| The western flower thrips (WFT), Frankliniella occidentalis (Pergande) invaded in China in2003, and became one of the major pests of vegetable, fruit and ornamental crops. In order to understand the insecticide resistance risk and rsistance mechanism of F. occidentalis in China, the insecticide resistance levels, cross-resistance and resistance mechanisms to imidacloprid, emamectin benzoate and phoxim resistance were studied. The results are as follows:1. The effects of different conditions on the laboratory bioassay results with spinosadThe effect of environmental factors such as temperature, relative humidity (RH), water quantity, photoperiod, illuminance and leaf on the results of laboratory bioassay of spinosad to F. occidentalis was studied using method of Munger cell. The results showed that during the bioassay conditions ranges of temperature25-30℃, RH50%-70%, water quantity0.5-1.5mL, photoperiod16:8-24:0(L:D), illuminance6500-13000lx and with the leaves of Rosa chinensis, Cucurbita pepo, Raphanus sativus, Phaseolus vulgaris, Malus pumila mill, Apiumgraveolens, Spinacia oleracea, the laboratory bioassay results preserve stationary. The leaf cilium density has negative correlation with the bioassay result of spinosad to F. occidentalis, the length of leaf cilium has no correlation with the bioassay result.2. Insecticide resistance levels of difenrent populations of F. occidentalisInsecticide resistance of F. occidentalis was determined by Munger cell method. The BJ, SG, JN, CG and QD populations was collected from sweet pepper (BJ, SG and QD) and rose (JN and CG) greenhouse in Beijing, Shouguang, Qingdao, Jinning and Chenggong. Bioassays against spinosad, chlorpyrifos, avermectins, emamectin benzoate, lambda cyhalothrin, chlorfenapyr, methomyl, imidacloprid and acetamiprid were conducted. The results showed that the level of resistance to spinosad was significant (RR5O>30) in BJ, JN and CG populations, imidacloprid in SG population, and acetamiprid in QD population. We also studied enzymes activity of pooled insects both in susceptible (S) population and in BJ, SG, JN, CG and QD populations, which are classically related to detoxification of insecticides: carboxylesterase (CarE), glutathione S-transferase (GST) and mixed function oxidase (MFOs). Significant increases in the enzyme mean activity were found between field populations and S population.3. Resistance mechanism of F. occidentalis to imidacloprid and cross-resistance to other insecticidesAfter32times selections, F. occidentalis developed medium level of resistance on imidacloprid (resistance ratio of13.91times). Imidacloprid showed low levels of cross-resistance to abamectin, emamectin benzoate, cyhalothrin, methomyl and chlorpyrifos. The synergists DEF (s, s, s-tributyl phosphorotrithioate), TPP (triphenyl phosphate) and DEM (diethyl maleate) had significantly synergism on the toxicity of imidacloprid in the resistant population (BK). In vitro assays of enzyme activities showed significantly increased activity of CarE (5.05-fold) and GST (1.63-fold) in the BK populations, indicating that an enhanced detoxification was responsible for the imidacloprid resistance in F. ocddentalis.4. Resistance mechanisms of F. ocddentalis to emamectin benzoate and cross-resistance to other insecticidesIn order to evaluate the resistance risk of emamectin benzoate to F. ocddentalis, the cross-resistance and biochemical resistance mechanisms of emamectin benzoate resistant population (JK) were investigated by the methods of Munger cell, synergist and enzyme activity assay. The results showed that F. ocddentalis developed a medium level of resistance on emamectin-benzoate (resistance ratio of39.32times) after24times selections. The JK population had medium level of cross-resistance to abamectin with31.656-fold, medium level of cross-resistance to acetamiprid with12.182-fold, low level of cross-resistance to imidacloprid, chlorfenapyr, cyhalothrin, chlorpyrifos and methomyl with5.517-8.568-fold, yet no cross-resistance to spinosad. The synergists piperonyl butoxide (PBO), DEM, DEF and TPP all had significant synergism to the JK and SG populations. Compared with the S population, the JK population had significantly increased contents of cytochrome P450and b5, activities of mixed-functional oxidases O-demethylase, GST and CarE with3.89,3.61,5.32,4.42and1.30fold increase, respectively. Therefore, it was inferred that the increased detoxification enzyme activities such MFOs, GST, CarE and so on may play an important role in the resistance of F. occidentalis to emamectin benzoate.5Resistance mechanisms of F. occidentalis to Phoxim and cross-resistance to other insecticidesCross-resistance and resistance mechanisms of phoxim resistant population (XK) of F. occidentalis were studied. The results showed that F. occidentalis developed medium level of resistance on phoxim (resistance ratio of30.33times) after32times selections. The XK population had medium levels of cross-resistance to chlorpyrifos, cyhalothrin and methomyl, and the low level of cross-resistance to chlorfenapyr, imidacloprid, emamectin-benzoate and spinosad, but no cross-resistance to acetamiprid and abamectin. The synergists PBO, DEF and TPP had significant synergism (P<0.05) on the toxicity of phoxim to the XK, BJ and S populations. The DEM had no significant synergism to XK and S populations but had significant synergism to BJ population. Compared with the S population, the XK population had significantly increased activities of mixed-functional oxidases P450(2.79-fold), b5(2.88-fold), O-demethylase (2.60-fold), CarE (2.02-fold). The results indicated that the increased activities of MFO and CarE might play an important role in the resistance of F. occidentalis to phoxim. |
PDF Full Text Request