Katayoon Kheradmand

An understanding of the impact of acaricides on predatory mites is crucial for integrated pest management (IPM) programs. The present study evaluated the sublethal effect of spirodiclofen on life table parameters of the subsequent generation of the predatory mite, Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) fed on Tetranychus urticae Koch under laboratory conditions. The sublethal concentrations LC10, LC20 and LC30 were determined based on a dose-effect assay. Exposure to the sublethal concentrations of spirodiclofen had no significant effects on developmental time of offspring of treated mites. Compared with LC10 treatment, the oviposition period of treated mites with LC20 and LC30 concentrations decreased significantly. The intrinsic rate of increase (r), finite rate of increase (λ) and net reproductive rate (R0) were not affected by sublethal concentration. Our results suggest that sublethal concentrations of spirodiclofen may not affect the population parameters of offspring from treated A. swirskii.

The experiment studied the effect of different nitrogen levels on the biology and life table parameters of the cotton aphid, Aphis gossypii Glover reared on Chrysanthemum indicum Kitan. The fertilizer treatments were administered at 0, 25, 50, 100 and 150% of the agronomic recommended concentration. The aphids were collected from greenhouses in Mahalat and transported to pots. The different nitrogen fertilizer levels did not show a specific effect on the potassium and phosphorus content in leaves. The intrinsic rate of increase and net reproductive rate ranged from 0.173 to 0.225, and 15.47 to 28.28, respectively, at different tested fertilizer levels. The aphids showed the significantly lowest mean generation time and the highest finite rate of increase when fed on chrysanthemum fertilized at a 150% fertilizer level. The aphids fecundity and survival showed a positive correlation when the fertilizer concentration was increased. On the other hand, the highest life expectancy was obtained for the aphids fed on chrysanthemum with a 25% nitrogen level. The present data suggest that plant nitrogen content is an important factor contributing to the increase severity of the cotton aphid as a pest of chrysanthemum.

Effects of the entomopathogenic fungus Beauveria bassiana were studied on life table parameters of two-spotted spider mite, Tetranychus urticae feeding on bean and cucumber under laboratory conditions. The developmental periods for all immature stages were not affected by fungal infection on each host plant but the duration of larval stage was significantly longer on bean. The female and male longevity, oviposition period and fecundity were significantly lower on fungus-treated mites but were not different between two host plants. Significant reductions were found on the intrinsic rate of increase (r m ), the net reproductive rate (R 0), the finite rate of increase (λ), the mean generation time (T c ) and the population doubling time (D t ) as a result of mycosis. Only the mean generation time (T c ) was influenced considering the effect of host plant, which was shorter on cucumber.