Research Accomplishment Reports 2011

Effects of Prey Biodiversity on Pest Regulation by Generalist Predators

J.D. Harwood
Department of Entomology

 

Non-Technical Summary

Increased acreage of low-input, sustainable and organic agriculture can enhance biodiversity of predator and prey populations, with a concomitant reduction in pesticide application. However, the changing structure of arthropod populations may have profound effects on food web processes and ecosystem functioning. We have a very poor understanding of the consequence of these changes relative to integrated management of pests in agriculture; enhanced biodiversity can promote natural enemy population growth, but conversely may divert predators from feeding on target pests and towards alternative food sources. This research will therefore focus on identifying the structure of arthropod communities in agroecosystems, and the consequence of biodiversity on foraging dynamics of arthropod predators.

2011 Project Description

Current research in winter wheat is exploring ways that natural weed strips provide a conservation boundary to real-production wheat that can serve to mitigate the effects of virus transmission by aphids. The central premise to this work is that the provisioning of refugia surrounding crop fields enhances natural enemy populations that directly impact pest densities and thus reduce disease transmission. The integration of immunoassay, molecular and ecological experiments that utilize spatial models are being analyzed to examine the source/sink dynamics of predator and prey populations within these refugia.

Research in alfalfa continues to examine how niche partitioning among generalist predators enhances biological control through utilization of prey diversity at different strata within the crop. Additional research in corn agroecosystems continues to explore how prey diversity influences the feeding dynamics of generalist predators, with a particular focus on the role of non-prey (pollen, etc.) resources structure food webs.

Experimental surveys are underway in soybean agroecosystems that examine how spatial dynamics of crop and non-crop environments impact biodiversity of ants and the role of these predators in biological control. This project seeks to integrate GIS, molecular ecology, spatial ecology and behavior to tease apart the fine-scale interactions between predators and prey. This study also examines the role of extra-floral nectaries (and other non-prey resources) in influencing predator dynamics.

Twenty three research presentations were given at regional, national and international meetings by the PI, graduate students and postdoctoral scholars. Meetings where research was presented were as follows: Entomological Society of America Annual Meeting (Reno, NV), International Meeting on Understanding and Managing Ecological Novelty (Monte Verita, Switzerland), American Arachnological Society Annual Meeting (Portland, OR), Entomological Society of America North Central Branch Annual Meeting (Minneapolis, MN) and the Entomological Society of America Pacific Branch Meeting (Kona, HI). These included four invited symposium presentations.

Additionally, research was presented at the University of Kentucky Field Demonstration Day at UK-Research Education Center, Princeton, KY. This field demonstration documented ongoing research in winter wheat that seeks to understand the role of natural enemies in reducing disease transmission by aphid pests.

2011 Impact

This project seeks to quantify the structure and function of generalist predator food webs in agroecosystems. This is of fundamental importance when understanding biological control - characterization of food web interactions provides a sound framework for utilizing and enhancing predator populations that most effectively impact pest species.

Major "changes in knowledge" that result from this project are documented below.

(1) Use of generalist predators for management of invasive pests in strawberry agroecosystems. Diagnostic molecular gut-content analysis was used to examine the strength of trophic interactions between carabid beetles and slugs. Field collections revealed two major predators of slugs, Harpalus pennsylvanicus and Chlaenius tricolor, which revealed the potential importance of these natural enemies of slugs in the Nearctic.

(2) Phenological dynamics of predators in alfalfa. Agroecosystems are characterized by high disturbance that required rapid recolonization of the habitat for natural enemies to successfully impact pest populations. Large scale field research was integrated with time-series analysis to reveal phonological patterns of immigration by predators in relation to crop cycles in alfalfa. Crucially, the timing of peak immigration corresponded with the early phase of the pest population cycle, during which natural enemies have the maximum impact on pest populations. This suggests that these predators are capable of contributing to pest suppression as part of the assemblage of natural enemies and has the capacity to be integrated into future pest management decisions.

(3) Importance of non-pest prey for aphidophagous coccinellids. Non-prey food items have the capacity to sustain generalist natural enemies when pest populations are low. Thus they serve as a critical resource in biological control programs and their diversity can enhance the fitness and fecundity of predators. Using a Diptera-specific monoclonal antibody, research examined the importance of these non-pest prey to coccinellid larvae, themselves major predators of pest aphids. Significant numbers of predators screened positive for dipteran prey, suggesting that they provide a valuable (and previously undocumented) food resource in the field.

(4) Interaction of transgenic crops with spiders. Genetically engineered crops are an important part of the agricultural landscape. Therefore understanding the interaction between these crops, natural enemies and prey biodiversity is crucially important. In a major meta-analysis, spider families responded differently to Bt crops, and spider responses to insecticides are species- and toxin-specific, thus highlighting the need for greater taxonomic resolution in future research.

2011 Publications

Welch, K.D., Harwood, J.D. (2011). Predator-pathogen interactions: synergy between mortality causes and failure of the healthy herds hypothesis. Functional Ecology, 25, 943-944.

Eskelson, M.J., Chapman, E.G., Archbold, D.D., Obrycki, J.J., Harwood, J.D. (2011). Molecular identification of predation by carabid beetles on exotic and native slugs in a strawberry agroecosystem. Biological Control, 56, 245-253.

Moser, S.E., Kajita, Y., Harwood, J.D., Obrycki, J.J. (2011). Evidence for utilization of Diptera in the diet of field-collected coccinellid larvae from an antibody-based detection system. Biological Control, 58, 248-254.

Peterson, J.A., Lundgren, J.G., Harwood, J.D. (2011). Interactions of transgenic Bacillus thuringiensis crops with spiders (Araneae). Journal of Arachnology, 39, 1-21.

Welch, K.D., Crain, P.R., Harwood, J.D. (2011). Successional dynamics of web-building spiders in alfalfa: implications for biological control. Journal of Arachnology, 39, 244-249.