The diamondback moth, Plutella xylostella is a cosmopolitan pest that has evolved resistance to all classes of insecticide, and costs the world economy an estimated US $4-5 billion annually. We analyse patterns of variation among 532 P. xylostella genomes, representing a worldwide sample of 114 populations. We find evidence that suggests South America is the geographical area of origin of this species, challenging earlier hypotheses of an Old-World origin. Our analysis indicates that Plutella xylostella has experienced three major expansions across the world, mainly facilitated by European colonization and global trade. We identify genomic signatures of selection in genes related to metabolic and signaling pathways that could be evidence of environmental adaptation. This evolutionary history of P. xylostella provides insights into transoceanic movements that have enabled it to become a worldwide pest.

BACKGROUND Empoasca onukii, the tea green leafhopper, is a key pest of tea whose control often requires the extensive use of insecticides. As a predator of the tea green leafhopper, the mite Anystis baccarum is a potential biological control agent worldwide, though little is known about how intercropping cover crops can impact its suppressing effect on E. onukii. Therefore, we conducted a field experiment to investigate how the relationship of the abundance of the predatory mite and its leafhopper prey is influenced by two different cover crops and a manually weeded inter‐row treatment as a contrast to naturally growing vegetation in a tea plantation in China. RESULTS The abundance of A. baccarum was significantly higher in tea canopies of intercropped treatments than in canopies over natural ground cover. Litter samples showed higher abundances of A. baccarum when tea was intercropped with Paspalum notatum than with natural ground cover in the first year of treatment. The abundance of E. onukii in tea canopies was higher over the bare ground treatment in the first year but the opposite was observed in the second year. CONCLUSIONS Results suggest that the abundance of A. baccarum in a tea plantation is influenced by intercropping and it can affect its leafhopper prey, albeit with varying levels of suppression. For informing biological control and suppression of pests, long‐term experiments are needed to investigate the interactions of both pest and predator with cover crop treatments. © 2019 Society of Chemical Industry

Tea is an economically important crop, consumed by billions of people. Despite the increasing market for pesticide-free products, the use of pesticide in tea is still high. In order to investigate whether intercropping promotes biological control organisms, Chamaecrista rotundifolia (Pers.) Greene, Indigofera hendecaphylla Jacq., Trifolium repens L., and Vigna sinensis (L.) were separately intercropped with free weeding as control in a tea plantation at Yangli, China. Arthropods were collected by taking sweep-net samples, and treatment effects on assemblages were investigated. The combined species richness of all arthropods and that of parasitoids was significantly increased in intercropped treatments while the species richness of herbivores and predators was only greater in C. rotundifolia and I. hendecaphylla intercropped treatments. Compared with control, the combined abundance of all arthropods, and that of herbivores was lower, while the abundance of parasitoids and its taxa was greater in all intercropped treatments. The abundance of predators and its taxa was greater only in tea plantations intercropped with C. rotundifolia or I. hendecaphylla. Of the herbivores, the abundance of Empoasca onukii Matsuda, Sternorrhyncha, Aleyrodidae, and Pentatomidae was greater in the areas intercropped with C. rotundifolia in comparison with the control, but the abundance of Thysanoptera and Geometridae caterpillars was lower. The recorded increase in the abundance of beneficial arthropods may explain the lower abundance of Thysanoptera or Geometridae caterpillars detected in the intercropped tea plantations. Our results indicate that intercropping has the potential to enhance arthropod biodiversity, and to provide an option for sustainable pest control in tea plantations.

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