Spider Mites: Genetic Models to Inform Herbivore and Chelicerate Biology

Spider mites (Acari: Trombidiformes; Tetranychidae) are globally important herbivore pests of crops. They have also become powerful genetic models for understanding chelicerate biology and the evolution of xenobiotic (i.e., pesticide) resistance and host plant adaptation. The first spider mite genome, that of Tetranychus urticae, uncovered dramatic expansions of gene families and horizontally acquired genes that associate with this species' very broad host plant range. While in its infancy, comparative genomics with other Tetranychidae species with more restricted host plant ranges is already uncovering relationships between gene content and host plant breadth. Further, quantitative genetic methods adapted to spider mites' life history now enable the identification of loci underlying adaptive traits, and functional studies are possible with RNAi and a recent breakthrough in high-efficiency gene editing. This review combines a primer in spider mite biology and experimental tractability with recent genome-enabled findings to highlight the potential of spider mites to inform Acari and chelicerate biology, as well as mechanisms of genetic adaptation and evolution more broadly.