Cross-Resistance Between Tebufenozide And Abamectin And The Mechanisms In Plutella Xylostella

Diamondback moth,Plutella xylostella(L.),is a major pest of crucifer vegetables and has become particularly notorious for its resistance to various kinds of common insecticide.Owing to its polyvoltine characteristics and serious overlap of generations, this pest is easy to develop resistance to insecticides.Nowadays,there are few common insecticides that are still effective in controlling this pest.Thus,it is very important to keep P.xylostella from developing resistance to effective insecticides. Both tebufenozide and abamectin are efficient insecticides for control of this pest. Thus,some basic research must be undertacken and efficient measures for resistance management should be put into action.Based on the previous work,our study concentrated on the development of the resistance to tebufenozide and abamectin, cross-resistance between tebufenozide and abamectin,and the mechanisms in P. xylostella.The results were summarized as fellows:1.Tebufenozide resistance selection and resistance-decline in laboratory population of Plutella xylostellaA tebufenozide resistant strain of P.xylostella(RF:140) was used to select for more resistance to tebufenozide and recover its sensitivity in laboratory for evaluating tebufenozide resistance development.Results showed that after 30-generation selection with tebufenozide,no increase in resistance ratio was found.When bred without contacting any insecticides,the strain reduced its resistance,but not rapidly. The LC₅₀ to tebufenozide decreased from 2230.98ppm to 415.35ppm,but still showed 26.6 fold resistance when compared with the susceptible strain.These results suggested that the diamondback moth has the capability of developing resistance to tubufenozide,and when high resistance is developed,it is difficult for the population to recover its sensitivity to tebufenozide during a short period. 2.Abamectine resistance selection and cross-resistance testThe strain of P.xylostella with high resistance to tebufenozide and midum cross-resistance to abarnectine was used for selection of abamectine resistance in laboratory.Afer 20 generations selection,the resistance to abamectine was found to increase by 10.39 times when compared with the original and resistance radio was up to 303.77 folds compared with the susceptible strain.The cross-resistance between tebnfenozide and abamectine was also tested with the strains available.The results showed that when Teb-R was selected from ths susceptible strain by tebufenozide treatment,the resistance increased by 99.38 folds to tebufenozide and 29.25 folds to abamectine.When Teb-RD was developed from Teb-R strain by breeding without contacting any insecticides for 20 generations,the resistance to both tebufenozide and abamectine was found decreased to nearly one third of its original.However,when Aba-R was developed from abamectin treatment of Teb-R strain,the resistance to abamectine increased dramaticly,from 29.25 folds to 303.77 folds,but to tebufenozide decreased from 99.38 folds to 50.04 folds.These results indicated that tebufenozide could select cross-resistance to abamectine,but abamectine could not,which is significant for reasonable use of these insecticides in practice.3.Biochemical mechanisms conferring cross-resistance between tebufenozide and abamectin in Plutella xylostellaSynergism experiments and enzyme activity analysis have been carried out to demonstrate the mechanism conferring the cross-resistance between tebufenozide and abarnectine.The previous work in our laboratory proved that enhanced cytochrome P450 monooxygenase(MFO) is the main reason for tebufenozide resistance in the resistant strain of P.xylostella.Our results showed that PBO showed high synergism to abamectin(SR 2.11-12.23),and the synergism ratio positively related to the resistance level among different strains.Enzyme analysis also proved that the activity of MFO was notable enhanced in the strains resistant to both tebufenozide and abamectin(1.71～3.01 folds).Based on discussion,it was concluded that the major mechanism for the cross-resistance should be the enhancement of MFO activity.4.Field simulation of tebufenozide resistance development in Plutella xylostellaField simulation of tebufenozide resistance development in diamondback moth was analyzed by tebufenozide selection of a serious of laboratory populations bred from different combination of susceptible and resistant individuals.It was found that the original resistance level is higher and tebufenozide treatment also resulted in faster development of the resistance in the progeny of the combinations with higher ratio of resistant individuals.The populations with more than 5%resistant individuals could develop the resistance as high as their resistant parents after 4 generations selection by tebufenozide.These results indicated that P.xylostella has the potential to develop high resistance to tebufenozide in field.Thus,resistance minitoring and management should be put into practice.Rational use of insecticides and dilution of resistance with immigration of susceptible diamondback moth could be adopted for control of this pest.5.Molecule cloning of GluCl gene from Plutella xylostellaWith degenerate primers and RT-PCR technique,GluCI gene fragment has been successfully cloned from P.xylostella.The GluCl gene fragment is of 158 bp encoding 52 amino acids.Further analysis demonstrated that the cloned GluCi gene from P.xylostella had high identity with other insect GluCl gene previously reported, especially in Lucilia cuprina,with the similarity of 98%.This work founded the base for further study on GluCl gene and its possible target resistance mechanisms for abamectin resistance in P.xylostella.