A rapid field-based assay using recombinase polymerase amplification for identification of Thrips palmi, a vector of tospoviruses.

Thrips palmi (Thysanoptera: Thripidae) is an important pest of vegetables, ornamentals, and legumes worldwide. Besides damage caused by feeding, it transmits several tospoviruses. Identification of T. palmi at an early stage is crucial in implementing appropriate pest management strategies. Morpho-taxonomic identification of T. palmi based on the adult stage is time-consuming and needs taxonomic expertise. Here, we report a rapid, on-site, field-based assay for identification of T. palmi based on recombinase polymerase amplification (RPA), its first application in insects. RPA primers designed based on 3' polymorphisms of the Internal Transcribed Spacer 2 region efficiently discriminated T. palmi without any cross-reactivity to other predominant thrips species. RPA was performed with crude DNA, extracted from single T. palmi simply by crushing in sterile distilled water and could be completed within 20 min by holding the reaction tubes in the hand. The assay was further simplified by using fluorescent as well as colorimetric dyes thus eliminating the gel-electrophoresis steps. The presence of T. palmi was visualized by a change in color from dark blue to sky blue. The assay was validated with known thrips specimens and found to be effective in diagnosing the presence of T. palmi in natural vegetation. This on-site, rapid assay for diagnosis of T. palmi can be used by non-expert personnel in the field of quarantine and pest management.