Identification of mutations associated with pyrethroid resistance in the voltage-gated sodium channel of the tomato leaf miner (Tuta absoluta)

The tomato leaf miner, Tuta absoluta (Lepidoptera) is a significant pest of tomatoes that has undergonea rapid expansion in its range during the past six years and is now present across Europe, North Africaand parts of Asia. One of the main means of controlling this pest is through the use of chemical insecticides.In the current study insecticide bioassays were used to determine the susceptibility of fiveT. absoluta strains established from field collections from Europe and Brazil to pyrethroids. High levels ofresistance to l cyhalothrin and tau fluvalinate were observed in all five strains tested. To investigatewhether pyrethroid resistance was mediated by mutation of the para-type sodium channel in T. absolutathe IIS4eIIS6 region of the para gene, which contains many of the mutation sites previously shown toconfer knock down (kdr)-type resistance to pyrethroids across a range of different arthropod species, wascloned and sequenced. This revealed that three kdr/super-kdr-type mutations (M918T, T929I andL1014F), were present at high frequencies within all five resistant strains at known resistance ‘hot-spots’.This is the first description of these mutations together in any insect population. High-throughput DNAbaseddiagnostic assays were developed and used to assess the prevalence of these mutations in 27 fieldstrains from 12 countries. Overall mutant allele frequencies were high (L1014F 0.98, M918T 0.35, T929I0.60) and remarkably no individual was observed that did not carry kdr in combination with eitherM918T or T929I. The presence of these mutations at high frequency in T. absoluta populations acrossmuch of its range suggests pyrethroids are likely to be ineffective for control and supports the idea thatthe rapid expansion of this species over the last six years may be in part mediated by the resistance ofthis pest to chemical insecticides.