Persian Journal of Acarology

Abstract The predatory mite Amblyseius swirskii is widely used as a biological control agent against spider mites, thrips, and whiteflies. This study examined the sublethal effects of two abamectin concentrations (LC10 and LC20 for A. swirskii) on life history traits and demographic parameters of the F₁ generation derived from treated parents under controlled laboratory conditions (25 ± 1 °C, 75 ± 5% RH, 16:8 [L:D] photoperiod). Using the age-stage, two-sex life table approach with Tetranychus urticae Koch as prey, results showed that total longevity was shortest in progeny of LC20-treated parents (males = 13.42 days; females = 13.94 days) compared with LC10 progeny (males = 15.06 days; females = 15.50 days). Fecundity, oviposition period, and net reproductive rate (R₀) declined significantly with increasing acaricide concentration. Intrinsic and finite rate were reported to be increased in the treatments (r: 0.159 vs. 0.199 day−¹; λ: 1.172 vs. 1.221 day−¹). Age-specific survival (lₓ), fecundity (mₓ), and reproductive value (vₓⱼ) curves indicated pronounced adverse effects of sublethal exposure on population performance. These findings demonstrate that even low concentrations of abamectin can compromise key life history traits of A. swirskii, potentially limiting its effectiveness in biological control programs. Thus, evaluating acaricide compatibility with natural enemies is critical for successful IPM implementation.

Abstract Two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) is an economically important pest that devastates varieties of crops worldwide and develops significant resistance to common chemical pesticides. Ovicidal effects of two isolates of entomopathogenic fungus, Beauveria bassiana (Balsamo) Vuillemin (isolates F and J.B.) were evaluated on the eggs of T. urticae using a spray method at 25 ± 2°C, 60–70٪RH and a photoperiod of 16:8 h (L: D). Egg mortality was determined by using different concentrations of conidia (1 × 10³, 1 × 10⁴, 1 × 10⁵, 1 × 10⁶, 1 × 10⁷, and 1 × 10⁸ conidia/ml). Mortality was found to increase with time and was dependent on time and conidia concentration, ranging from 4.06% on day 3 at a concentration of 1 × 10³ to 84.37% on day 7 at a concentration of 1 × 10⁸ for the F isolate and from 1.87 to 65% for the J.B. isolate, respectively. This study also investigated the direct spray of the entomopathogenic fungus, Beauveria bassiana (isolates F and J.B.) on the predatory mite, Phytoseiulus persimilis (Athias-Henriot) under laboratory conditions. The predator adults were susceptible to isolate F (total mortality ± SE: 35 ± 1.97% on the seventh day) but least susceptible to isolate J.B. (total mortality ± SE: 27.25 ± 1.33% on the seventh day). Moreover, viability of P. persimilis after spraying fungal isolate of J.B. on bean leaf discs at three time intervals (0, 24 and 48 hours) showed no significant difference. Further knowledge is needed to adjust the timing of various releases of both biological control agents to obtain maximum effectiveness in the greenhouse with minimum impact of the fungus on the predator.