Intraguild Predation of Hippodamia variegata on Aphid Mummies in Cotton Field

SIMPLE SUMMARY: When there are multiple natural enemies in the same ecosystem, intraguild predation between natural enemies will affect the population dynamics of target organisms and the effectiveness of biological control. It is necessary to study this relationship in depth to enhance the function of biological control. Hippodamia variegata (Goeze) and parasitoids are two types of dominant natural enemies of the cotton aphid Aphis gossypii Glover in Xinjiang, China. Among them, the ladybeetle preys on common aphids as well as parasitoids. This study measured the feeding choices of H. variegata towards mummies with different densities of A. gossypii. Meanwhile, investigation and sampling in the cotton field were conducted from 2017 to 2019. The predation of H. variegata individuals on aphids and mummies was detected using diagnostic PCR. The results showed that H. variegata had no obvious feeding preference towards live aphids and mummies, and preferred denser prey. The molecular detection results show that A. gossypii was the main prey source and medium of consumption of parasitoids for the ladybeetle. H. variegata had strong trophic links to both parasitoids and aphids. The above information is crucial for evaluating the pest control ability of H. variegata more comprehensively and strengthening the strategies for the biological control of aphids. ABSTRACT: Intraguild predation among arthropod predators in agricultural ecosystems may have a negative impact on biological control. At present, there are few direct reports on trophic relationships among participants of predation in field groups. In this study, we measured the feeding choices of Hippodamia variegata (Goeze) towards mummies with different densities of Aphis gossypii Glover. The dynamics of the occurrence of mummies in the cotton field were investigated over 2017–2019. Singleplex PCR and multiplex PCR were used to detect the predation of 2090 H. variegata individuals on aphids and mummies in Xinjiang cotton field, which revealed the intraguild predation frequency between H. variegata and various parasitoids. There was no obvious feeding preference of H. variegata towards live aphids or mummies, which mainly depended on the relative density of prey. Among the four species of aphids detected in H. variegata, A. gossypii had a high detection rate and was the main prey source of the ladybeetle in the cotton filed. Mostly, ladybeetles consumed parasitoids through mummies, with 6.39% directly feeding on adult parasitoids. H. variegata had strong trophic links to both parasitoids and aphids. We established a food web of aphids–primary parasitoids–hyperparasitoids–H. variegata, which can be used to evaluate the pest control ability of H. variegata from a new perspective.