| The Brevicoryne brassicae L.is one of the main pests of cruciferous vegetables,and chemi-cal control using insecticides is currently the primary method for controlling this pest.To avoid the development of resistance and environmental problems caused by pesticides,it is necessary to develop and research insecticides that are highly targeted,low-toxicity,and effective in con-trolling the cabbage aphid.Flonicamid is a new type of low-toxicity pyridinecarboxamide insect growth regulator that exhibits good activity against piercing-sucking pests.However,in China,it is currently only registered for use on Brevicoryne brassicae in the form of a 50%water-dispersi-ble granule.In this study,to determine the control effect of flonicamid in different formulations on the target pest,we developed a 10%Flonicamid dispersible oil suspension based on our previ-ous research and conducted field efficacy trials on the cabbage aphid.In addition,we evaluated the sensitivity of two natural enemies,Diaeretiella rapae M’Intosh and Harmonia axyridis,to 10%Flonicamid dispersible oil suspension under laboratory conditions.The aim was to evaluate the differences in control efficacy on the Brevicoryne brassicae between 10%Flonicamid dispersible oil suspension and the existing registered 50%water-dispersible granule,and to measure the sen-sitivity of the two target insects to 10%Flonicamid dispersible oil suspension.These results will provide a reference for the registration and coordinated use of chemical and biological control methods in pest management.The main research results are as follows:1.In this study,the control efficacy of 10%Flonicamid oil-dispersible suspension concen-trate at effective dosages of 45 g/hm~2,60 g/hm~2,and 75 g/hm~2 on Brevicoryne brassicae was evaluated,using the registered 50%Flonicamid water-dispersible granule formulation(effective dosage of 60 g/hm~2)as a chemical control reference,and a treatment-free group as a blank control.The results indicated that both the aphid reduction rate and field control efficacy in the blank control group were significantly lower than those in the treatment groups.Three days after treat-ment,the field control efficacy of the treatment groups and the reference group against Brevi-coryne brassicae exceeded 75%.By the seventh day post-treatment,the control efficacies of the three treatment groups were 85.21%(effective dosage of 45 g/hm~2),88.23%(effective dosage of60 g/hm~2),and 90.98%(effective dosage of 75 g/hm~2),respectively.When the 10%Flonicamid dispersible oil suspension was applied at a dosage of 45 g/hm~2,the aphid reduction rate and field control efficacy from days 1 to 5 post-treatment exhibited no significant difference compared to the reference treatment,whereas the efficacy on day 7 was higher than that of the reference group.When the 10%Flonicamid dispersible oil suspension was applied at dosages of 60 g/hm~2 and 75g/hm~2,the aphid reduction rate and field control efficacy demonstrated no significant difference compared to the reference treatment during days 1 to 3 post-treatment,but were significantly higher than the reference group during days 5 to 7.2.The results of the laboratory toxicity experiments showed that the LC50 values of floni-camid for three tested insects were 0.97 mg/L for Brevicoryne brassicae,8.61 mg/L for second instar larvae of H.axyridis,and 53.56 mg/L for Encarsia formosa.The safety evaluation of the pesticide on natural enemies showed that the safety coefficient of 10%Flonicamid dispersible oil suspension dispersible oil suspension to Encarsia formosa was 1.19,indicating low risk,while the safety coefficient for second instar larvae of H.axyridis was 0.19,indicating high risk.This indi-cates that the pesticide has a higher safety profile for D.rapae.The benefit-to-harm ratios of the tested pesticide on Encarsia formosa and H.axyridis were 55.22 and 8.88,respectively,indicating that the pesticide is favorable for integrated pest management that combines biological control with chemical control.3.The exposure of adult D.rapae to pesticides during the parasitoid wasp’s life cycle has a significant negative impact on the longevity of both male and female wasps.Specifically,the female wasp’s lifespan decreased from 18.33 days in the control group to 13.29 days in the pesti-cide treatment group,while the male wasp’s lifespan decreased from 11.29 days in the control group to 5.67 days in the pesticide treatment group.However,pesticide treatment did not have a significant adverse effect on the reproduction and offspring fitness of D.rapae.The total number of eggs laid by a single female wasp after pesticide treatment was 259.52,which was not signifi-cantly different from the control group with 310.64 eggs.The emergence rate and sex ratio of offspring in the control group were 90.08%and 78.72%,respectively,while those in the pesticide treatment group were 87.82%and 81.12%,respectively.There was no significant difference in the emergence rate and sex ratio of offspring between the two treatment groups.4.Exposure of second instar larvae of H.axyridis to 10%Flonicamid dispersible oil suspen-sion significantly reduced the cumulative survival rates of third and fourth instar larvae and pupae,but not of first and second instar larvae,compared to the control group.The cumulative survival rate of pupae in the pesticide treatment group was significantly lower than that of larvae,while there was no significant difference in the cumulative survival rate of larvae and pupae between the control group.Additionally,the pesticide treatment of second instar larvae resulted in a nega-tive effect on the growth of surviving individuals of H.axyridis,as evidenced by a significant extension of the duration of third instar and a significant decrease in the weight of pupae.The pesticide treatment did not have a significant negative impact on the pre-oviposition period of H.axyridis females,but a reproductive analysis conducted over 10 days showed that the mean num-ber of eggs laid per female per day in the pesticide treatment group(258.87 eggs/day)was signif-icantly lower than that of the control group(332.44 eggs/day).The control group also exhibited a significantly higher daily peak oviposition rate(35 eggs/day)compared to the treatment group(28eggs/day),and the daily egg laying rate of the control group was significantly higher than that of the pesticide treatment group throughout the entire investigation period.In summary,this study confirms the field control effect of 10%Flonicamid dispersible oil suspension on the cabbage aphid and recommends a suitable field application rate.Furthermore,laboratory toxicity and sensitivity experiments were conducted to determine the potential impact of the pesticide on two natural enemies. |
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