Identifying inter- and intra-guild feeding activity of an arthropod predator assemblage

Understanding predatorprey interactions of the arthropod community in any given ecosystem is essential in pinpointing the biological control services provided by natural enemies. Hence, four prey-specific polymerase chain reaction (PCR) assays were developed to analyse the gut contents of the cotton predator community. The four targeted prey included a herbivore/pest, omnivore/pest, omnivore/beneficial, and carnivore/beneficial. First, prey retention tests were conducted to determine how long a prey item of each target species could be detected in a predator after ingestion. The assays yielded highly variable inter-assay and intra-assay prey detection efficiencies. Then, a multifaceted field study was conducted to quantify the population dynamics of the cotton predator assemblage and to assess the frequencies of predation that each predator species exhibited on the targeted prey. In total, 1794 predators, representing 17 arthropod families, were collected over two seasons using both sweep net and whole plant sampling procedures. The predator gut assays showed that there was substantial inter-guild predation occurring on the herbivore/pest, Bemisia tabaci (Gennadius); moderate intra-guild predation on the omnivore/pest, Lygus spp. (Lygus lineolaris (Palisot de Beauvois), L. hesperus Knight, and L. elisus Van Duzee) and the omnivore/beneficial, Geocoris spp. (Geocoris punctipes (Say), and G. pallens Stal); and very little intra-guild predation on the carnivore/beneficial, Collops vittatus (Say). The gut assays also revealed that DNA of the targeted pests, B. tabaci and Lygus spp., were found more frequently in insect predators than spiders; whereas there were no significant differences in predation between the predatory insects and spiders for the beneficial insects, Geocoris spp. and C. vittatus. Finally, there was a significantly higher frequency of predation events recorded for B. tabaci, Lygus spp., and Geocoris spp. in the sweep net samples. This indicates that the method of collection might influence the interpretation of the gut assay results.