Sublethal Effects Of Different Insecticides Treatments On Laodelphax Striatellus

The small brown planthopper(abbreviated as:SBPH),Laodelphax striatellus(Fallen),belongs to the family Delphacidae in order Hemiptera,which is an important pest of rice,wheat,corn,and other gramineous crops.The increased resistance of the small brown planthopper to insecticides is considered to be one of the important reasons for its outbreak and disaster.To clarify the effect of insecticide stress on the growth and development of the small brown planthopper and the mechanism of insecticide resistance,10 insecticides,including phentriazophos,carbofos,profenofos,isoprocarb,imidacloprid,thiamethoxam,nitenpyram,buprofezin,pymetrocarb and bifenthrin,were selected in this study,the indoor toxicity of 3 or 4 generations of small brown planthopper was measured by means of impregnation of rice seedings,the effects of isoprocarb and nitenpyram LC50 treatment on biological characteristics of small brown planthopper were studied by age-instar amphoteric life table.The activity changes of Carboxylesterase(CarE),glutathione-S-transferase(GST)and multifunctional oxidase(MFO)in contemporary(F0)and offspring(Fi)of SBPH were measured after treatment with 10 insecticides.The results as below:Indoor virulence results showed that,except for bifenthrin,the medium lethal concentration(LC50)of the rest 9 insecticides against SBPH showed an upward trend with the increase of their stress usage generations,and the relative resistance increased accordingly.Among them,the resistance of SBPH to nitenpyram and thiamethoxam increased by 20.11 times and 11.84 times,respectively,reaching a moderate resistance level;The relative resistance to buprofezin,phentriazophos,pymetrozine,profenofos,imidacloprid,isoprocarb and carbofos increased 4.04,3.88,2.96,2.9,2.27,2.25 and 1.59 times,respectively,and all of them were at the sensitive resistance level.Using life table method evaluate the effects of the growth and progeny of SBPH(F1,F2,F3)treated by isoprocarb and nitenpyram.After treatment with isoprocarb medium lethal concentration(LC50),the life span of female adults in the early Fi generation,the generation span of female adults in the early F2 generation and the period of the whole generation were significantly shortened,while the life span of the female adult in the early stage of F3 generation was significantly extended.After treatment with nitenpyram medium lethal concentration(LC50),the life span of prophase adults in the F1 and F2 generations was significantly shortened,while that of adults in the F3 generation was significantly prolonged,with no significant difference but a slight decrease in total life span.These results seem to indicate that the effects of isoprocarb and nitenpyram at median lethal concentration on the growth and development of the small brown planthopper experienced a process of early inhibition and then gradually decreased,that is,the small brown planthopper experienced a process from maladaptive to adaptive.After treatment with isoprocarb lethal medium concentration(LC50),the average number of first-instar nymphs hatched by the single female of F0,F1,F2 and F3 generations were increased by 23.33,81.67,131.98,181.62,respectively.After treatment with medium lethal concentration of nitenpyram(LC50),the average number of first-instar nymphs hatched by the single female of F0,F1,F2,F3 generations increased by 94.87,112.4,82.98,53.56 respectively.The activity of CarE,GST,MFO in contemporary and offspring of the small brown planthopper were measured under the treatment of 10 insecticides LC50.The results showed that,compared with the control,the activity of CarE in contemporary planthopper population was the highest in isoprocarb,and the lowest in profenofos population.The GST activity of phentriazophos population was the highest,and all treatment groups were higher than acetone control.The MFO activity of profenofos population was the highest,and all treatment groups were higher than acetone control.Compared with the contemporary age,CarE activity in the offspring of L.striatellus decreased in all treatment groups except for the increase in the population of profenofos,bifenthrin and buprofezin.GST activity increased in other treatment groups except phentriazophos population decreased.The activity of MFO decreased in all cases.It is speculated that the increase of the activity of GST in vivo may be responsible for the development of resistance.