Temperature-Mortality Response of Eggs, Larvae, Protonymphs, Deutonymphs, and Adult Females of Tetranychus urticae (Acari: Tetranychidae)

Abstract

The two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), is one of the most important pests of cultivated plants. Its control is mainly based on the application of acaricides with concomitant adverse environmental and human health effects. Consequently, we examined the potential of using temperature as an alternative. To that end, we conducted bioassays of the temperature-mortality response of eggs, larvae, protonymphs, deutonymphs, and adult females of T. urticae. Groups of 20 individuals from each stage were placed on 4-cm diameter bean leaf (Phaseolus vulgaris L.) discs. A stream of air at the designated temperature was passed over the disc at a rate of 3.7 ± 1 m s-1) for 2 ± 1 s. Mortality was evaluated at 24 h (larva, protonymph, deutonymph, and female) or 72 h (egg) after exposure. Based on preliminary mortality responses, we selected 10 temperatures with a response range between 0 and 100% mortality. Those were 30, 35, 40, 45, 47, 50, 53, 55, 60, and 65°C [SD, ± 1.5 for each]). In total, 30 replications were conducted, and each repetition included these temperatures and untreated controls. The median lethal temperature ranged from 41.8°C for adult females to 46.9°C for eggs. The lethal temperature to kill 95% of the exposed individuals ranged from 55°C for females to 62.5°C for eggs. There were no survivors at 65°C (eggs), 60°C (larva, protonymph, and deutonymph), or 55°C (adult females).