Effect Of Three Insecticides On The Predatory Potential Of Arma Chinensis (Hemiptera:Pentatomidae) Nymphs To Ectropis Grisescens (Lepidoptera:Geometridae) Larvae

Ectropis grisescens is an important leaf-feeding pest of Lepidoptera in tea plantations.When the firestorm of E.grisescens happened,the tea leaves were eaten up,which seriously affected the yield and quality of tea.At present,the management of E.grisescens relies primarily on the application of insecticides,which have a great negative influence on its natural enemies and result in the increase of insecticide resistance and the decrease of the number of natural enemies.It has been shown that A.chinensis is a crucial predator of geometers in tea plantations,but there are few reports on the effects of insecticides on A.chinensis in tea plantations.Therefore,in order to discuss the effect of commonly used chemical insecticides on A.chinensis in tea plantations,this thesis researched the toxicity and safety evaluation of A.chinensis and E.grisescens concerning three insecticides:bifenthrin,chlorfenapyr and emamectin benzoate,the influence on the predation functional response of A.chinensis,the effect on the survival and fecundity of the parent A.chinensis.Then the two-sex life table of the F₁ generation of A.chinensis was constructed.It had the goal of illuminating the influence of insecticides on A.chinensis to E.grisescens,providing practical guidance for releasing A.chinensis and using insecticides to prevent and control E.grisescens in tea plantations,and promoting high-quality,stable,and sustainable development of the tea industry.The main results and conclusions are as follows.（1）The laboratory toxicity and safety evaluation of three insecticides against A.chinensis and E.grisescensThe laboratory toxicity of three insecticides to Arma chinensis and E.grisescens was determined by the leaf dipping method.The maximum practical concentrations of three insecticides in farmland were used as the initial concentrations.The results showed that the mortality rate of three insecticides against A.chinensis 1^st～4^th instar nymphs was more than 80%,indicating that three insecticides were unsafe to A.chinensis 1^st～4^th instar nymphs.The mortality rate of three insecticides against A.chinensis 5^thinstar nymphs arranged from high to low as:emamectin benzoate（66.7%）>bifenthrin（55.0%）>chlorfenapyr（31.7%）,indicating that bifenthrin and emamectin benzoate were unsafe to A.chinensis 5^th instar nymph.However,chlorfenapyr was relatively safe to A.chinensis 5^thinstar nymph.The sublethal effects LC₅₀（48 h）of bifenthrin,chlorfenapyr,and emamectin benzoate on the 5^th instar nymph of Arma chinensis were9.947、311.701、31.262 mg·L^-1 respectively,on the 2^nd instar larva of E.grisescens were 14.638、0.004、0.058 mg·L^-1 respectively.According to calculating the ratio of LC₅₀ of A.chinensis to E.grisescens,it showed that the Selectivity Toxicity Ratio（STR）of three insecticides to the 5^thinstar nymph of A.chinensis was more than 1,i.e.,all three insecticides showed positive selectivity to the 5^th instar nymph of A.chinensis.In conclusion,the effects of bifenthrin,chlorfenapyr,and emamectin benzoate were more toxic to A.chinensis and less lethal to E.grisescens when spraying three chemical insecticides and releasing A.chinensis.（2）Effects of sublethal concentrations of three insecticides on the predatory functional response of the 5^th instar nymph of A.chinensisThe effects of the predation functional response of Arma chinensis by utilizing sublethal doses LC₂₀ of three insecticides,bifenthrin,chlorfenapyr,and emamectin benzoate,showed that the predation functional response models of the 5^th instar nymph of A.chinensis were still conformed to the HollingⅡmodel,in spite of the parameters of models had some changes.The handling time（T_h）of the 5^th instar nymph of A.chinensis against 2^nd and 3^rd instar larvae of E.grisescens was prolonged,and the daily maximum consumption predation(N_{a max})and predation capacity（a/T_h）were decreased.The instantaneous attack rate（a）and predation capacity（a/T_h）of the 5^th instar nymph of A.chinensis against 4^th instar larva of E.grisescens were increased,and in chlorfenapyr treatment,the handling time（T_h）shortened（0.1070 d）,while the predation capacity（a/T_h）（14.3495）and the daily maximum consumption predation(N_{a max})(9.35 individual·box^-1)increased;as the density of E.grisescens increased,the searching efficiency（S）of A.chinensis 5^th instar nymphs decreased.To sum up,bifenthrin,chlorfenapyr,and emamectin benzoate had a negative effect on the predation of the 5^th instar nymph of A.chinensis against 2^nd and 3^rd instar larvae of E.grisescens,while chlorfenapyr had a positive effect on the predation of the 5^th instar nymph of A.chinensis against the 4^th instar larva of E.grisescens.