Differential impact of adults and nymphs of a generalist predator on an exotic invasive pest demonstrated by molecular gut-content analysis

Abstract

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.

Insect communities in soybeans of eastern South Dakota: The effects of vegetation management and pesticides on soybean aphids, bean leaf beetles, and their natural enemies

“…O. insidiosus and S. rubricaudus were consistently more abundant in the cover crop system than in the other two management systems (Table 1). O. insidiosus is an important predator of soybean thrips and the soybean aphid (Brosius et al, 2007;Butler and O'Neil, 2008;Desneux and O'Neil, 2008;Harwood et al, 2009). This omnivorous bug also has strong preferences for specific plant species as oviposition sites, and increased vegetation diversity has been shown to increase O. insidiosus populations (Lundgren et al, , 2009bSeagraves and Lundgren, 2010).…”

Biological Control, Functional Biodiversity and Ecosystem Services in Insect Pest Management

“…Harwood et al ( 2009 ) found mixed species diets were optimal, compared with restricted diets of pests alone on carabid Pterostichus melanarius Illiger and the linyphiid spider, Erigone atra Blackwall, with respect to life cycle parameters and predator survival. Many earlier reports corroborate this fact (Luck et al 2003 ) .…”

Feeding habits of lycosid spiders in field habitats

“…Under certain conditions, they have the potential to maintain pest populations below economic thresholds and thus provide an important ecosystem service to the agricultural sector acting as biological control agents (Chiverton 1986;Ö stman et al 2001. In addition to specific pests, generalist predators may consume alternative food items including other herbivores, decomposers such as earthworms and Collembola (Juen and Traugott 2007; King et al 2010;Kuusk and Ekbom 2010), Dipterans (Harwood et al 2007), and other natural enemies (Harwood et al 2009). By comparing rates of predation derived from molecular gut-content assays with the observed proportion of the target prey in the field, the hypothesis that generalist predators are capturing prey at random can be tested.…”