Intraguild interference of spiders and ladybirds in a cotton field: Evidence from their active time and aphid control efficiency

Abstract

AbstractIn field crop systems, biocontrol efficiency supported by various predators is not always enhanced with occurring simultaneously but can be reduced by predator interference, i.e., competition between predator individuals over access to their prey. Such interference may be related to the active time of each predator. In this study, predator exclusion experiments were used to selectively exclude either one or both predators and to examine the impact of the two predator groups on the suppression of cotton aphid (Aphis gossypii Glover) populations in a cotton field. Main predator species included Propylaea japonica (Thunberg) and Harmonia axyridis Pallas in the ladybird group, and Lycosa spp. and Erigone spp in the spider group. A greater number of spiders was observed in the morning and evening, while ladybird densities did not vary during the day. Removing all predators led to an increase in aphid numbers compared to the other treatments where predators were present. Removing either spiders or ladybirds had similar impacts on aphid control. It is likely that spiders provide an equal level of aphid mortality as ladybirds. When both spiders and ladybirds were present, aphid abundance did not differ from those treatments where only one predator group was present. The presence of both predators did not lead to more aphid suppression, indicating that interference between these predators may have occurred in the cotton field. Although these two predators partly diverged in their activity rhythms, interference may still have occurred and could be common in cotton fields.