Title: Inheritance and stability of mevinphos-resistance in Plutella xylostella (L.), with special reference to mutations of acetylcholinesterase 1 Lin CL, Yeh SC, Feng HT, Dai SM Ref: Pestic Biochem Physiol, 141:65, 2017 : PubMed
Diamondback moth (Plutella xylostella L.) causes enormous damage on cruciferous vegetables and can rapidly develop resistance to all kinds of insecticides. To effectively manage the insecticide resistance of P. xylostella, an understanding of its inheritance and stability is essential. Here we investigated the phenotypic and genotypic basis of mevinphos resistance by crossing two genetically pure lines of P. xylostella, an SHggt wild-type strain and an SHMTCN resistant strain carrying 892T/T, 971C/C, and 1156T/G (TCN) mutations of the acetylcholinesterase 1 gene (Pxace1). Similar median lethal concentrations and degrees of dominance in the reciprocal cross progeny, and no plateau on the log concentration-probit line of F1 backcross and self-cross progeny, suggest that the mevinphos-resistance in P. xylostella is inherited as an autosomal and incomplete dominant trait governed by more than one gene. In the absence of mevinphos exposure, the resistance ratio and Pxace1 mutation frequency declined concomitantly in the SHMTCN strain. After 20-generation relaxation, the mevinphos resistance decreased from 52- to 6-fold and the Pxace1 mutation frequency of the TCN haplotype pair decreased from 100% to 0%. A good correlation was found between the resistance ratio and TCN frequency within the range of 12.5- to 25-fold resistance. Since there was no TCN haplotype pair detected below a resistance level of 12.5-fold, we speculate that resistance mechanisms other than target site insensitivity may exist. These observations are important for the prediction and management of mevinphos and related organophosphate resistance in field populations of P. xylostella.
Title: Distinct contributions of A314S and novel R667Q substitutions of acetylcholinesterase 1 to carbofuran resistance of Chilo suppressalis Walker Dai SM, Chang C, Huang XY Ref: Pest Manag Sci, 72:1421, 2016 : PubMed
BACKGROUND: In the striped stem borer, Chilo suppressalis, A314S, R667Q and H669P substitutions in acetylcholinesterase 1 (CsAChE1) have been associated with >1000-fold resistance against carbofuran. In this study, eight variants of CsAChE1 carrying different combinations of these substitutions were cloned and expressed using the Bac-to-Bac expression system to verify their contributions. RESULTS: The expressed AChE1s had molecular weights of ca 160 kDa per dimer and 80 kDa per monomer. AChE kinetics and inhibition analysis showed that the A314S mutation was the key substitution responsible for a 15.1-fold decrease in hydrolytic activity to acetylthiocholine iodide and a 10.6-fold increase in carbofuran insensitivity of CsAChE. Compared with wild-type CsAChE1, this substituted CsAChE1 also showed 23.0-, 3.3- and 2.6-fold insensitivity to methomyl, triazophos and chlorpyrifos-oxon respectively. It should be noted that the R667Q substitution conferred a capability to increase the activity of wild-type and A314S-substituted CsAChE, while the A314S substitution reduced Km and compensated for overall catalytic efficiency. CONCLUSION: With the enhancing activity of the R667Q substitution, A314S is the major CsAChE1 substitution responsible for fitness-cost compensation and increased insensitivity to AChE inhibitors. The lower insensitivity of A314S-substituted CsAChE1 to chlorpyrifos-oxon suggests that chlorpyrifos could be an alternative insecticide for managing carbofuran-resistant field C. suppressalis in Taiwan. (c) 2015 Society of Chemical Industry.
