat type and might indicate homogenous feeding habits at the species level. We speculate that the absence of the soy bean aphid in the hot summer of 2012 may have forced the beetles to consume greater amounts of alternative resources.