Differential impact of adults and nymphs of a generalist predator on an exotic invasive pest demonstrated by molecular gut-content analysis
Generalist predators have the capacity to regulate herbivore populations through a variety of mechanisms, but food webs are complex and defining the strength of trophic linkages can be difficult. Molecular gut-content analysis has revolutionized our understanding of these systems. Utilizing this technology, we examined the structure of a soybean food web, identified the potential for adult and immature Orius insidiosus (Hemiptera: Anthocoridae) to suppress Aphis glycines (Hemiptera: Aphididae), and tested the hypotheses that foraging behaviour would vary between life stages, but that both adults and immatures would exert significant predation pressure upon this invasive pest. We also identified the strength of trophic pathways with two additional food items: an alternative prey item, Neohydatothrips variabilis (Thysanoptera: Thripidae), and an intraguild predator, Harmonia axyridis (Coleoptera: Coccinellidae). A. glycines constituted a greater proportion of the diet of immature O. insidiosus, but N. variabilis DNA was found in greater frequency in adults. However, both life stages were important early-season predators of this invasive pest, a phenomenon predicted as having the greatest impact on herbivore population dynamics and establishment success. No adult O. insidiosus screened positive for H. axyridis DNA, but a low proportion (2.5%) of immature individuals contained DNA of this intraguild predator, thus indicating the existence of this trophic pathway, albeit a relatively minor one in the context of biological control. Interestingly, approximately two-thirds of predators contained no detectable prey and fewer than 3% contained more than one prey item, suggesting the possibility for food limitation in the field. This research implicates O. insidiosus as a valuable natural enemy for the suppression of early-season A. glycines populations.
KeywordsAphis glycines Food web ecology Immature generalist predators Molecular gut-content analysis Predator-prey interactions
J.D.H., H.J.S.Y. and M.H.G. are indebted to their co-author, Bob O’Neil, who passed away prior to preparation of this manuscript, for his support, encouragement and insights into this research initiative. All experiments comply with the current laws and regulations of the United States of America. J.D.H. is supported by the University of Kentucky Agricultural Experiment Station State Project KY008043. This work was supported, in part, by a grant from USDA/CSREES NRI (2003–03334) as well as through support of the Indiana Soybean Alliance, and the North Central Soybean Research Program. This paper is publication number 08-08-053 of the University of Kentucky Agricultural Experiment Station.
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