Inheritance, Cross Resistance And Mechanisms Of Abamectin Resistance In A Field Population Of Plutella Xylostella

Plutella xylostella (diamondback moth, DBM) is one of the most destructive pests of cruciferous vegetables. DBM has evolved resistance to various kinds of insecticide in the field, and it also becomes one of the most difficult pests to control in the world. The avermectins are a group of fermentation products from a soil actinomycete Streptomyces avermitilis Kim & Goodfellow. They are 16-membered macrocyclic lactones with potent nematicidal, acaricidal and insecticidal activities. The abamectin has high potency against DBM. However, with intensively using, the field-evolved resistance to abamectin in DBM has become more and more serious. In this study, inherintance mode, cross resistance spectrum and resistance mechanisms of abamectin resistance were investigated in a field-derived strain of P. xylostella in order to provide essential scientific basis for designing resistance management strategies such as insecticide roations.1. Selection of abamectin resistance and cross-resistance patterns of abamectin resistance in the TH-Abm strainThe TH-Abm strain was selected with abamectin form TH strain, which was collected from Tonghai, Yunnan Province of China. After 30 generations of selection, resistance in the selected TH-Abm strain reached around 10,000-fold at F14 compared to a susceptible strain (Roth). Compared with the TH strain, the TH-Abm strain showed high levels of cross resistance to emamectin benzoate (950-fold), low levels of cross resistance to spinosad (10-fold) and fipronil (10-fold).2. Inheritance of abamectin resistance in the TH-Abm strainThe inheritance mode of resistance to abamectin was evaluated by using the methods of reciprocal crosses and backcross between the susceptible strain Roth and abamectin-resistant strain TH-Abm. The toxicities of abamectin to F1 progeny from reciprocal crosses between the TH-Abm and Roth strains were not statistically different from each other. This indicates that the abamectin resistance is autosomal. The degree of dominance (D) of resistance was calculated to be 0.38 and 0.40 at LC50, suggesting that abamectin resistance was incompletely dominant. In the log dosage-probit mortality curve of the backcross progeny to abamectin there was no distinct plateau corresponding to 50% mortality. Theχ2 test of the goodness of fit between the observations and predictions under the assumption of monofactorial inheritance rejects the single gene hypothesis. It suggests that abamectin resistance in the TH-Abm strain was controlled by more than one factors.3. Biochemical characterization of abamectin resistacne in the TH-Abm strainThe biochemical mechanisms of abamectin resistance in TH-Abm were studied by synergism tests and detoxifying enzyme activity tests. The results showed that PBO had 7.5- fold synergism to abamectin in TH-Abm strain, but neither the glutathione depleter DEM nor the esterase inhibitor DEF showed appreciable synergism in this resistant strain. P450 monooxygenase ECOD activity in strain TH-Abm was elevated 5.8- and 3.4-fold compared with the Roth and TH strains respectively. P450 monooxygenase MROD activity in strain TH-Abm was elevated 4.7- and 4.4-fold compared with the Roth and TH strains respectively. However, there was no significant difference in P450 monooxyenase PNOD activities between the three strains. Esterase activity and glutathione S-transferase activitiy towards were no significantly different between strains. The results implied that monooxygenase plays an important role in abamectin resistance in the TH-Abm strain.4. Cloning and sequence analysis of glutamate-gated chloride channel receptor genes from Plutella xylostellaA full-length cDNA of glutamate-gated chloride channel receptor alpha-subunit was cloned from Plutella xylostella by using PCT and RACE technique. Sequence analysis showed that this gene was 2071bp with an opened reading frame(ORF) of 1341 bp which encoded 447 amino acid residues. The comparasion of GluClαsequences between TH-Abm strain and TH strain showed that there were 10 different amino acids. These findings provide important basis for further study on mechanism of target resistance to abamectin in P.xylostella. KEY WORDS:Plutella xylostella; Abamectin; Resistance mechanism; Cross-resistance; Resistance inheritance;...