Identification of thrips species and resistance of Frankliniella occidentalis (Thysanoptera: Thripidae) to malathion, spinosad, and bifenthrin in blackberry crops

Mexico is among the most important blackberry producers in the world. In this crop, thrips damage is associated with poor fruit set. The objectives of this study were to identify the main thrips species associated with the flowers of cultivated blackberries, and to determine the resistance level of 13 field-collected populations of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), to the insecticides malathion, bifenthrin, and spinosad in the states of Michoacan and Jalisco, Mexico. Verification of F. occidental's was conducted by morphology and PCR amplification of the cytochrome oxidase I (COI) partial gene using LCO and HCO primers The susceptibility of adult thrips to insecticides was determined using residual contact exposure on bean (Phaseolus vulgaris L; Fabaceae) leaf sections dipped into aqueous solutions of 8 different concentrations of malathion, bifenthrin, and spinosad. The morphological identification of thrips from 8 different sampling zones confirmed that the main thrips species associated with blackberry flowers was F. occidentalis. However, Retanathrips funestus (Hood), Frankliniella insularis (Franklin), Frankliniella tolucensis Watson, Taenothrips frici (Uzel), and Isoneurothrips australis Bagnall (all Thysanoptera: Thripidae) also were found. Most of the evaluated populations of F. occidentals showed significant differences from the susceptible population in terms of the level of resistance to bifenthrin, malathion, and spinosad. The resistance ratios (RR50) for malathion varied from 36 to 2,458, followed by 4 to 974, and 2 to 248 in bifenthrin and spinosad, respectively. These results suggest the need to establish insecticide resistance management programs, particularly in zones that resulted in the highest levels of insecticide resistance.