（3）Effects of sublethal concentrations of three insecticides on the 5^thinstar nymph and F₁ generation population of A.chinensisBased on determining the 5^th instar nymph of Arma chinensis by leaf dipping,it was shown that three insecticides decreased the eclosion rate,survival rate and longevity of nymphs and adults,and fecundity（F）.Then the sublethal effects of bifenthrin,chlorfenapyr and emamectin benzoate at the sublethal concentration(LC₂₀)on the F₁ generation population were studied by building age-stage,two-sex life table,compared to control,bifenthrin significantly prolonged the developmental duration of the 1^stinstar nymph（4.08 d）of F₁ generation of A.chinensis,while significantly shortened the developmental duration of the 2^nd instar nymph（4.96 d）and the age of 50%mortality（13.00 d）;chlorfenapyr significantly prolonged the developmental duration of eggs and the 2^nd instar nymph of A.chinensis（7.75 d、6.48 d）,while significantly shortened the developmental duration of 1^st instar nymph and the total nymphs（3.06 d、28.53 d）;emamectin benzoate significantly shortened the developmental duration of eggs and the 2^nd instar nymph of A.chinensis（6.65、4.81 d）,and significantly prolonged and adult preoviposition period（APOP）（9.50d）.However,in four treatments,some population life table parameters of the F₁ generation of A.chinensis were not significantly different,which included preadult duration,preadult survival,adult longevity,female adult longevity,male adult longevity,total preoviposition period（TPOP）,oviposition days（O_d）,total longevity,and mortality distribution（SASD）,age-stage specific life expectancy(e_xj),age-stage specific reproductive values(v_xj),fecundity（F）,proportion of female adults（N_f/N）,net reproductive rate（R₀）,intrinsic rate of increase（r）,finite rate of increase（λ）,mean generation time（T）.According to studying the consumption rate of the F₁ generation population of A.chinensis,the results showed that,compared to control,bifenthrin significantly decreased the mean daily predation of preadults,adults,and female adults of A.chinensis(0.866、3.563、3.510individual·d^-1).The mean daily predation of the 3^rd instar nymph was significantly reduced by emamectin benzoate(2.304 individual·d^-1),whereas the mean daily consumption in the chlorfenapyr treatment was not significantly different.After preying on E.grisescens,the cumulative net consumption rate（C_x）of A.chinensis increased first and then tended to level off;the age-specific consumption rates（k_x）and the age-specific net consumption rates（q_x）increased first and then decreased;the net consumption rate（C₀）decreased;but the stable consumption rate（ψ）and the finite consumption rate（ω）were not significantly different among four treatments.According to the timing population simulation modeling,the offspring population of A.chinensis could maintain growth when treated with three insecticides.After 120 d,compared with the control（234 individuals）,the population sizes under bifenthrin treatment（17individuals）,chlorfenapyr treatment（97 individuals）and emamectin benzoate treatment（23 individuals）decreased by 92.74,58.55,and 90.17%respectively.The total predation rate of A.chinensis was predicted by the timing consumption simulation modeling.It was found that the total predation rate of A.chinensis was the highest（380 individuals）in control treatment after 120 days,followed by 141 individuals in chlorfenapyr treatment,30 individuals in both bifenthrin treatment and emamectin benzoate treatment.The results indicated that chlorfenapyr was a relatively less unsafe insecticide on F₁ and offspring populations of A.chinensis compared with bifenthrin and emamectin benzoate.In conclusion,chlorfenapyr and A.chinensis were recommended for use together to control E.grisescens in tea plantations,which in order to control E.grisescens in tea plantations reasonably and minimize the damage of insecticide to A.chinensis.