| Resistance of Plutella xylostella to tolfenpyrad, sublethal effect of tolfenpyrad on P.xylostella and antifeeding activity of terpenoids on P. xylostella were investigated in P.xylostella as the studying object.1. Susceptibility of Plutella xylostella to nine insecticides in different areas ofJiangxi ProvinceThe susceptibility of field populations of Plutella xylostella from eight counties inJiangxi Province to nine insecticides was bioasssyed using leaf-dip method in2013.Results indicated that8field populations of P. xylostella showed sensitive or lowresistance to Bt, chlorfenapyr and diafenthiuron, moderate and low resistance tochlorfluazuron, chlorantraniliprole and indoxcarb, and high resistance to abamectin andbeta-cypermethrin. Among the eight tested populations, the field population in Jishuishowed a high resistant level with the ratio of42.69time to spinosad, but the other sevenpopulations were moderate or low resistance with the ratio of7.06-35.12times. Therefore,Bt, chlorfenapyr, diafenthiuron, chlorantraniliprole， spinosad， indoxacarb andchlorfluazuron could be used in turn in the control process of P. xylostella in Jiangxi, andbamectin and beta-cypermethrin should be stopped.2. Resistance selection, resistance risk assessment and cross-resistance of P.xylostella to tolfenpyradThe resistance of18generations of P. xylostella to tolfenpyrad was screened in indoorusing spraying method. It showed low resistance to tolfenpyrad with the ratio of5.09timescompared with the sensitive population. The resistance of P. xylostella to tolfenpyradpresented rising trend of the curve. The heritability was0.1187using analysis method ofthreshold property, and the heritability of earlier and later stages was0.5546and0.2407,respectively. The resistance level of P. xylostella to tolfenpyrad in late development wasfaster than that in the previous. Assuming that p=0.54in indoor, required19.59to2.99generations were predicted if heritability of0.1187increased the resistance level of10times when kill ratio was50%~99%. Result indicated that P. xylostella mould produceresistance risk to tolfenpyrad. The cross-resistance of P. xylostella to eight insecticides wasassayed using leaf-dip method. The resistant population to tolfenpyrad had cross-resistanceof7times to abamectin, low cross-resistance to chlorantraniliprole, SYP-9080,flubendiamide and indoxacarb, and no cross-resistance to chlorfluazuron, diafenthiuronand chlorfenapyr. Therefore, in order to delay the resistance development of P. xylostella totolfenpyrad, using amide pesticides of the same type and abamectin was avoided.3. Resistance biochemical mechanisms of P. xylostella to tolfenpyradThe synergistic activity of three synergists, including triphenyl phosphate, piperonylbutoxide and diethyl maleate, and tolfenpyrad on susceptible and resistant populations invivo were assayed. Result showed that synergistic effect of TPP, PBO and DEM on resistant populations to Tolfenpyrad were2,1.96,1.22times, respectively, and basically nosynergistic effect on sensitive population. The detoxifying enzyme activities of susceptiblepopulation and resistant populations were assayed. Result showed that the activities ofesterase (EST), mixed function oxidase (MFOs) and glutathione-s-transferase (GSTs) wereincreased by2.14,1.32,0.95times compared with control population, respectively. Theesterase activity was highest among three enzymes, and consistent with the in vitro resultsof enzymatic activity. Therefore, detoxification enzymes involved in resistance mechanismto tolfenpyrad, and esterase works best.4. Sublethal effects of tolfenpyrad on P. xylostellaThe toxicity of tolfenpyrad to the3rdinstar larvae of P. xylostella were assayed usingleaf-dip method, and its LC30and LC50valuae of tolfenpyrad were determined based on thebioassay results. The growth and reproduction of P. xylostella and the activities of internalmixed function oxidase, esterase and glutathione-s-transferase were studied. As comparedwith the control group, the development duration of larvae and pupa of P. xylostella at theLC30and LC50concentration of the tolfenpyrad were significantly prolonged, the life-spanof adult were shortened, the larval and pupal weight and the pupation rate were obviouslydecreased, eggs laid per female and egg hatchability were significantly lower than that ofthe control group. Results indicated that the tolfenpyrad at sublethal concentrations had anegative effect on the population development of P. xylostella. Furthermore, the activitiesof3detoxifying enzymes were significantly lower than that of the control group. Theseresults showed that the detoxicification enzymes of P. xylostella could be inhibited bytolfenpyrad.5. Antifeeding activity of terpenoids to P. xylostellaThe antifeeding activities of22terpenoids to3rdinstar larvae of P. xylostella wereassayed using dipped cabbage discs. The selective antifeeding activities of22terpenoidswith the concentration at0.01g/mL were screened preliminarily. Results showed that theactivity of five samples, including No.8,12,13,19and21sample were rather high at48hafter treatment. The selective antifeeding activity to P. xylostella was assayed further with5samples at the concentrations of0.01,0.001and0.0001g/mL. Results showed that theselective antifeeding activities of No.13and21sample were higher than these of the other3samples, and antifeeding rate of No.13at the concentration of0.01g/mL was100%.Results showed nonselective antifeeding rates of No.13and21at the concentration of0.01g/mL were74.85%and68.93%at48h after treatment, respectively, lower thanselective antifeeding rates... |
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