| The brown planthopper,Nilaparvata lugens Stal(Hemiptera,Delphacidae)has high fecundity,short life cycle,and strong environmental adaptability.N.lugens inhabits rice stems and sucks the phloem sap.N.lugens feeding on rice can cause slow plant growth,tillering delayed,and heavy yield loss.During outbreak years,N.lugens can lead to leaf withered and plant death in severe cases.The brown planthopper is a highly destructive rice pest on rice in China and many Asian countries.Triflumezopyrim,a novel mesoionic insecticide developed by DuPont Crop Protection,has the characteristics of high efficiency,long-lasting effect,low dosage,and environmental friendliness.Triflumezopyrim has been used to control rice planthoppers and other pests.A previous study demonstrated that seed dressing with triflumezopyrim controlled rice planthoppers’ population effectively in mechanically transplanted rice fields for a long time,but the mechanism was unclear.This paper shows 4 different concentrations of 22.5(low),45.0(medium),67.5(medium-high),and 90.0 g ai/ha(high)triflumezopyrim seed dressing treatments affect the physiological and biochemical indexes of indoor and field rice,N.lugens feeding behavior,reproduction,and field population.These changes can clarify the mechanism of triflumezopyrim as a seed coating agent for the long-term control of the brown planthopper,providing a new method for the prevention and control of brown planthopper.The results were as follows:(1)Seed dressing with triflumezopyrim affects indoor rice physiology and biochemistry indexes,brown planthopper feeding behavior,and reproduction.The results showed no significant difference in germination rate and the emergence rate of triflumezopyrim-treated seeds than control.Determination of triflumezopyrim in rice stems showed that rice stems’ residue content kept a relatively stable level(about 0.04 mg.kg-1)from 71 days to 115 days after sowing.Triflumezopyrim residue contents of gain via coated with 4 concentrations triflumezopyrim has also remained at a relatively stable level(approximately 0.015 mg.kg-1),which was far below the standard residue content(1.0 mg.kg-1).4 different concentrations of triflumezopyrim seed dressing treatments significantly affect resistant substance in rice stems and content of sucrose and free amino acids in rice stems.Compared with the control,oxalic acid in rice stems was increased by 69%～267%,and flavonoid was increased by 63%～434%via seed dressing treatments with 4 concentrations of triflumezopyrim;seed dressing with medium concentration and higher than medium concentrations triflumezopyrim resulted in phenols in rice stems was increased by 79%～159%,and callose production was increased by 139%～301%,the free amino acid in rice stems was decreased 33%～71%after treatment with 4 concentrations of triflumezopyrim.However,sucrose content in rice stems was increased by 85%～275%after seed dressing with medium concentration and higher than medium concentrations triflumezopyrim.Data of the host choice selectivity experiment indicated that the brown planthopper tended to feed on untreated rice.An electrical penetration graph(EPG)was used to analyze the effects on N.lugens female adults’ feeding behavior about triflumezopyrim-treated rice.Compared with the control,seed dressing with medium concentration and higher than medium concentrations triflumezopyrim resulted in the duration of non-penetration wave(np wave)of N.lugens female adults was increased by 56%～80%,the number of occurrences for stylet penetration into the epidermis(the number of N1 wave occurrences)was reduced by 20%～44%,and the duration of sap ingestion in the phloem(N4 wave)was reduced by 24%～71%,the number of occurrences for N4 wave was reduced by 27%～60%.Compared with the control,the treatment of medium-high and high concentration triflumezopyrim seed dressing caused the brown planthopper to reduce honeydew excretion by 19%～23%the anti-feeding effect.Seed dressing with medium concentration and higher than medium concentrations triflumezopyrim,fat body soluble protein,and ovary soluble protein of N.lugens female adults was reduced by 38%～71%and 21%～44%,juvenile hormone titer was reduced by 14%～29%,and ecdysone titer was reduced by 16%～37%,Vg expression was decreased by 46%～62%(except for medium concentration treatment),JHAMT expression was decreased by 23%～54%.Compared with the control,after seed dressing with medium-high concentration and high concentration of triflumezopyrim,the number of eggs laid by N.lugens female adults was reduced by 61%～68%,oviposition period was shortened by 53%～62%,and longevity was reduced by 51%～63%,egg hatching rate was decreased by 51%～61%.The offspring population was reduced by 22%～88%compared with the control after seed dressing with medium concentration and higher than medium concentrations triflumezopyrim.Western blot analysis showed that seed dressing treatment inhibited the synthesis of Vg protein in N.lugens female adults’ fat body.Immunohistochemical(IHC)staining showed that development of ovaries,maturation of the eggs,and Vg uptake by the ovarian tubules was inhibited when N.lugnes females fed on rice plants derived from seeds treated with high doses of triflumezopyrim.