Resistance Monitoring And Biochemical Mechanisms Of Chlorpyrifos Resistance In Apolygus Lucorum (Me Yer-D(U|")R)

Area-wide cultivation of Bt cotton for controlling the cotton bollworm has effectively reduced the frequency of insecticides applications on cotton production, which resulted in the previously controlled insect mirids gradually became major pests and spread to a range of other host crops. Currently, management of the mirids relies exclusively on chemical insecticides, continuous and dominant use of chemical sprays has facilitated resistance development in this pest. In this paper, Apolygus lucorum, one of the major mirids in China was investigated. The susceptibility base-lines of chlorpyrifos, alpha-cypermethrin, emamectin and fipronil to A. lucorum were established and the resistances of different geographic populations to these four insecticides were monitored. Furthermore, a chlorpyrifos-resistant A. lucorum strain was selected and its biochemical mechanisms of resistance were evaluated. These results will provide useful information for the integrated management of A. lucorum and other mirids.1. Toxicity of15insecticides to the susceptible SLF strain of A. lucorumToxicity of15insecticides to SLF, a susceptible strain of A. lucorum was measured in laboratory with both glass-vial and leaf-dip bioassays respectively. The toxicity of15pesticides to A. lucorum with the glass-vial bioassay was ranked as:fipronil>bifenthrin> chlorpyrifos>fenvalerate>carbosulfan>lambda-cyhalothrin>alpha-cypermethrin> thiamethoxam>acetamiprid>indoxacarb>imidacloprid>emamectin>diafenthiuron>chlorfen apyr>chlorantraniliprole. The toxicity of15pesticides to A. lucorum with the leaf-dip bioassay was ranked as:fipronil>bifenthrin>chlorpyrifos>alpha-cypermethrin>fenvalerate> lambda-cyhalothrin>imidacloprid>carbosulfan>indoxacarb>emamectin>acetamiprid>thiam ethoxam>chlorfenapyr>chlorantraniliprole>diafenthiuron. The susceptibility base-lines of chlorpyrifos, alpha-cypermethrin, emamectin and fipronil to A. lucorum were established based on t the glass-vial bioassay. 2. Monitoring of insecticide resistance in field populations of A. lucorumResistance to four pesticides (chlorpyrifos, alpha-cypermethrin, emamectin, fipronil) was determined by a glass-vial bioassay in11field populations of A. lucorum collected from six cotton-growing areas in the Yangtze and Yellow River Valley from2009to2011. The results demonstrated that most A. lucorum field populations were still susceptible to these four insecticides, but a few had developed moderate levels of resistance to one or two chemicals. The resistance ratios of the BZ population in2011and the YC populationin2010to chlorpyrifos were20.1-and12.6-fold respectively. The resistance ratios of the BZ in2011and the CHZ in2011to alpha-cypermethrin were24.6-and21.7-fold respectively. Resistance monitoring data from2009to2011indicated that the susceptibility to these four insecticides in field populations of A. lucorum was declining. Therefore the risk of field populations of A. lucorum developing higher resistance to chemicals should get enough attention.3. Metabolic enzyme activities in field populations of A. lucorumThe activities of esterase, glutathione S-transferase and monooxygenases in nine A. lucorum populations from different areas were measured and the correlation analyses for bivariates between resistance folds of insecticides and enzyme activities were calculated. The results showed that three metabolic enzyme activities of the field populations were higher than that of the susceptible strain, but the increased metabolic enzyme activities were not correlated with insecticides resistance levels except that esterase activities were related with chlorpyrifos and fipronil resistance. The relationship between resistance levels and metabolic enzyme activities in field populations of A. lucorum should be further studied with more samples.4. Biochemical mechanisms of chlorpyrifos resistance in A. lucorumAn A. lucorum strain (BZCR) was selected from a field-derived population (BZ) with chlorpyrifos for4generations. The resistance factor to chlorpyrifos in BZCR was42.3-fold compared with the susceptible SLF strain. The activities of esterase, glutathione S-transferase and monooxygenases of BZCR were significantly higher than that of the susceptible SLF and the unselected BZ strains. Furthermore, the chlorpyrifos-resistance in BZCR was suppressed by the carboxylesterase inhibitor S,S,S,-tributylphosphorotrithioate, the cytochrome P450inhibitor piperonyl butoxide, and the glutathione S-tranferase inhibitor diethyl maleate, with synergism factors of5.2-,3.0-, and4.1-fold respectively. These results indicated that the increased detoxification may be associated with resistance to chlorpyrifos in the BZCR strain of A. lucorum.