Physiological Response of Cotton Plants to Feeding of Three Tetranychus Spider Mite Species (Acari: Tetranychidae)

Laboratory and greenhouse studies with cotton leaves were done with densities (mites per cm2 per day) of 1,2,4,8, and 16 Tetranychus turkestani Ugarov & Nikolski, T. urticae Koch, and T. pacificus McGregor to determine mite density effect on stomatal and mesophyll resistance to water vapor and 14CO2 diffusion and rates of photosynthesis. T. turkestani, by far the most injurious species, caused significant reduction of water vapor diffusion, CO2 uptake, and photosynthetic rate at one mite per cm2 per day compared with the presence of no mites. T. pacificus was somewhat more injurious than T. urticae; significant reduction of the parameters began at two mites per cm2 per day compared with the presence of no mites. The results indicate strongly that T. turkestani has a toxin-induced injury to cotton in comparison with the other two species.