(2)Seed dressing with triflumezopyrim affects field rice physiology and biochemistry indexes,brown planthopper feeding behavior,and field population.Determination of triflumezopyrim in rice stems showed that the residue content in rice stems kept a relatively stable level(about 0.03 mg.kg-1)from 82 days to 130 days after sowing.Seed dressing treatments with triflumezopyrim affect the contents of secondary metabolites,sucrose,and free amino acids in rice stems related to brown planthopper resistance.The results showed that compared with the control,after sowing 60 days,seed dressing with 4 different concentrations of triflumezopyrim resulted in oxalic acid content in rice stems was increased by 36%～174%.Flavonoid content was increased by 58%～290%,total phenol content was increased by 89%～262%,callose content was increased by 89%～256%,free amino acid content was decreased by 23%～69%,sucrose content was increased by 37%～343%,after sowing 90 days,the oxalic acid content in the rice stems was increased by 37%～185%,flavonoid content was increased by 82%～264%,total phenol content increased by 82%～264%,and callose content increased by 61%～230%,free amino acid content was reduced by 21%～68%,and sucrose content was increased by 29%～288%.Two-factor analysis showed that there was no significant difference in the content of secondary metabolites and free amino acids in rice at 60 days and 90 days after seed dressing with 4 concentrations of triflumezopyrim.There was a significant correlation between source in rice stems and concentrations of triflumezopyrim.The relationship between source in rice stems and sowing days also showed a significant correlation.There is a significant interaction between treatment concentration and treatment days.Compared with the control,EPG data showed that after seed dressing with 4 concentrations of triflumezopyrim,the duration of non-penetration wave(np wave)of N.lugens female adults was increased by 66%～198%.The number of occurrences for stylet penetration into the epidermis(the number of N1 wave occurrences)was reduced by 37%～62%,the duration of sap ingestion in the phloem(N4 wave)was reduced by 24%～71%,and the frequency of N4 wave appearance was reduced by 34%～49%(except for low-concentration treatment).Field survey data indicated that seed dressing with 4 different concentrations of triflumezopyrim,the control effect for rice planthopper in mechanically-transplanted rice field was more than 80%after sowing 56 to 133 days in 2017.In 2018,rice planthopper’s control effect in machine-transplanted rice field was more than 93%after sowing 56d to 119d.In 2019,rice planthopper’s control effect in machine-transplanted rice field was reached 83%after sowing 62 days to 110 days.In 2020,the machine-transplanted rice field’s control effect was More than 93%after sowing 61 days to 130 days.Overall,we speculate that seed dressing with triflumezopyrim has a long-term effect on brown planthopper growth due to the synergistic effect of triflumezopyrim toxicity and changes of secondary metabolites in rice.First of all,after seed dressing with triflumezopyrim,residue content of triflumezopyrim in treated-rice plant stems is higher than sublethal concentration,which has a specific toxic effect on rice planthopper and effectively controls the rice planthopper population.Secondly,the residue content of triflumezopyrim in rice at the later stage is lower than the sublethal concentration.Due to seed dressing wjth triflumezopyrim changes in the content of secondary metabolites related to rice planthopper resistance in rice stems,rice planthoppers’ feeding behavior was inhibited,biochemical and reproductive parameters of rice planthoppers was affected.These changes reduce rice planthopper reproduction and lead to the number of rice planthopper populations in the field decrease. |
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