Monitoring of Resistance in Field Populations of Scirtothrips dorsalis (Thysanoptera: Thripidae) and Diaphorina citri (Hemiptera: Liviidae) to Commonly Used Insecticides in Citrus in Central India.

Abstract

Field populations of thrips (Scirtothrips dorsalis Hood) from citrus nurseries and psyllids (Diaphorina citri Kuwayama) from commercial citrus orchards of three districts in Maharashtra State in India were evaluated for levels of resistance to organophosphates (acephate, chlorpyrifos, quinalphos, and dimethoate), neonicotinoids (thiamethoxam, imidacloprid), abamectin and spinosad between 2012 and 2017. Leaf dip bioassays for thrips and shoot tip bioassay for nymph and adult psyllids were used to assess levels of insecticide resistance as indicated by resistance ratios (RRs). In general, levels of insecticide resistance were zero (RR = 1) or very low (RR = 2-10); however, we recorded 21.0- and 28.0-fold increase in resistance (RR = 21-50) to spinosad 45SC in S. dorsalis between 2016 and 2017 that may be attributed to the continuous application of the insecticide for the management of various sucking insect pests of citrus. We found that levels of resistance to insecticides in adult and nymph D. citri collected from the three districts were zero to low (RR = 2-10). Our data show there may be a shift in resistance to neonicotinoid insecticides that are widely used among citrus growers in the study region. Results from this study indicate that the evolution of insecticide resistance and cross-resistance may be decelerated by the rotational use of insecticides with different modes of action.