Host acceptance behavior in the soybean aphid parasitoid Binodoxys communis (Hymenoptera: Braconidae) - the role of physiological state in biological control.

Abstract

Host choice behavior in insect parasitoids and herbivores has been predicted to vary dynamically in response to external and internal factors acting on a foraging female; physiological state and egg load in particular have been shown to play a major role. In my dissertation, I addressed the role of physiological state in parasitoid host choice behavior at the host species level under field conditions. The parasitoid of choice was the classical biological control agent Binodoxys communis Matsumura that has been released in 2007 throughout the Midwestern USA as part of a classical biological control project against the invasive soybean aphid, Aphis glycines (Gahan). First, I designed a series of laboratory experiments to assess egg load and the risk of egg limitation in female B. communis in response to temperature, sugar feeding, and host availability. These experiments showed that B. communis maintains a constant egg load by varying its egg maturation rate in response to oviposition events. I hypothesized that such a rapid egg maturation might help minimize the risk of egg limitation under field conditions. Therefore, in the summers of 2007 and 2008 I conducted a release-and-recapture study to assess egg load and nutritional state of field-collected parasitoids and was able to show that the majority of female parasitoids maintained a relatively constant egg load under field conditions. In the summer of 2009, I designed a no-choice test that explicitly addressed host choice behavior in field-collected B. communis. Host specificity in B. communis was maintained in field-collected females, but low host availability and detrimental weather conditions increased the likelihood of females accepting the low-quality host species. In the summer of 2010, I designed a field study that assessed the host choice behavior in free-foraging B. communis. Overall, the results of both laboratory and field studies strongly suggested that B. communis maintained a high level of host specificity.