No influence on population dynamics of spider mites in cotton fields of intercropping with walnut, a poor-quality host

Abstract

Intercropping is a common agricultural practice used to improve crop yields and profits; however, the intercrop species and its quality as a host for the main crop's key pests can affect the pests' population dynamics under intercropping conditions. Fruit trees - cotton intercropping systems are commonly applied in Xinjiang of China, and previous studies have confirmed that intercropping of cotton with species (e.g., jujube and apple) that are good spider mite hosts can increase the spider mite density in cotton. In this study, the effect of intercropping cotton with walnut, which is a poor host for the key spider mite pest Tetranychus truncatus, was examined. For this spider mite, feeding on walnut leads to significantly longer development time for larvae + nymphs and a short oviposition period which leads to a lower total fecundity, lower survival rate and lower intrinsic growth rate (rm) compared to cotton. Correspondingly, in the two-year, multiple-scale field study, we found that the population dynamics of spider mites in cotton did not significantly differ in the field plots between a walnut-cotton intercropping system and monocultural cotton. Similar trends of spider mite density were also observed in commercial fields. Based on previous work and the current study on fruit tree-cotton intercropping systems, we concluded that while intercropping cotton with intercrop species that are suitable spider mite hosts increase the spider mite population in intercropped cotton, the use of a poor host plant such as walnut has no significant effect on spider mites populations in cotton. Hence, our study results improved the understanding of pest management and monitoring in intercropped cotton systems.