Fecundity compensation by caged soybean aphid (Aphis glycines) populations does not prevent eventual suppression by the parasitoid Lysiphlebus orientalis

Monday, November 17, 2014: 9:00 AM
D133-134 (Oregon Convention Center)
Matthew C. Kaiser , Department of Ecology, Evolution and Behavior, University of Minnesota, Saint Paul, MN
George E. Heimpel , Department of Entomology, University of Minnesota, Saint Paul, MN
Resource species often respond to attacks by consumer species by either developing defenses or changing reproductive strategies (fecundity compensation). While fecundity compensation is probably best understood in plants, it has been documented in a number of animals as well. One such animal system includes soybean aphid (Aphis glycines) and the parasitic wasp Lysiphlebus orientalis. We have previously shown that offspring of parasitized aphids in this system reproduce at a greater rate than aphids whose mothers were not parasitized. Furthermore, this increase in fecundity is not associated with a tradeoff in offspring quality in the next generation of aphids. These traits, and preliminary studies suggesting that L. orientalis may be unable to suppress soybean aphid, led us to consider it to be poor control agent for the invasive soybean aphid. In this experiment, we evaluated the ability of low and high initial densities of L. orientalis to suppress soybean aphid populations in caged mesocosm laboratory conditions over season-long time periods. These populations were compared with control populations of aphids raised in identical conditions but without parasitoids. Aphids in all cages with parasitoids were driven to extinction in less than 14 weeks. However, there was a pronounced increase in suppression over time in cages starting with high densities of parasitoids, while aphid populations in cages with low initial parasitoid density mirrored control populations over the first several weeks. Comparisons with previous, shorter-term experiments will be made, and implications for biological control agent assessment will be discussed.