Effect Of Chemical Insecticides On The Juvenile Hormone Esterase In Diamondback Moth,Plutella Xylostella

The diamondback moth (DBM), Plutella xylostella (L.), is a major cosmopolitan pest of brassica and other crucifer crops all over the world. Pesticide use has been the most important way in DBM control, but DBM has become highly resistant to almost all pesticides. So, it is in great necessity to find new ways to manage DBM. In this thesis, the toxicities of6chemical insecticides on DBM were tested and their effects on juvenile hormone esterase (JHE) activity were studied. Also the interaction between3-octylthio-1,1,1-trifluoro-2-propanone (OTFP) and the involved insecticides were investigated. The main results were as follows:(1) The toxicities of the6chemical insecticides on DBMThe LC50s of diafenthiuron, indoxacarb, tebufenozide, fipronil, cypermethrin, chlorfenapyr on the3rd instar larvae of DBM were135.81mg/L,8.43mg/L,331.12mg/L,1.20mg/L,585.60mg/L and5.89mg/L, respectively and those on the4th instar larvae of were196.98mg/L,9.05mg/L,426.52mg/L,1.47mg/L,754.52mg/L and6.45mg/L, respectively.(2) The effect of the6chemical insecticides on JHE in DBMAll the6tested insecticides, i.e. diafenthiuron, indoxacarb, tebufenozide, fipronil, cypermethrin and chlorfenapyr, were found to change the juvenile hormone esterase (JHE) in the3rd instar larvae and that varied with the insecticide species, insecticide concentration and experiment duration.(3) Interaction between OTFP pretreatment and6chemical insecticdes on DBMThe interaction between OTFP pretreatment and diafenthiuron, indoxacarb, tebufenozide, fipronil, cypermethrin or chlorfenapyr resulted in synergism or antagonism in the3rd instar larvae but synergism, addition or antagonism in the4th instar larvae. This indicated that the interaction results between OTFP pretreatment and insecticides varied with the insecticide species, instar of the tesed insects, OTFP concentration and experiment duration.Based on the above results, endocrine disruption by means of JHE inhibition could improve the toxicities of insecticides in certain coonditons and might be used in DBM conditions. But still more theoretical and practical work needs to be done prior to that.