Insecticide resistance in field populations of Asian citrus psyllid in Florida

Abstract

Asian citrus psyllid (ACP), Diaphorina citri, is a major pest of citrus because it vectors the putative causal agent of huanglongbing disease. Insecticides are currently the basis of psyllid management programs, and the number of annual insecticide applications has increased significantly. In this paper, a series of investigations of insecticide resistance among field populations of adult and immature ACP in Florida is described. In 2009, the highest level of resistance for adult ACP, as compared with the laboratory susceptible (LS) population, was found with imidacloprid with an LD(50) resistance ratio (RR(50) ) of 35 in one population. This was followed by chlorpyriphos (RR(50) = 17.9, 13.3, 11.8 and 6.9), thiamethoxam (RR(50) = 15 and 13), malathion (RR(50) = 5.4 and 5.0) and fenpropathrin (RR(50) = 4.8). In 2010, mortality of adults from all five sites sampled was lower than with the LS population at three diagnostic concentrations of each insecticide tested. Among nymph populations, indications of resistance were observed with carbaryl (RR(50) = 2.9), chlorpyriphos (RR(50) = 3.2), imidacloprid (RR(50) = 2.3 and 3.9) and spinetoram (RR(50) = 4.8 and 5.9). General esterase, glutathione S-transferase and monooxygenase levels were also elevated in field-collected adult and nymph ACP as compared with the LS population. The present results suggest that varying levels of insecticide susceptibility exist in ACP populations across the citrus-growing areas of Florida. Increased levels of detoxifying enzymes in these populations may partially explain these differences. The present results indicate that insecticide resistance may become an emerging problem for ACP control if effective resistance management is not practiced.