Dominated Species and the Predation Assessment of Natural Enemies on Thrips in Cotton Fields in Xinjiang

Thrips is a major pest in cotton fields in Xinjiang. The objective of this study is to select their dominated predatory natural enemies and assess the predation efficiency on thrips, and to provide scientific insights for the development of biocontrol on thrips in cotton fields.

The population dynamics of thrips and their predators in Korla cotton field in southern Xinjiang were systematically investigated by visual inspection within five-point sampling in different blocks from 2021 to 2022. Predators’ samples were collected at different growth stages of cotton fields and detected by molecular detection, DNA of the whole natural enemy was extracted first, and PCR amplification was performed using the specific primers of Thrips tabaci and Frankliniella intonsa to obtain the species information of thrips in various natural enemies, then the quantitative food web of predator-thrips was constructed, and the differences of related food web structure at different growth stages of cotton were compared. In addition, basing on the predator-prey functional response model, the predation function of different predators (including adults and juveniles) on thrips was evaluated in laboratory by setting the prey density of 50, 100, 200, 300 and 400 individuals per Petri dish.

The population density of thrips was low at the seedling and budding stages but was high at the flowering-bolling stage. Annual population peaks occurred from late-July to early-August. Basing on the population dynamic, Hippodamia variegata is the dominated predator for thrips that occurred across the seeding, budding, flowering and bolling stages, while Campylomma diversicornis is the dominated predator in the late of flowering-bolling stage. The results of molecular detection showed the detection rate of thrips was high in the gut of H. variegata in the whole growth period of cotton, the detection rate of thrips in the gut of Coccinella undecimpunctata at seeding-budding stage was high, and the detection rate in the gut of C. diversicornis was also high at flowering-bolling stage. The predatory function response in laboratory indicated the predation ability of different predators on F. intonsa increased with the increase of prey density, the predation function of the larvae of H. variegata, the nymph of C. diversicornis and the larvae of Chrysoperla carnea was consisted with the Holling-Ⅱ model, whereas the predation function of the adult, such as H. variegata and C. diversicornis was suited with the Holling-Ⅲ model; when high prey density of 400 individuals thrips per Petri dish was provided, the consumed number of thrips for the adult of H. variegata was significantly higher than the larvae, the adult and nymph of C. diversicornis and the larvae of C. carnea.

H. variegata is the dominant predator for thrips across the whole cotton growth period, and C. diversicornis is the dominant predator in the late of flowering-bolling stage. This study provides a scientific insight for the utilization of predators to suppress thrips in cotton fields in Xinjiang.