Economic loss and control indexes of tobacco infested by Myzus persicae（Sulzer）in Guangxi tobacco-growing area

【Objective】The purpose of the study was to clarify the field control indexes for Myzus persicae(Sulzer) in the Guangxi tobacco-growing area, and to provide a scientific basis for precise prevention and control of M. persicae in Guangxi tobacco-growing area.【Method】The field cage insect infestation method was used, and the number of M. persicae was set at 5 treatments of 0(CK), 10, 50, 100 and 200 insect/plant, with 40 tobacco plants per treatment. The relationship between M. persicae number and tobacco development and growth, flue-cured tobacco leaf quality, tobacco leaf economic losses, and tobacco leaf yield losses was studied to obtain the economic threshold and ecological and economic threshold.【Result】After insect infestation, the plant height, leaf number, maximum leaf width, and maximum leaf area of tobacco plants decreased with the increase of infestation number. The insect infestation number was negatively correlated with the indexes of agronomic characters of tobacco plants. M. persicae infestation caused a significant increase in total sugar, reducing sugar, sugar-alkali ratio and nitrogen-alkali ratio(P<0.05, the same below), a significant decrease in starch, nitrogen, crude protein, nicotine and potassium contents, and no significant change in the two-sugar ratio in flue-cured tobacco leaves(P>0.05). The insect infestation number was positively correlated with total sugar, reducing sugar, two-sugar ratio, nitrogen-alkali ratio and sugar-alkali ratio, and insect infestation number was extremely significantly positively with nitrogen-alkali ratio and sugar-alkali ratio(P<0.01, the same below), and was extremely significantly negatively correlated with total nitrogen and nicotine. M. persicae infestation did not significantly reduce the comprehensive chemical composition coordination indexes of flue-cured tobacco leaves. The yield and output value of tobacco leaves decreased gradually with the increase of the number of M. persicae. When the insect number was 10, 50, 100and 200 insect/plant, the yields were 2085.30, 2023.20, 1972.80 and 1916.10 kg/ha, the yield loss rates were 1.18%, 4.21%, 6.48% and 9.11%, the output values were 57623.36, 54288.23, 51792.62 and 48987.77 yuan/ha, and the economic loss rates were 4.63%, 10.27%, 14.35% and 18.83% respectively. The economic threshold for M. persicae ranged from 11.99 to 65.50 insect/plant and the ecological and economic threshold ranged from 23.41 to 90.30 insect/plant.【Conclusion】With the aggravation of M. persicae infestation, the indexes of agronomic characters of tobacco plants show a decreasing trend, and the growth of tobacco plants gradually deteriorates. The comprehensive chemical composition coordination indexes of flue-cured tobacco leaves decreases. The yield, output value, proportion of superior and intermediate tobacco leaves and average price of tobacco leaves gradually decrease, and the yield loss rate and economic loss rate gradually increase. It is recommended that the field control index for M. persicae in Guangxi tobacco-growing area should be set at 48.76 insect/plant.