Effects Of Insecticides And Planting Patterns On Interspecific Competition Between Bemisia Tabaci MED And Trialeurodes Vaporariorum

Bemisia tabaci MED and Trialeurodes vaporariorum are important dominant species of whitefly on tomato crops in Yunnan Province,and they have a certain ecological niche overlap.Chemical control is an important means of controlling whitefly pests.In recent years,it has been found in most regions that there is a competitive relationship between B.tabaci and T.vaporariorum,and the role of insecticides can affect the competition between insects.In order to find out the impact of pesticides on the competition between two whiteflies,this study use the quartile method to divide the occurring period of two whiteflies in different planting patterns and growth periods,and compare the differences in the population number,occurrence peak and sex ratio of the two whiteflies in three periods.Combining the ecological niche index of the two whiteflies in different planting patterns,the competition relationship between the two whiteflies was analyzed;the toxicity of five commonly used insecticides to two types of adult whiteflies females and males was measured indoors;Exploring the survival rate and life table related parameters of the F₀generation of two types of whiteflies under the action of insecticides,with different quantity ratios and female to male ratios,and measuring the developmental duration,number of emergence,and female to male ratio of nymphs at different ages in the F₁generation of the two types of whiteflies;Determine the changes in physiological enzyme activity in the first,third,and seventh days of two species of whiteflies that compete under the action of insecticides.The main research findings are as follow:1.Daily activity pattern of B.tabaci MED and T.vaporariorumThe occurrence time of T.vaporariorum was earlier than that of B.tabaci MED in different growth stages and planting modes.The peak occurrence of B.tabaci MED was concentrated between 12:00 and 14:00,while the peak occurrence of T.vaporariorum was concentrated between 10:45 and 12:30;In early fruiting stage,B.tabaci MED in chilli fields and tomato monoculture fields have the highest population,with 31.07 ind.per sticky board and 26.62 ind.per sticky board,respectively,while T.vaporariorum population in chilli fields and cucumber fields is the highest,25.87 ind.per sticky boardand 23.67 ind.per sticky board,respectively;The highest sex ratio of B.tabaci MED was 5.35 in tomato monoculture fields during the seedling stage,T.vaporariorum in cucumber and tomato monoculture fields during the seedling stage had higher sex ratios,with sex ratios of 7.82 and 6.79,respectively;Time ecological niche index of the two whiteflies in different growth periods and planting patterns were similar,and their ecological niche overlap to a certain extent.Planting cucumbers and chilli adjacent to tomato fields can reduce the occurrence of two types of whiteflies in tomato fields.Corresponding prevention and control measures can be taken when the populations of the two types of whiteflies are low before the flowering period.2.Determination of toxicity of 5 insecticides to B.tabaci MED and T.vaporariorumThe sensitivity of female and male adults of the B.tabaci MED to these five insecticides was in the order of avermectin>sulfoxaflor>spirotetramat>imidacloprid>bifenthrin,among them,the female and male adults of B.tabaci MED have the highest sensitivity to avermectin,with LC₅₀values of 2.76 mg/L and 1.88mg/L,respectively.They have the lowest sensitivity to bifenthrin,with LC₅₀values of81.93 mg/L and 62.43 mg/L,respectively;The sensitivity of female and male adults of T.vaporariorum to these five insecticides was in the order of avermectin>sulfoxaflor>spirotetramat>imidacloprid>bifenthrin,among them,the female and male adults of T.vaporariorum have the highest sensitivity to avermectin,with LC₅₀values of 0.67 mg/L and 0.43 mg/L,respectively.They have the lowest sensitivity to bifenthrin,with LC₅₀values of 74.11 mg/L and 45.99 mg/L,respectively.Research has shown that both male and female adults of the two types of whiteflies are more sensitive to avermectin and sulfoxaflor,but less sensitive to bifenthrin.The LC₅₀values of the female adults of both types of whiteflies are higher than those of their male counterparts,while the LC₅₀values of the B.tabaci MED are higher than those of the T.vaporariorum.3.Effect of insecticide on interspecific competition between B.tabaci MED and T.vaporariorumUnder the action of avermectin,B.tabaci MED:T.vaporariorum had the shortest survival time of only 6 days in the ratio of 3:1,while B.tabaci MED:T.vaporariorum had the longest survival time of 20 days in the ratio of 1:3;The immature stage and developmental stages of the two types of whiteflies were all prolonged under the action of avermectin,the developmental stages of B.tabaci MED were shorter than those of the T.vaporariorum;Under the action of avermectin,B.tabaci MED competitive ability is superior to T.vaporariorum,and the population parameters of both types of whiteflies are significantly lower than the control.The population parameters of B.tabaci MED,F₀generation are significantly higher than T.vaporariorum,and the development duration of different insect states in F₁generation is significantly shorter than T.vaporariorum.When B.tabaci MED in the environment is dominant,especially the B.tabaci MED:T.vaporariorum is 2:1,its competitive ability is significantly improved.4.Determination of Physiological Enzyme Activities of B.tabaci MED and T.vaporariorum under the Action of InsecticidesThe LC₅₀concentration of avermectin was used to measure the activities of acetylcholinesterase,glutathione-S-transferase and Carboxylesterase in two whiteflies.The results showed that there was no significant change in the activity of the three detoxifying enzymes in the two types of whiteflies during the first,third,and seventh days of the control species.However,under the action of avermectin,the activity of the three detoxifying enzymes in the two types of whiteflies significantly increased compared to the control group on the first,third,and seventh days;The three detoxifying enzyme activities of B.tabaci MED were significantly higher than those of the three detoxifying enzymes in T.vaporariorum on the first,third,and seventh days.Research has found that B.tabaci MED can gain an advantage in competition with T.vaporariorum due to their strong detoxification enzyme activity and fast enzyme activity reaction time.