Effects Of Spinosad Stress On Host Fitness Of Thrips Occidentalis

Frankliniella occidentalis is an invasive pest with a wide range of hosts,which has caused serious damage to vegetables,flowers and other crops.At present,chemical control is the most effective method to control it.So,it is important to understand the relationship between insecticide resistance and adaptability to host plants in F.occidentalis for further manage this pest.In this thesis,the toxicity of spinetoram,a common pesticide used to control thrips in the field,to F.occidentalis was determined.In addition,the insecticide resistance and biological characteristics of F.occidentalis which screened with LC₂₅ concentration of spinetoram were measured,and the adaptabilities of F.occidentalis with low resistance to spinetoram on broad bean and eggplant plants were compared.Moreover,the effects of spinetoram and hosts on the development period,life span,fecundity and survival rate of F.occidentalis were analyzed by two sex-life table.The main results were as follows:1.Effects of spinetoram on detoxification enzyme activity in F.occidentalis within a short periodThe toxicity of spinetoram to 2^nd instar nymphs of F.occidentalis was measured by leaf immersion method.The detoxification enzyme activities of F.occidentalis treated with spinetoram(LC₂₅)for 12,24,48 and 72 hours were determined respectively.The results showed that F.occidentalis was sensitive to spinetoram and LC₂₅ was only 0.0033 mg/L.After F.occidentalis was treated with LC₂₅ dose of spinetoram,the activities of CarE,GSTs,MFOs and P450s increased significantly.The changes of various detoxification enzymes were different at different time points.The activities of GSTs?MFOs and P450s reached peak at 12 h,while the activity was highest at 24 h for CarE.The results indicated that detoxification enzymes in F.occidentalis could response quickly to spinetoram.However,the response degree of different detoxification enzymes was different,and it was related to the treatment time.2.Effects of multigenerational spinetoram stress on detoxification enzyme activity,development and reproduction of F.occidentalisThe sensibility of spinetoram,detoxification enzyme activity,development period and fecundity of F.occidentalis which screened with spinetoram for 6 generations were determined.The results showed that the resistance of the 6^th generation to spinetoram was 6.4 times of that of sensitive strain.The activities of CarE and GSTs were significantly activated,which were1.26 times and 1.21 times higher than control respectively,but MFOs and P450s were significantly inhibited,which were only 54.00%and 51.78%of control.The life span,oviposition period and fecundity decreased significantly.The generation duration,longevity and oviposition period of offspring were shortened significantly,and fecundity decreased,but the female ratio increased significantly.The results indicated that the continuous screening to F.occidentalis of spinetoram not only increased the insecticide resistance and affected the activity of detoxification enzyme at different degrees,but also inhibited the development and reproduction.3.Changes of host adaptability of F.occidentalis with resistance of spinetoramThe susceptible strains and resistant strains had the significant effects on detoxification enzyme activity and the host adaptation of F.occidentalis,and had interactive effects between strain and host.When F.occidentalis fed less-preference broad bean plant,the activities of GSTs,MFOs and P450s in resistant strain were significantly higher than that of sensitive strain.When thrips fed more-preference eggplant,only the activity of CarE in resistant strain increased.For the resistant strain of F.occidentalis,the activities of GSTs,CarE,MFOs and P450s in thrips feeding on broad bean were significantly higher than that feeding on eggplant.For sensitive strain of F.occidentalis,the activity of CarE feeding on broad bean were higher than that feeding on eggplant,but the activities of MFOs and P450s were adverse.The adult longevity of resistant strain on broad bean was shorter than that of sensitive strain,the development duration of offspring was shortened,and the fecundity increased.In eggplant,the fecundity of resistant strain was lower than that of sensitive strain.However,the developmental time of offspring was significantly shortened.After resistant strain feeding on broad bean,the developmental duration was longer and fecundity was higher than that of feeding on eggplant.For sensitive strain of thrips,there is longer developmental duration on broad bean,but the fecundity was lower than that of feeding on eggplant.The index at offspring were similar.These results indicated that the adaptability of F.occidentalis could change after them were treated with spinetoram.Resistant strain of F.occidentalis increased the adaptation to less-preference broad bean,while the adaptation to more-preference eggplant weakened.It might be related to the change of detoxification enzyme activity.