Study On The Integrated Control Of Two Predatory Mite Species And Acaricides Against Twospotted Spider Mite On Greenhouse Strawberry

The total output and consumption of strawberry in China rank first in the world.Strawberry industry has become a rural characteristic industry and a channel for farmers to increase their income.Strawberries are often seriously damaged by Tetranychus urticae in protected cultivation environment,which can cause 50%-80%yield reduction and bring huge economic losses to fruit farmers.With the acceleration of the green transformation of China’s development mode and the continuous improvement of people’s quality of life,biological control agents represented by predatory mites and other natural enemies of pests have been paid more and more attention,and the demand of fruit farmers for using predatory mites to control T.urticae is becoming more and more urgent.However,the application of acaricides is still an integral part of the integrated pest management（IPM）of T.urticae.In order to overcome the limitations of predatory mites and acaricides when used alone for the prevention and control of T.urticae.Coordinating the advantages of’quick effect’of chemical control and’persistence’of biological control.In this study,the T.urticae of strawberry in greenhouse was used as the control object.From the perspective of reducing the use of acaricides and saving the cost of biological control,the predation ability of two commercial predatory mites（Neoseiulus californicus and phytoseiulus persimilis）to T.urticae was determined by indoor test evaluation,and the acaricides with strong toxicity to T.urticae and relatively safe to predatory mites were screened out.Furthermore,the pot and field experiments were carried out to study the potential of the acaricide and two predatory mites to control T.urticae,which provided a control strategy and theoretical basis for the scientific prevention and control of T.urticae in strawberry production.The main findings are as follows:1.The predation functional responses of N.californicus and P.persimilis to each stage of T.urticae were studied.The results showed that the predation functional responses of the two predatory mites to each stage of T.urticae at 25°C belonged to Holling II type.The predation ability（a/Th）of N.californicus to T.urticae was as follows:larva（54.909）>protonymph（21.908）>egg（18.069）>deutonymph（17.268）>adult（0.5788）.The predatory ability（a/Th）of P.persimilis to T.urticae was in the order of egg（103.24）>larva（76.707）>protonymph（51.506）>deutonymph（44.461）>adult（0.4948）.The predatory ability of P.persimilis to T.urticae was greater than that of N.californicus.2.The study on the interference response of N.californicus and P.persimilis to their predation of T.urticae showed that N.californicus and P.persimilis had the interference of their own density on their predation when they fed on T.urticae.The equations obtained by fitting the interference response model were E=0.044P^-0.443 and E=0.056P^-0.288,respectively.The interference coefficient of N.californicus was 0.443,and the interference coefficient of P.persimilis was 0.288.N.californicus had stronger intraspecific interference when preying on T.urticae.3.The predatory selection of N.californicus and P.persimilis on T.urticae was studied.The results showed that N.californicus and P.persimilis were predatory to the eggs,larvae and protonymph of T.urticae（Q>1）,but not to the second deutonymph and female adults of T.urticae（Q<1）.4.The indoor acute toxicity of three acaricides to female adults of T.urticae was determined.The results showed that the 24 h LC₅₀ values were as follows:bifenazate（9.85 mg/L）>cyflumetofen（0.68 mg/L）>cyetpyrafen（0.09 mg/L）,the LC₅₀ values at 48 h were as follows:bifenazate（7.99 mg/L）>cyflumetofen（0.64 mg/L）>cyetpyrafen（0.08 mg/L）,indicating that cyetpyrafen had the highest toxicity to female adults of T.urticae and bifenazate had the lowest toxicity.5.The indoor acute toxicity of three acaricides to N.californicus and P.persimilis adults was determined.The results showed that the 24 h LC₅₀ values of three acaricides to N.californicus adults were as follows:bifenazate（1.67×10⁶ mg/L）>cyflumetofen（7.35×10⁵ mg/L）>cyetpyrafen（2.94×10⁵ mg/L）.The LC₅₀ values at 48 h were as follows:cyflumetofen（9.52×10⁵ mg/L）>bifenazate（1.98×10⁵ mg/L）>cyetpyrafen（1.23×10⁵ mg/L）,indicating that within 24 h,cyetpyrafen had the highest toxicity to N.californicus adults,and bifenazate had the lowest toxicity to N.californicus adults.Within 48 h,cyetpyrafen had the highest toxicity to N.californicus adults,and cyflumetofen had the lowest toxicity to N.californicus adults.Indoor acute toxicity of three acaricides to P.persimilis adults LC₅₀ values of bifenazate（3.68×10⁵ mg/L）>cyetpyrafen（1.13×10⁵ mg/L）>cyflumetofen（8.17×10⁴ mg/L）at 24 h and LC₅₀ values of bifenazate（2.81×10⁵ mg/L）>cyetpyrafen（7.67×10⁴ mg/L）>cyflumetofen（6.92×10⁴ mg/L）at 48 h were determined.The toxicity of cyflumetofen to adult P.persimilis was the highest,and the toxicity of bifenazate to adult P.persimilis was the lowest.6.By calculating the selective toxicity ratio of three acaricides against T.urticae and two predatory mites,the results showed that the selection order of three acaricides against two predatory mites was:cyetpyrafen>cyflumetofen>bifenazate.Among them,the selectivity of cyetpyrafen was the highest,indicating that cyetpyrafen was highly toxic to T.urticae,while it was relatively safe to N.californicus and P.persimilis.7.The pot experiment of combined control of predatory mites and cyetpyrafen against T.urticae was carried out.The results showed that the three control schemes had certain inhibitory effects on the population of T.urticae,and the control effects were as follows:chemical control>combined control>biological control.In the pot experiment,the effect of chemical control was the best,indicating that cyetpyrafen had better acaricidal effect.8.A field experiment on the combined control of predatory mites and cyetpyrafen against T.urticae was carried out.The results showed that the chemical control effect of cyetpyrafen alone reached 95.7%on the 7 th day,but the population of T.urticae rebounded after 14 days,indicating that the control effect of the scheme gradually decreased with the extension of investigation time.The control effect of biological control using predatory mites alone was negative on the third day.The control effect of only releasing N.californicus was-2.04%,and the control effect of only releasing P.persimilis was-4.87%.The control speed of biological control was the slowest compared with chemical control and integrated control.The integrated control schemes of cyetpyrafen combined with two predatory mites showed good prevention and control effects.On the 18 th day,the control effect was more than 90%,and there was no significant difference in the prevention and control effect of T.urticae between the combined N.californicus group（benefit-harm ratio 1:10）and the combined P.persimilis group（benefit-harm ratio 1:30）.Therefore,considering the control cost and control effect,the combination of N.californicus and cyetpyrafen was preferred.It was recommended to spray cyetpyrafen to reduce the density of mites,and release predatory mites the next day,which could be released according to the ratio of 1:10.