Analysis of the Predator Community of a Subterranean Herbivorous Insect Based on Polymerase Chain Reaction

Authors: Lundgren, Jonathan; Ellsbury, Michael; Prischmann, Deirdre

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2009
Publication Date: 12/1/2009
Citation: Lundgren, J.G., Ellsbury, M.M., Prischmann, D.A. 2009. Analysis of the Predator Community of a Subterranean Herbivorous Insect Based on Polymerase Chain Reaction. Ecological Applications. 19(8):2157-2166.

Interpretive Summary: The western corn rootworm (Diabrotica virgifera virgifera) is arguably one of the worst pests of agriculture worldwide, yet the predator community associated with it has largely been unexplored. We developed a new genetic technique (quantitative PCR, or qPCR) that amplifies rootworm-specific DNA sequences with predator guts. Also, a novel rotating pitfall trap was developed that allows us to study the activity patterns of predators over a 24 h period. With these tools, we described the predator community and ranked individual taxa based on the frequency of predation and the amount of prey DNA in their stomachs. First, the egg and larval stages of the rootworm were exposed to very different predator communities, and for the most part these predator taxa were easily grouped as day and night-active species. These are important developments in that they give insight into how these very abundant and diverse communities can partition themselves to reduce direct competitive interactions. The gut analyses revealed that harvestmen and rove beetles were the most frequent predators of rootworm immatures, but carabid beetles, predaceous mites, wolf spiders and other spiders were also playing a role in rootworm reductions. Two carabids and a wolf spider showed the highest degree of reliance on rootworms as prey. Finally, our study showed that sucking predators were better adapted as predators of rootworms than chewing predators, particularly during the rootworm larval stage. This research sets the groundwork for more directed studies on the development of biological control of western corn rootworm.

Technical Abstract: Using quantitative PCR and a novel pitfall trap design, we described the diel and seasonal activity patterns of the predator community in association with Diabrotica virgifera virgifera (WCR), generated a relative consumption index of WCR for the major predator operational taxonomic units (OTU), and determined relative consumption levels during the egg and larval stages of WCR by predator feeding guilds. Three cornfields were infested with WCR eggs, and temperature-based models were used to predict the occurrences and durations of the egg stage and each larval stadium. Adult emergence cages were used to validate the temperature models and determine the preimaginal mortality rates. A set of rotating pitfall traps that isolated captures into 3-hr intervals over a diel cycle was placed in the center of each plot, and predators were collected daily. WCR-specific PCR primers were developed and the guts of >1,500 predators were analyzed for the presence and quantity of target DNA. The egg stage of WCR persisted for a longer duration and incurred higher consumption intensity than the larval stage, and the egg and larval stages were subjected to unique predator communities. Predators formed distinct night- and day-active guilds, although WCR consumption was consistent throughout the diel cycle. More than 17 OTUs preyed upon WCR in the field, with the highest consumption levels being observed in phalangiids and small staphylinids (< 5 mm). Scarites spp. (Carabidae), Poecilus chalcites (Carabidae) and a lycosid species had the highest degree of reliance on WCR as prey. Predators with sucking mouthparts had a higher consumption level than chewing predators, particularly during the WCR larval stage. Thus a diverse community of predators attacks WCR in cornfields, and several ways that this community has partitioned their activity to exploit a limited set of resources are identified, and qPCR advances our understanding of the predator-prey interactions beyond traditional PCR.