The ecology of plot size in cotton arthropod field studies

The Arizona cotton integrated pest management (IPM) plan has successfully reduced the number of sprays and conserved natural enemies through threshold-based use of effective and selective insecticides to control two key pests, Bemisia argentifolii and Lygus hesperus. As new insecticidal traits and insecticides are released, the effects of these technologies on natural enemies and other non-target organisms must be assessed to verify their compatibility to the Arizona IPM plan. These studies must realistically represent what happens to non-target organisms exposed to these technologies in commercial fields. Plot size is an important consideration as potential movement among plots or from outside sources can influence the interpretation of insecticides effects. Field studies were designed to investigate the effects of plot size on biocontrol function and population dynamics of the cotton arthropod community (27 taxa measured), which includes the key generalist predator taxa: Collops spp., Orius tristicolor, Geocoris spp., Misumenops celer, Drapetis nr. divergens and Chrysoperla carnea s.l.. Flupyradifurone use was compared with an untreated check and a positive control treated with acephate in two years of replicated field studies with three different plot sizes ranging from 0.01 to 0.06 ha. Species abundance and community diversity, as well as novel use of predator to prey ratios and sentinel prey as indicators of biological control in cotton, were analyzed to reveal effects of plot size. This work may help improve field studies and the regulatory community better interpret insecticide and other effects on non-target organisms in cotton and other systems.