Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2009
Publication Date: 2/14/2009
Citation: Desneux, N., Barta, R.J., Hoelmer, K.A., Hopper, K.R., Heimpel, G.E. 2009. Multifaceted determinants of host specificity in an aphid parasitoid. Oecologia. 160:387-398.
Interpretive Summary: The exotic Asian soybean aphid invaded North America in 2000 and has become a major pest of soybeans, causing substantial yield losses and resulting in costly pesticide applications. Foreign exploration in Asia identified a natural enemy of soybean aphid, the parasitic wasp Binodoxys communis, which was evaluated in laboratory studies to determine its specificity to soybean aphid as compared to other aphids. The specificity of insect natural enemies and herbivores is determined by behavioral and physiological factors governing host acceptance and suitability. Laboratory experiments identified several possible mechanisms of host specificity of this wasp when exposed to twenty species of aphids. In some hosts, wasp mortality occurred in the egg or early larval stages but for others it occurred in late larval stages. Possible causes for low suitability of certain aphid species include the presence of symbiotic bacteria that help aphids resist attack by wasps, and presence of toxins in some plants fed on by aphids. This research highlights the complex nature of host specificity in parasitoids.
Technical Abstract: The host specificity of insect parasitoids and herbivores is thought to be shaped by a suite of behavioral and physiological factors that mediate host acceptance and host suitability. We conducted laboratory experiments to identify mechanisms shaping the host specificity of the aphid parasitoid Binodoxys communis. Twenty species of aphids were exposed to B. communis females in microcosms, and detailed observations and rearing studies of 15 of these species were done to determine whether patterns of host use resulted from variation in behavioral factors such as host acceptance or variation in physiological host suitability. Six species of aphids exposed to B. communis showed no signs of parasitism. Four of these species were not recognized as hosts or and 2 effectively defended themselves from attack by B. communis. Other aphid species in which parasitoids laid eggs had low suitability as hosts. For some of these hosts, parasitoid mortality occurred in the egg or early larval stages but for others it occurred in late larval stages. Two hypotheses explaining low suitability were investigated in separate experiments: (i) the presence of endosymbiotic bacteria conferring resistance to parasitoids, and (ii) aphids feeding on toxic plants. An association between resistance and endosymbiont infection was found in one species (A. craccivora), and evidence for the toxic plant hypothesis was found for the milkweed aphids A. asclepiadis and A. nerii. This research highlights the multifaceted nature of factors determining host specificity in parasitoids.