| Diamondback moth, Plutella xylostella(L.)(Lepidoptera: Plutellidae), is one of the most destructive pest around the world. Until now, synthetic insecticides are still the major tools for controlling this pest. However, P. xylostella has developed resistance against various insecticides because of its short lifespan, high reproduction, and the high selection pressure with insecticides. The anthranilic diamide are a new class of insecticides to control P.xylostella with a novel mode of action by binding the ryanodine receptors(RyR), activating the unregulated release of internal calcium stores, causing feeding cession and muscle paralysis, and finally triggering the death of the insect. It becomes one of the most popular insecticides because of its good control over insects, and low toxicity to beneficial arthropods.But high levels of resistance appear soon. In the present study, we investigate the mechanism and characteristics of the resistance to chlorantraniliprole in P. xylostella, as well as the sublethal effect of cyantraniliprole to P. xylostella. The results were as follows:1. After 52 generations of selection with chlorantraniliprole, about 48.2-fold resistance was observed in P. xylostella. In the selection process, the resistance development speed of the first 8 consecutive generation selections was slow. Then the resistance in the following selection speeds up. The chlorantraniliprole resistance in P. xylostella was not stable. When maintaining the resistant strain in the lab without contacting any insecticides for 6 generations,the resistance ratio decreased to 14.9.2. The chlorantraniliprole-resistant strain was used to examined the cross-resistance to other insecticides. The resistant strain showed cross-resistance to flubendiamide(7.29-fold)and cyantraniliprole(3.31-fold), but no cross-resistance to chlorpyrifos, beta-cypermethrin,emamectin benzoate, chlorfenapyr, spinosad, hexaflumuron and tebufenozide. When controlling pest in the field, rotation of the insecticides that do not have cross-resistance with chlorantraniliprole may be applied.3. Reciprocal crosses were made between the susceptible and resistant strain. Then we measured the toxity of chlorantraniliprole to F1 progency of reciprocal crosses. The results suggested chlorantraniliprole resistance in P. xylostella was autosomal, and incompletely dominant. No distinct plateau corresponding to 50% mortality was observed in the LD-Pcurve of the backcross progency to chlorantraniliprole. It suggested chlorantraniliprole resistance in P. xylostella was controlled by two or more genes. The test of monogenic inheritance also approved the result.4. The life table of P. xylostella was built to study the relative fitness of the chlorantraniliprole-resistant strain. The results showed relative finesses of the resistant strain was 0.77 when compared with that of the susceptible strain. In addition, the duration of larvae was about 1.5d prolonged, and the duration of pupae was also delayed in the resistant strain.The pupation rate, adult emergence rate, the number of eggs laid per female, R0 and rm were lower in the resistance than that in the susceptible strain.5. In the study, the activities of cytochrome P450, GST and EST in the resistant strain were compared with that of the susceptible strain. The activity of cytochrome P450 was 4.26 fold higher in the resistant strain than the susceptible strain, but no differences for activities of GST and EST were found in the two different strains. The effects of PBO, DEM, and DEF on chlorantraniliprole were investigated. The results showed PBO could increase the toxicity of chlorantraniliprole to P. xylostella. Further study found cytochrome P450 genes, including CYP6BF1V1, CYP6BG1 and CYP6CV2, increased about 8.9, 3.5 and 3.2-fold, respectively,in the resistant strain. So we inferred these three genes may play an important role in the resistance of chlorantraniliprole to P. xylostella.6. To study the target resistance mechanism of P. xylostella to chlorantraniliprole, we cloned a full-length cDNA sequence about 15,643 bp of the ryanodine receptor. The full-length cDNA contained a full open reading frame(ORF) of 15, 372 bp. Total 5, 123 amino acids residues were predicted by the ORF. After analysis of the amino acid sequence of PxRyR with other 20 sepcies, we constructed the evolution tree by MEGA 4.0. There were five essential transmembrane segments predicted from the secondary structure of the deduced amino acid sequence, which formed the functional Ca2+ channel. In addition, the modify of RIH, inositol 1,4,5-trisphosphate and ryanodine receptor, MIR etc. were found in PxRyR. In my study, no amino-acid substitution was found in the two different strains. But the expression level of the RyR gene in the resistant strain was about six fold higher than that expressed in the susceptible strain.7. Two insecticide treatments(LC20=0.03mg/L, LC50=0.08mg/L) were applied to P.xylostella for 48 h to study the effect of cyantraniliprole on the insect. Exposing larvae to cyantraniliprole could extend the duration of 4th instar larvae and pupae, and reduce the pupation rate and adult emergence rate. This effect was also dose related. The weight of insecticide-treated pupal was significantly lower compared with the control, and there were no significant differences between the two insecticide treatments. In addition, LC50 of cyantraniliprole significantly reduced the number of eggs laid per female, but no difference was found between LC20 treatment and the control. The effect of cyantraniliprole on the biological characteristics of first generation of offspring was also tested. The results showed there was no effect on the offspring except the prolonged duration of eggs in the LC50 treatment. |
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