Incidence and molecular mechanisms of insecticide resistance in Frankliniella occidentalis, Thrips tabaci and other economically important thrips species

Thrips species (Thysanoptera) damage plants by direct feeding and transmitting plant viruses and are considered one of the most harmful insect pests on crops worldwide. Their control mainly relies on the use of insecticides, but due to their frequent use and several biological aspects of thrips, insecticide resistance has arisen. However, despite its economic impact, the molecular mechanisms of thrips resistance have been poorly investigated. Resistance mutations in genes encoding the target-sites of insecticides have been infrequently reported for only five target-site genes. As an illustration of the lack of knowledge, analysis of publicly available sequencing data revealed the presence of acetylcholine esterase resistance mutations A201S and F290V, which had not yet been reported from the field. Next, we also summarize the importance of metabolic resistance, historically inferred mainly from data from enzyme activity assays and synergism studies. As these only suggest main routes of detoxification without providing details on underlying genetic mechanisms, the rapidly changing availability of genomic data provides an impetus to dissect causal genes. As not all main detoxification families were annotated in the main species, we took advantage of recently published thrips genomes to annotate and compare the glutathione-S-transferase (GST) family of Frankliniella occidentalis and found a relatively higher number of sigma GSTs. A broader understanding of the molecular mechanisms of resistance and especially the identification of resistance mutations and key detoxification enzyme genes will drive the development of molecular diagnostic tools that can be used for monitoring insecticide resistance in thrips.