Effects Of Nitenpyram And Thiamethoxam Seed Treatments On Aphids Aphis Gossypii And Non-Target Insects

The extensive cultivation of Bt cotton has effectively controlled lepidopteran pests such as cotton bollworm,but the piercing-sucking insects such as cotton aphid,mirid bug and whitefly has become the major insect pests in cotton fields.The neonicotinoid insecticide seed treatments can provide effective control for the piercing-sucking pests.But at the same time,it may affect the beneficial arthropods in the cotton ecosystem.In addition,the potent systemicity of neonicotinoids causes its enrichment in cotton pollen,potentially posing exposure toxicity risks to non-target insects such as honeybees at the flowering stage.Therefore,this paper compares the effects of two new neonicotinoid insecticides,nitenpyram and thiamethoxam seed coating,on the control of cotton aphid Aphis gossypii Glover?Homoptera:Aphididae?at three doses and the influence on natural enemies in cotton fields.Moreover,the dissipation dynamics of the two neonicotinoids in cotton leaves and the final residues in cotton pollen were determined.The negative effects of the two neonicotinoids on the natural enemy,seven-spotted ladybeetle Coccinella septempunctata L.?Coleoptera:Coccinellidae?,were compared in our laboratory studies.The results are as follows:1.Nitenpyram applied at 3 g a.i.kg^-1 seeds can effectively control the cotton aphid during the whole seedling stage.In the field experiments,the peaks of the number of aphids in Liaocheng and Tai'an appeared in the 41 days after sowing,which were 332 and 156 per 30plants,respectively,which were much lower than the 2218 and 3141 in the blank control.The broken rate of leaves was limited to 8%,far below the economic threshold.2.The treatment of nitenpyram and thiamethoxam seeds has a certain impact on the population of natural enemies in cotton fields?mainly seven-spotted ladybird?.At 41 days after sowing,the number of seven-spotted ladybirds in the low-concentration(2 g a.i.kg^-1 seeds)nitenpyram seed treatment area was not significantly different when compared with the blank control.The number of insects in other treatment areas was significantly lower than that of the blank control,indicating a significant negative impact.Both insecticides at 4 g a.i.kg^-1 seeds negatively affect the population of Harmonia axyridis and Propylaea japonica.The number of other natural enemies such as lacewings,hoverflies and predatory bugs in the low concentration treatment group of nitenpyram was not significantly different from that of the control group,while the high-level thiamethoxam treatment(4 g a.i.kg^-1 seeds)groups showed significant inhibitory effects.3.The dissipation dynamics of nitenpyram and thiamethoxam in leaves conform to the first-order reaction kinetics equation,and the highest residual amounts of three insecticides?nitenpyram,thiamethoxam and metabolite clothianidin?appear on the initial day for the first sampling?13 days after sowing in Liaocheng and Tai'an?.At 20 days after sowing,there was no significant difference in the residual amount of nitenpyram and thiamethoxam in the treatment of same treated level.The amount of clothianidin detected in Liaocheng and Tai'an was 1.37 and 1.56 mg L^-1,respectively,which were 0.29 and 0.32-fold lower than thiamethoxam,respectively.The half-life values of the three insecticides in cotton leaves were3.83-4.59 days for nitenpyram,4.68-5.25 days for thiamethoxam,and 8.56-9.63 days for clothianidin in the treatment groups of Liaocheng.At Tai'an,the half-life values were 8.45-9.49days for nitenpyram,8.25-10.04 days for thiamethoxam and 9.24-12.38 days for clothianidin.4.We performed descriptive statistics analysis on the final residues of nitenpyram,thiamethoxam and the metabolite clothianidin in cotton pollen.Significant dose-effect relationship can be demonstrated for the final residual amount of insectcides in the pollen of the low-level treatment(2 g a.i.kg^-1 seeds)and the high-level treatment(4 g a.i.kg^-1 seeds).There were no significant differences in pesticide residues in the pollen between the treatment group(3 g a.i.kg^-1 seeds)and the high treatment group(4 g a.i.kg^-1 seeds).At the same time,the results showed a significant correlation between the three pesticide residues in leaves and pollen at the flowering stage.We evaluated the exposure risk of insecticides to bees using a risk quotient approach.Seed treatments with nitenpyram showed acceptable risks?risk quotient:Liaocheng,0.019-0.057;Tai'an,0.015-0.052?,while the thiamethoxam treatment group possessed unacceptable risks?risk quotient:Liaocheng and Tai'an,1.45-4.66?.5.Nitenpyram posseses good compatibility with the seven-spotted ladybeetle.we evaluated the influence of nitenpyram on both larvae and adults of Coccinella septempunctata using exposure doses of 10,25,50,100,and 150%of the maximum recommended field rate?MRFR?(3,7.5,15,30,and 45 g a.i.ha^-1,respectively)and a blank control based on a preliminary acute 72-h toxicity experiment.In the long-term test,the LR₅₀?application rate causing the mortality of 50%of the individuals?of nitenpyram for C.septempunctata decreased from 73.43 to 63.0 g a.i.ha^-1,while the HQ?Hazard Quotient?values remained below the threshold value of 2.Nitenpyram did not significantly influence the survival rate,fecundity,pupation,or adult emergence at 150%of the label rate(lowest LR₅₀=63.0 g a.i.ha^-1),and its demonstrated NOER?No Observed Effect application Rates?values are all above 45 g a.i.ha^-1.Likewise,the total developmental time and egg hatchability were not significantly affected at100%of the label rate(NOER=30 g a.i.ha^-1).The assessment of the total effect?E?suggested that nitenpyram could be classified as harmless to C.septempunctata below/at a dose of 30 g a.i.ha^-1.The lowest LR₅₀ and NOER values were both above the maximum recommended field application rate of nitenpyram for controlling aphids in China.6.We evaluated the sublethal and transgenerational effects of thiamethoxam on C.septempunctata.Our results showed that thiamethoxam at doses of 0.1�LR₁₀(0.053 g a.i.ha^-1)and LR₁₀(0.53 g a.i.ha^-1)significantly reduced adult emergence,fecundity and fertility of the parental generation.In unexposed progeny?F₁?of thiamethoxam-exposed parents,at the two doses 0.1�LR₁₀ and LR₁₀,the larval stage was prolonged,and total longevity was decreased by18.76 and 24.46%,respectively.Additionally,the higher concentrations(0.1�LR₁₀ and LR₁₀)decreased the fecundity by 33.74 and 46.56%,respectively,and the oviposition period by 19.67and 25.01%,respectively.In addition,demographic parameters including the intrinsic rate of increase?r?,finite rate of increase??,net reproductive rate?R₀?,and mean generation time?T?were significantly reduced when exposed to LR₁₀.The findings of field experiments have confirmed that nitenpyram and thiamethoxam seed treatment can effectively control the aphids throughout the cotton seedling stage.And nitenpyram induced relatively little negative impacts on natural enemies in the field.Risk assessment clarified that the exposure toxicity risk of the nitenpyram seed treatment to bees was lower than thiamethoxam treatments.Furthermore,our laboratory trials demonstrated that sublethal effects of the nitenpyram exposure on C.septempunctata was less than thiamethoxam.The risk assessment suggested that nitenpyram was safe to C.septempunctata at its recommended field rates.