Aphids are major pests of cotton crops in the Xinjiang Uygur Autonomous Region in China, and parasitoids are considered as important natural enemies in regulating aphid populations. However, information on aphid parasitoids in the Xinjiang cotton fields is limited, which hinders the study of aphid-parasitoid interactions and the application of conservation biological control against cotton aphids. In this study, a 3-year survey was conducted in a large geographical range that included three primary cotton planting areas in southern and northern Xinjiang. The population dynamics and the parasitism levels of an assemblage of aphids in the cotton fields were investigated along with the composition of the parasitoid community associated with these aphids. Aphid parasitization varied significantly within both years and seasons, with parasitism levels ranging from 0 to 26%, indicating that there is less effective biological control of parasitoids on aphids under field conditions. Among the primary parasitoids described, Binodoxys communis (Gahan) constituted 95.19% of the parasitoid species, followed by Praon barbatum Mackauer (3.15%), Trioxys asiaticus Telenga (1.01%) and Lysiphlebus fabarum Marshall (0.65%). Significant differences were found in the composition of the primary parasitoid species between the cotton seedling period (June) and the flowering period (July-August), and two more primary aphid parasitoids were found in the seedling period. Twelve hyperparasitoid species belonging to six genera were found in our study, of which Pachyneuron aphidis (Bouché), Syrphophagus species and Dendrocerus laticeps (Hedicke) were the dominant species. The composition of the hyperparasitoid community also differed significantly between the seedling and the flowering periods. The description of this parasitoid community-associated assemblage of aphids in cotton fields will facilitate the study of aphid-parasitoid interactions and promote the development of effective cotton aphid management strategies in Xinjiang.

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.

Knowledge about the prey preference of polyphagous predators is important for determining their ability to suppress pest insects. Tetranychus truncatus (Tetranychidae), Tetranychus turkestani (Tetranychidae), and Thrips tabaci (Thripidae) often coexist in crops. Neoseiulus bicaudus (Wainstein) is a native predatory mite that was recently observed in the Xinjiang Uygur Autonomous Region of northwest China. The objective of this study was to assess the potential of N. bicaudus as a bio-control agent against the three pest species mentioned above. The results showed that N. bicaudus protonymphs, deutonymphs, and adults can be effective biological control agents for the three pest species. Neoseiulus bicaudus at all three developmental stages exhibited a Holling’s Type II (convex) functional response to the prey. Neoseiulus bicaudus exhibited no preference between T. truncatus adults and T. turkestani adults, irrespective of the prey ratio. In comparison, N. bicaudus clearly preferred first-instar T. tabaci larvae to T. turkestani adults. The results of this study suggest that N. bicaudus could help control T. truncatus, T. turkestani, and T. tabaci. Among these pests, N. bicaudus may be most effective for first-instar T. tabaci.

With the recent increase in planting of fruit trees in southern Xinjiang, the intercropping of fruit trees and cotton has been widely adopted. From 2014 to 2016, a large-scale study was conducted in Aksu, an important agricultural area in southern Xinjiang, to compare the abundance and species composition of spider mites in cotton fields under jujube-cotton, apple-cotton, and cotton monocrop systems. The abundance of spider mites in cotton fields under both intercropping systems was generally higher than in the cotton monocrop. The species composition of spider mites also differed greatly between cotton intercropped with apple or jujube compared to the cotton monocrop. The relative proportion of Tetranychus truncates Ehara (Acari: Tetranychidae) in the species complex generally increased while that of another spider mite, Tetranychus dunhuangensis Wang (Acari: Tetranychidae), decreased under fruit tree-cotton systems. More attention should be paid to the monitoring and management of spider mites, especially T. truncates in this important region of China.

The use of chemical pesticides particularly acaricides can reduce the control efficacy of natural enemies. The objectives of this study were 1) to evaluate the toxicity of three acaricides to the phytoseiid mite Neoseiulus bicaudus (Acari: Phytoseiidae) by spraying acaricides on N. bicaudus adult females and 2) to determine the effect of these acaricides on the functional response of different stages of N. bicaudus to the prey Tetranychus turkestani Ugarov & Nikolski (Acari: Tetranychidae). The results indicated that the survivability of N. bicaudus differed among the three acaricides tested. Pyridaben exhibited the highest toxicity to N. bicaudus not only because it caused higher mortality but also because it reduced the peak consumption for adults and increased the peak consumption for deutonymphs of N. bicaudus. The two other acaricides, azocyclotin and bifenazate, also slightly reduced the peak consumption, but not significantly, and the overall functional response was not different from control, untreated predatory mites. Bifenazate (143–4,300 mg a.i./liter) was relatively nontoxic to N. bicaudus (less than 10% mortality) but highly toxic to T. turkestani (more than 95% mortality). Accordingly, bifenazate is the most suitable for maintaining N. bicaudus in the field. Combining bifenazate and azocyclotin with N. bicaudus is a possible strategy for T. turkestani management.

Neoseiulus bicaudus (Wainstein) (Acari: Phytoseiidae) is a generalist predatory mite that consumes several pest species, including Tetranychus turkestani (Ugarov et Nikolskii) (Acari: Tetranychidae) in the Xinjiang Uygur Autonomous Region. The release numbers of predatory mites are based on the populations of target pests and their ability to control them. Populations of T. turkestani and T. truncatus Ehara (Acari: Tetranychidae) often coexist and damage many crops. To determine whether the presence of the non-target prey T. truncatus affects the ability of N. bicaudus to control the target prey T. turkestani. The study evaluated the predation rate and functional response of N. bicaudus to 4 stages of T. turkestani in the presence of T. truncatus. The consumption of T. turkestani by N. bicaudus gradually decreased as the proportion of T. truncatus increased. The functional response of N. bicaudus to T. turkestani was not changed when T. truncatus was presented, which was consistent with a type II response. The attack rate of N. bicaudus on the egg, larva, and nymph of T. turkestani was significantly decreased and the handling time of N. bicaudus on T. turkestani was significantly extended when T. truncatus was presented. The preference index showed that the preference of N. bicaudus for eggs and female adults of T. turkestani decreased with increasing density of T. turkestani in the same proportion as T. truncatus. The presence of T. truncatus can negatively affect the predation of T. turkestani by N. bicaudus. We suggest that the number of N. bicaudus released to control T. turkestani should be increased when T. truncatus coexist.