Detection of the invasive tomato red spider mite, Tetranychus evansi Baker & Pritchard (Acari: Prostigmata: Tetranychidae) in Australia based on morphological identification and DNA sequence analysis

Australia is an island nation and is free from many of the pests and disease found in other parts of the world. Therefore, Australia developed a national response mechanism to respond to detections of exotic pests. This mechanism includes early detection surveillance and identification services. Tomato red spider mite, Tetranychus evansi Baker & Pritchard is a serious pest of solanaceous plants (including tomato, potato and eggplant) in many parts of the world. T. evansi was first detected in Australia in August 2013 at Sydney, New South Wales. As part of a response to an exotic incursion, a delimiting survey was initiated. Other Tetranychus species exist in Australia and identification techniques were required to identify different species. Submitted survey samples were identified to species level using morphological keys and molecular sequence analysis of the mitochondrial cytochrome c oxidase I (COI) gene. Surveillance results of Solanaceae host plants at the time determined it was not technically feasible to eradicate this emergency plant pest (EPP). Additional to blackberry nightshade (Solanum nigrum L.), tomato, potato and sweetcorn, T. evansi was found damaging native kangaroo apple, Solanum aviculare G. Forst., (a new host plant record) and naturalised capeweed, Arctotheca calendula (L.) Levyns (Asteraceae). COI sequence analyses confirmed the morphological identifications of three different Tetranychus species (including T. lambi Pritchard & Baker and T. ludeni Zacher) among samples and further identified all twelve T. evansi specimens to a single mitochondrial haplotype (clade1; H4) previously reported from climatically diverse locations in Africa, East Asia and the Mediterranean region. Currently, T. evansi is considered to be an established plant pest in NSW, so far extensively recorded in the Sydney Basin. Based on the lack of COI sequence variation diversity among the Australian specimens of T. evansi, we suggest that this species was likely introduced from a single genetically depauperate source population. This genetic lineage of T. evansi established now in Australia was previously reported as invasive in semi-arid and cold regions outside of the species preferred distribution, and laboratory trials have indicated its propensity for increased tolerance of cold climate habitats. This has implications concerning potential for further spread of this lineage of T. evansi to a broader range of habitats and plant hosts in Australia.