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Effects of Prey Biodiversity on Pest Regulation by Generalist Predators
Department of Entomology
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.
2009 Project Description
Ongoing field research throughout Kentucky is seeking to identify the role of generalist predators in biological control of crop pests, paying particular attention to the role of prey biodiversity on predation dynamics. As such, direct output to growers, extension agents, etc., can be obtained from this research as we seek to address pertinent questions to agriculture in the state. These experiments are currently being conducted in alfalfa, corn and winter wheat and include graduate student and postdoctoral scientist training in the agricultural sciences.
Mechanisms of foraging by generalist predators are being examined with a view to identifying their role in biological control. This is being achieved through the integration of molecular techniques, behavioral studies in the laboratory and field experiments. These approaches are being used in parallel to delineate trophic connectivity and measure the intensity of specific predator-prey interactions. Understanding the forces that regulate the abundance of these important natural enemies can ultimately provide information that discerns the role of prey biodiversity and habitat management on predation dynamics. Specific impacts are given in the Outcomes/Impacts section.
(1). Identification of trophic pathways in generalist predator food webs. Utilizing molecular gut-content analysis, the structure of a soybean food web was examined and the potential for adult and immature Orius insidiosus (Hemiptera: Anthocoridae) to suppress Aphis glycines (Hemiptera: Aphididae) assessed. 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) was identified. 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.
(2). Role of Coccinellidae in aphid biological control. Coccinellids and aphids interact in a wide range of agricultural and forest habitats and the value of coccinellid predation for aphid suppression in these systems varies from a minor role to significant reductions leading to within-season control. In a major review, a comparative discussion of the management of the cotton aphid (Aphis gossypii Glover) and the soybean aphid (Aphis glycines Matsumura) highlighted the importance of documenting levels of pest mortality by coccinellids.
(3). Effect of biodiversity of biological control. Experiments showed that a diverse diet significantly enhanced predator fecundity and survival. Experiments were conducted using common generalist predators found in arable fields in Europe, the carabid beetle Pterostichus melanarius (Coleoptera: Carabidae) and the linyphiid spider Erigone atra (Araneae: Linyphiidae). In conclusion, predators offered only pests (slugs or aphids) had lowest growth rates and fecundity and diversity significantly increased such parameters.
(4). Biological control of coffee berry borer. The coffee berry borer, Hypothenemus hampei (Coleoptera: Curculionidae), is the most important pest of coffee worldwide, causing an estimated $500 million in damage annually. H. hampei-specific primers were designed to demonstrate that H. hampei DNA can be detected in DNA extractions of a predatory thrips species, Karnyothrips flavipes, which preys on H. hampei. The potential of this molecular technique was demonstrated as being viable for unraveling the trophic interactions that occur inside the coffee berry.
Harwood, J.D., Yoo, H.J.S., Greenstone, M.H., Rowley, D.L. & ONeil, R.J. (2009). Differential impact of adults and nymphs of a generalist predator on an exotic invasive pest demonstrated by molecular gut-content analysis. Biological Invasions, 11, 895-903.
Obrycki, J.J., Harwood, J.D., Kring, T.J., ONeil, R.J. (2009). Aphidophagy by Coccinellidae: application of biological control in agroecosystems. Biological Control, 51, 244-254.
Thomas, R.S., Harwood, J.D., Glen, D.M., Symondson, W.O.C. (2009). Tracking subterranean density-dependent predation by carabid larvae on slugs using monoclonal antibodies. Ecological Entomology, 34, 569-579.
Harwood, J.D., Phillips, S.W., Lello, J., Sunderland, K.D., Glen, D.M., Bruford, M.W., Harper, G.L., Symondson, W.O.C. (2009). Reduced invertebrate biodiversity affects predator fitness and hence ability to control crop pests. Biological Control, 51, 499-506.
Chapman, E.G., Jaramillo, J., Vega, F.E., Harwood, J.D. (2009). Biological control of coffee berry borer: the role of DNA-based gut-content analysis in assessment of predation. In: 3rd International Symposium on Biological Control of Arthropods (Eds. Mason, P.G., Gillespie, D.R. & Vincent, C.). USDA-FHTET, Morgantown, WV, pp. 475-484.