The soybean aphid, Aphis glycines (Hemiptera: Aphididae), is a pest of soybeans in Asia, and in recent years has caused extensive damage to soybeans in North America. Within these agroecosystems, generalist predators form an important component of the assemblage of natural enemies, and can exert significant pressure on prey populations. These food webs are complex and molecular gut-content analyses offer nondisruptive approaches for examining trophic linkages in the field. We describe the development of a molecular detection system to examine the feeding behaviour of Orius insidiosus (Hemiptera: Anthocoridae) upon soybean aphids, an alternative prey item, Neohydatothrips variabilis (Thysanoptera: Thripidae), and an intraguild prey species, Harmonia axyridis (Coleoptera: Coccinellidae). Specific primer pairs were designed to target prey and were used to examine key trophic connections within this soybean food web. In total, 32% of O. insidiosus were found to have preyed upon A. glycines, but disproportionately high consumption occurred early in the season, when aphid densities were low. The intensity of early season predation indicates that O. insidiosus are important biological control agents of A. glycines, although data suggest that N. variabilis constitute a significant proportion of the diet of these generalist predators. No Orius were found to contain DNA of H. axyridis, suggesting intraguild predation upon these important late-season predators during 2005 was low. In their entirety, these results implicate O. insidiosus as a valuable natural enemy of A. glycines in this soybean agroecosystem.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. We investigate the potential effects of parasitoid egg limitation on host-parasitoid population dynamics. We define a parasitoid as egg-limited if a shortage of eggs means that at some time she cannot utilize an opportunity to oviposit. 2. We develop models which consider the differing physiologies of pro-ovigenic and synovigenic parasitoids to investigate the potential consequences of egg limitation. Pro-ovigenic parasitoids emerge with their full complement of mature eggs. Synovigenic parasitoids also emerge with some eggs, but can mature more later in life. 3. The models indicate that egg limitation in pro-ovigenic parasitoids has no effect on stability. This result is independent of the egg load distribution in newly emerged parasitoids, and of the maximum number of eggs with which a female emerges. In synovigenic models, however, egg limitation is found to be destabilizing, though the reduction in stability is decreased by (i) an increase in egg load at emergence, and (ii) a decrease in the 'latent' time required for egg maturation and gut emptying following a host meal. The latent period, during which time the full gut precludes feeding on hosts, differs from a conventional handling time in that host attacks (via oviposition) are still possible if the female has mature eggs. The maximum ovary storage capacity of females in a synovigenic parasitoid population has no effect on stability.

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