Temperature Effects on the Efficacy of Phytoseiulus persimilis and Amblyseius swirskii (Acari: Phytoseiidae) Against Tetranychus urticae (Acari: Tetranychidae) in Strawberry Crops

The two-spotted spider mite, Tetranychus urticae Koch, is a major arthropod pest that causes substantial economic losses in strawberry and other crops worldwide. Its management often relies on intensive acaricide applications, which may negatively affect human health, the environment, and beneficial organisms. Biological control using predatory mites has been widely adopted under greenhouse conditions, and its success is influenced by several factors, particularly temperature, T. urticae population density, and predator release methods. During the 2023–2024 season, this study evaluated the effects of ambient greenhouse temperature on the population dynamics of T. urticae and on the efficacy of two phytoseiid predators, Phytoseiulus persimilis (Athias-Henriot) and Amblyseius swirskii (Athias-Henriot). The predators were released individually and in combination on strawberry plants. The efficacy of single and combined releases was assessed under three temperature ranges: 25–27 °C, 28–30 °C, and 30–32 °C. The results showed that the mean number of motile T. urticae per plant increased from 21.7 to 95.66, while the mean number per leaf increased from 2.33 to 6.05 during the experimental period. The mean greenhouse temperature ranged from 23.83 °C to 31.88 °C. Temperature was strongly and positively correlated with T. urticae population density, with higher temperatures generally accelerating development and population growth. Both predator species, whether released individually or in combination, significantly reduced T. urticae populations compared with untreated control plants. Amblyseius swirskii demonstrated greater efficacy than P. persimilis at temperatures above 28 °C. However, the combined release consistently achieved the highest level of mite suppression across all temperature ranges. Significantly greater population reduction was observed at approximately 25–26 °C compared with single-species releases, while maximum effectiveness occurred at temperatures above 28 °C. These findings indicate that the combined use of P. persimilis and A. swirskii represents an effective biological control strategy for managing T. urticae in greenhouse-grown strawberries, particularly under elevated and fluctuating temperature conditions.