Effects of anoxia and hypoxia on the two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae)

We investigated the potential use of anoxic (0% O-2) and hypoxic (lower O-2 concentration than in the atmosphere) conditions for controlling the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). Adult T. urticae females were exposed to O-2 concentrations of 0, 0.5, 1, 2, or 21% (control) with a constant CO2 concentration of 0.05% at 1 atm and 25 degrees C under continuous darkness for 24 h. The survival and fecundity at 8 days after treatment significantly decreased when the O-2 concentration was lower than 0.5% and 1%, respectively; the lethal concentration at 50% survival (LC50) was 0.55%. The miticidal hypoxic condition (0.5% O-2) led to physiological disorders in host plants. The degree of physiological disorders differed among the plant species tested. Although tomato seedlings died after the hypoxia treatment, in kidney bean and cucumber seedlings the primary leaves remained and lateral buds developed instead of the apical buds that ceased. Hypoxia treatment could be useful as a physical measure for controlling spider mites depending on plant species or cultivars.