The Effect of Neonicotinoids on Thrips Oviposition, Immatures, and Cotton Injury

Thrips are one of the major pests of seedling cotton (Gossypium hirsutum L.) in the U.S. Whereas previous studies have investigated the effects of neonicotinoids on reducing adult and immature thrips on cotton, their effect on oviposition in the field is understudied. In this study the effect of three neonicotinoid insecticide seed treatments on the number of thrips adults, immatures, eggs, plant injury, and plant biomass were evaluated. The experiment was replicated six times over weekly planting dates. Insecticides reduced thrips oviposition and immature thrips on seedlings. Seedlings from plantings in April had lower oviposition and number of immature thrips than seedlings planted in May, and the efficacy of insecticides against oviposition and immature thrips was reduced as seedlings reached four to five true leaves. Oviposition was not reduced by insecticides in seedlings planted after 2 May that were exposed to larger numbers of adult thrips. Insecticides reduced plant injury, which was variable across planting dates and growth stages. Differences in biomass were observed only on the last planting date and were likely due to more favorable growing conditions. The efficacy of these insecticide seed treatments to reduce thrips oviposition and numbers of immature insects depends upon pest population pressure, growth stage of the cotton, and growing conditions of the crop.