Interaction pathways between Diptera and coccinellid larvae: Evidence from an antibody-based detection system

The prey range of many generalist predators is frequently unknown outside of laboratory studies and there are relatively few methods, eg. direct observations and gut dissections, available to decipher food selection behavior of insects in the field. This study examined dipteran consumption by predatory coccinellid larvae in alfalfa using a dipteran-specific monoclonal antibody and enzyme-linked immunosorbent assays. To estimate prey choice and the potential for selective foraging, the presence of dipteran antibodies was correlated with the available prey levels in the field. We determined the decay rate of dipteran proteins under laboratory conditions and, due to the design of the monoclonal antibody; proteins were not detectable in coccinellid larvae beyond 5 h. Therefore, positive results obtained from field-collected larvae indicate recent predation events. The proportion of field-collected larvae positive for dipteran proteins differed based on species, instar, and sampling date. Positive tests were obtained for 3rd and 4th instars of three coccinellid species (Coccinella septempunctata 8% of 113 larvae, Coleomegilla maculata 3% of 112 larvae, and Harmonia axyridis 7% of 14 larvae). The proportion of larvae testing positive for dipteran antibodies was greatest during the first growth of alfalfa (April – May), when aphids were most abundant. Dipteran predation by coccinellid larvae may be related to dietary mixing or optimal feeding on herbivorous or predaceous dipterans. Because the dipteran antibody used in this study is order-specific, studies are needed to determine which Dipteran groups are being fed upon by these larval stages of coccinellids.