Evaluate the efficiency of releasing two predatory species at their optimal temperature for controlling Tetranychus urticae (Acari: Tetranychidae) in a croton greenhouse

Croton, Codiaeum variegatum L., is a beautiful tropical plant. The two-spotted spider mite, Tetranychus urticae Koch, causes economic damage to croton. The present study aimed to control T. urticae by releasing two predatory species, Phytoseiulus persimilis Athias-Henriot and Stethorus punctillum Weise, at the optimal temperature and humidity for each predator. The experiments were carried out in commercial plastic greenhouses for two seasons. Once the T. urticae infestation was detected, the predators were released. Phytoseiulus persimilis was released three times, with a rate of 9/m2. Its population increased when the temperature and humidity ranged from 25.5–29 °C and 72.8–86.4% RH, respectively, while it disappeared when the temperature increased above 30 °C. There was a negative correlation between P. persimilis and temperature and a positive correlation with relative humidity. Stethorus punctillum was released twice, at a rate of 0.5/m2. Its population increased when the temperature and humidity ranged from 31.8–35 °C and 65–77% RH, respectively. There was a positive correlation between S. punctillum and temperature and a negative correlation with relative humidity. In the two seasons, the population of T. urticae decreased gradually to nil/croton leaf in the biological greenhouse while increasing to 59.47 ± 6.34 and 85.63 ± 10.45 mites/croton leaf in the control greenhouse in 2019 and 2020, respectively, at the end of the season. The combination of the two predators was able to achieve effective control of T. urticae when used according to the optimal temperature for each predator in croton greenhouses.