Ecological intensification that promotes arthropod biodiversity and increases ecosystem services is a challenge for future agriculture. And, realizing the full potential of arthropod biodiversity to promote sustainable pest management requires an understanding of predator-prey interactions and functional roles of generalist predators. However, little is known about the structure of food webs and dynamics of these feeding relationships in many agricultural systems throughout the world, and understanding food web behavior is critical to harvesting natural pest control services. In this study, we investigated the feeding relationships of common generalist arthropod predators and seven cotton pest species and alternative prey collected in a grid system of points separated by 50m. A total of three samples were collected each year (2015-2017) during key cotton developmental stages: vegetative growth, flowering, and boll development. We identified trophic links between the predator species, pest species and alternative prey with DNA-based molecular gut content analysis. Abiotic environments, the cotton terrain, for the sample locations included soil texture, percent slope, and elevation measured in the first year, and NDVI was measured at each cotton stage in each year. Community structure and trophic interactions (PCR positives for prey taxa) were analyzed using non-metric multidimensional scaling analysis and PERMANOVA to test for significant environmental predictors influencing predatory arthropod communities and predator-prey interactions.
Results/Conclusions
In 2015 and 2016, the dominant predators testing positive for prey and alternative prey were Salticidae spiders, Coccinellidae species and Geocoris spp. Major prey species detected were aphids, thrips and spidermites. In 2017, predator abundance was evenly distributed, and the major prey species detected were aphids and thrips spp. Communities and predator-prey interactions varied within season and between years. The most profound seasonal difference was in 2017, where there appeared to be no clear dominant predator species, but a strong dominance of predation on aphids. The disproportionate predation on aphids was surprising given that aphids were lower in population in 2017 as compared to prior years, and the populations of whiteflies were extremely high in 2017, reaching upwards of 1200 individuals on small sticky cards. Results, therefore, suggest that biocontrol is operating on some species that can be a problem (i.e. aphids, spider mites, and thrips), but predation levels on pests such as mid-late season stink bugs and late season whiteflies by the current naturalized predator communities are insufficient to control these pests.