| Selection of methamidophos resistance in the diamondback moth(DBM), Plutella xylostella (L.) from fields in Fuzhou was conducted in laborary. Compared with relative susceptible population , the resistance ratio of resistant population reAChEd 10.47-fold after 8-generation selection. The mechanism studies showed that resistance mechanism to methamidophos resistance was mainly associated with the increasing activities of Acetylcholinesterase (AChE) and carboxylesterase (CarE).The results about resistant recession of Plutella xylostella (L.) from Fuzhou indicated that in the the resistant level to cypennethrin, bisultap, methomyl, fenvalerate, chlorpyrifos, phoxim and methamidophos apparently declined four generations after being free from insecticides and the reversion ratio ranged from 1.62 to 3.68-fold. But no great difference of the susceptibility to avermectin, fipronil, chlorfenapyr, chlorfluazuron and spinosad between F| and F5 population feeding on cauliflower was found . The order of susceptibility to methamidophos of DBM reared on different host plants for 4 generations was watercress ,mustard ,cabbage , cauliflower and LC50 was 248.2K 368.88, 431.49 and 519.52 mg-L-1, respectively. In the course of resistance recession, no obvious difference in AChE actively , but great variations in CarE activity were found among DBM populations after being reared on the different species of cruciferous vegetables . The activity of the larvae feeding on cauliflower was 37.9101 x 10-2 umol/(min-mg) and was the highest, which was 2.98-fold as much as that of the larvae feeding on shanghaiqing.Susceptibilities to 13 insecticides in fuzhou DBM were monitored for 3 times from 2001 to 2002 by using leap-dip bioassay . Results showed DBM larvae were less susceptible to bisultap, methomyl, methamidophos, chlorpyriphos, phoxim , cypermethrin and fenvalerate which indicated resistance to these insecticides has occurred . However , DBM was much more susceptible to fiproniL chlorfenapyr, spinosad and avermectin . The monitoring results during 2001-2002 suggested susceptibility levels of DBM to theseinsecticides fluctuated . Most insecticides showed less toxicity to DBM , especially avermectin of which resistance ratio was 7.41-fold , while methamidophos showed more toxicity . Toxicity results tests to adults of DBM showed that fipronil and chlorfenapyr keeped highly contact toxicity and was methamidophos followed them , while other insecticides except avemectin and Bt. Which almost killed no one in experience showed less toxicity.Laboratory studies were done to evaluate differential toxicity of 13 insecticides to adults of DBM parasitoids, Cotesia plutellae Kurdj. , Oomyzus sokolowskii and Macromolen orientate by vial residual bioassays . Based on LCso the order of decreasing toxicity for C. plutellae was fipronil , methamidopho , chorpyriphos , phoxim , chlorfenapyr, avermectin, spinosad, cypermethrin, chlorfluazuron, bisultap, fenvalerate, methomyl , Bt., for O. sokolowskii it was fipronil , methamidoprK chorpyriphos , phoxim , chlorfenapyr , avermectin , cypermethrin , spinosad, hlorfluazuron, bisultap, fenvalerate, methomyl, Bt. and for M. orientate it was fipronil , methamidophos , chlorpyriphos, phoxim , chlorfenapyr , avermectin , methomyl, cypermethrin, spinosad, bisultap, fenvalerate, chlorfluazuron, Bt.. C. plutellae was more tolerant to methomyl (12.5-fold), bisultap (6.81 -fold) and fenvalerate (2.69-fold) than O. sokolowskii and also more tolerant to fenvalerate (8.58-fold), cypermethrin (3.49-fold), bisultap (6.65-fold), methomyl (24.37-fold) than M orienlale .Based on toxicity ratios (LC50 of insecticides on parasitoids / LC50 of insecticides on DBM), the selectivity indexes of insecticides were calculated . According to the selective indeses ,the insecticides were listed as follow : Bt. , spinosad, chlorfluazuron, avermectin , chlorfenapyr , fipronil , methomyl , bisultap , fenvalerate , cypermethrin, methamidoph, chorpyriphos, phoxim for C. plutellae , Bt. ,... |
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