Title: Amino acid substitutions of acetylcholinesterase associated with carbofuran resistance in Chilo suppressalis Chang C, Cheng X, Huang XY, Dai SM Ref: Pest Manag Sci, 70:1930, 2014 : PubMed
BACKGROUND: Over 1000-fold carbofuran resistance has been observed in Chilo suppressalis (Walker) collected from the Changhua (CH) and Chiayi (CY) prefectures of Taiwan. An understanding of the pertinent mechanisms will benefit effective insecticide resistance management of C. suppressalis. RESULTS: Among the five amino acid substitutions of acetylcholinesterase (AChE) identified in C. suppressalis, A314S and H668P had been reported and E101D, F402V and R667Q were novel. Substitution frequencies in AChE of CH and CY populations were much higher than in the susceptible Hsinchu (HC) population. Significantly negative correlations were observed between the frequencies of E101D, A314S and R667Q and the kinetic parameters of AChEs in these populations. AChE from the resistant CH population was less susceptible to the inhibition of carbofuran, with an I50 that was 3.6-fold higher than that of the susceptible HC population. Although Km and Vmax of AChE from the CH and CY populations were reduced to 72-87% of those from the HC population, the overall catalytic efficiency (Vmax /Km ) remained constant for all three populations. CONCLUSION: Amino acid substitutions identified in the AChE of C. suppressalis are associated with changes in AChE kinetics and its insensitivity to carbofuran. These observations are helpful for rapid monitoring, prediction and management of OP and CB resistance in the field. (c) 2014 Society of Chemical Industry.
Title: Amino acid substitutions and intron polymorphism of acetylcholinesterase1 associated with mevinphos resistance in diamondback moth, Plutella xylostella (L.) Yeh SC, Lin CL, Chang C, Feng HT, Dai SM Ref: Pestic Biochem Physiol, 112:7, 2014 : PubMed
The diamondback moth, Plutella xylostella L., is the most destructive insect pest of Brassica crops in the world. It has developed resistance rapidly to almost every insecticide used for its control. Mevinphos, a fast degrading and slow resistance evocating organophosphorus insecticide, has been recommended for controlling P. xylostella in Taiwan for more than 40years. SHM strain of P. xylostella, with ca. 22-fold resistance to this chemical, has been established from a field SH strain by selecting with mevinphos since 1997. Three mutations, i.e., G892T, G971C, and T1156T/G leading to A298S, G324A, and F386F/V amino acid substitutions in acetylcholinesterase1 (AChE1), were identified in these two strains; along with three haplotype pairs and a polymorphic intron in AChE1 gene (ace1). Two genetically pure lines, i.e., an SHggt wild type with intron AS and an SHMTCN mutant carrying G892T, G971C, T1156T/G mutations and intron AR in ace1, were established by single pair mating and haplotype determination. The F1 of SHMTCN strain had 52-fold resistance to mevinphos in comparison with the F1 of SHggt strain. In addition, AChE1 of this SHMTCN population, which exhibited lower maximum velocity (Vmax) and affinity (Km), was less susceptible to the inhibition of mevinphos, with an I50 32-fold higher than that of the SHggt F1 population. These results imply that amino acid substitutions in AChE1 of SHMTCN strain are associated with mevinphos resistance in this insect pest, and this finding is important for insecticide resistance management of P. xylostella in the field.
The use of immobilized lipase from Candida antarctica Novozym((R 435 to catalyze acetylation of trans-3,5,4'-trihydroxystilbene was investigated in this study Response surface methodology and 5-level-4-factor central composite rotatable design were adopted to evaluate the effects of synthesis variables including reaction time 24-72 h temperature 25-65 degrees C substrate molar ratio 1:15-1:75 and enzyme amount 600-3,000 PLU on the percentage molar conversion of trans-4'-O-acetyl-3,5-dihydroxystilbene The results showed that reaction temperature and enzyme amount were the most important parameters on percentage molar conversion Based on ridge max analysis the optimum conditions for synthesis were reaction time 60 h reaction temperature 64 degrees C substrate molar ratio 1:56 and enzyme amount 2,293 PLU The molar conversion of actual experimental values was 95 under optimal conditions The synthesis product was analyzed using HPLC mass and NMR The results revealed that the major product was trans-4'-O-acetyl-3,5-dihydroxystilbene The reaction kinetics was found to follow the Ping-Pong mechanism substrate inhibition was not found at high vinyl acetate concentration.
