[Damage and economic threshold of the third generation of cotton bollworm in the Yangtze River basin cotton region of Jiangsu Province].
The impact of the third generation of cotton bollworm Helicoverpa armigera on shedding of buds and bolls and on bolling was studied by inoculating its larvae to cotton plants. The results showed that the shed rate of buds and bolls damaged by the larvae had the greatest impact on bolling, and its direct path coefficient was up to -0.8917. The larval population density and the number of buds and bolls damaged by the larvae impacted bolling mainly through the damaged shed rate during inoculating stage, and their indirect path coefficients were -0.8894 and -0.891 respectively. Both of the direct and indirect path coefficients of natural shed rate during inoculating stage to bolling were small, which showed that the cotton had little capacity of compensation while the third generation cotton bollworm occurring. The investigations of damage number by larvae showed that the damage equivalent of the 1st-6th instar larval were 0.02, 0.14, 0.31, 0.47, 0.84 and 1.54 old bolls respectively. Based on direct and indirect benefits from controlling, the economic threshold of the third generation of the bollworm was worked out to be 26 accumulated eggs per 100 plants.
Yang
Y
Y
Tongzhou Plant Protection Station, Jiangsu Province, Tongzhou 226300.
Wang
D
D
Zhu
M
M
D000383:Agriculture; D000818:Animals; D002681:China; D005247:Feeding Behavior / Q000502:physiology; D003368:Gossypium / Q000191:economics* / Q000469:parasitology*; D007814:Larva / Q000502:physiology; D007915:Lepidoptera / Q000502:physiology*; D010063:Ovum / Q000502:physiology