Examining issues associated with the efficacy of two neonicotinoid insecticides (CruiserMaxx and Admire Pro) against thrips on peanut in comparison with Thimet.

Recent increases in spotted wilt incidence is strongly correlated to increase in thrips populations and feeding injuries that accompany thrips infestations in early stages of peanut seedling growth. The shift from using broad spectrum insecticides such as aldicarb (Temik) and phorate (Thimet) to neonicotinoid insecticides such as imidacloprid and thiamethoxam could have influenced this outcome. lmidacloprid is being used in place of phorate more frequently. There has been an 
increased concern of resistance development towards neonicotinoids by thrips (tobcco thrips, 
Frankliniella fusca ). This prompted us to examine various aspects of imidacloprid effects on 
thrips, including assessing plant residue levels and associated thrips mortality, thrips 
susceptibility to imidacloprid in the lab and in the field, developing an imidacloprid-resistant 
thrips population, and identifying the molecular factors that determine resistance to 
neonicotinoids in thrips using transcriptomic and genomic approaches. Preliminary results 
indicate that the thrips susceptibility to imidacloprid seems to be more closely correlated to 
residue levels of the insecticide in the plant, as opposed to resistance to imidacloprid. Field 
sample testing for the last three years have indicated that the thrips are still susceptible to 
imidacloprid at pretty much the same level as that of the lab population. Numerous rigorous 
attempts to develop a resistant population by challenging our lab population with sub-lethal 
levels of imidacloprid has not yielded a stable resistant population yet, and efforts are underway to develop one such population. In addition, molecular factors such as detoxifying (pesticide) 
enzymes that influence susceptibility to imidacloprid and others have been identified and 
phylogenetically compared to other insects. However, the issues have been to narrow down the putative gene homologs. Numerous homologs have been identified for each target, and the fact that these homologs belong to multigene families has further complicated the issue. A more 
stringent approach would be to develop a genome for thrips to narrow down the targets. The 
plan is to undertake a genome development approach in the next one to two years.