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

Neonicotinoid insecticides such as imidacloprid (Admire Pro®) and thiamethoxam 
(CruiserMaxx®) are beginning to replace old-class broad-spectrum insecticides such as aldicarb (Temik®) and phorate (Thimet®). Neonicotinoids are preferred due to their 
efficacy against thrips, ease of application, and low costs. However, recently their 
efficacy has not been reliable. Reasons speculated included resistance development in thrips among others. In 2015, we assessed the efficacy of neonicotinoid insecticides 
against tobacco thrips by estimating their LCso values, and also how those values varied between lab and field populations. Resistance ratios were determined between field and laboratory populations. Results indicated no evidence for resistance against thrips in 
peanuts. The efficacy of insecticides in relation to application timing was also assessed using peanut leaf tissue residue analysis and bioassays with thrips. Peanut leaf tissue 
samples were periodically sampled following imidacloprid, thiamethoxam, and phorate treatments and sent for residue analysis. Also, bioassays were conducted with adult 
thrips and mortality percentages were determined. More experiments were conducted with the larvae to assess how insecticide applications could reduce larval feeding and 
suppress their development on treated peanut leaflets over time. This information is 
critical, as tobacco thrips (F. fusca) colonizes peanut leaflets effectively, and could also facilitate transmission of TSWV. More research is underway to examine efficacy issues including resistance to neonicotinoids in thrips in peanut.