Effect of hot-water treatment on the two-spotted spider mite, Tetranychus urticae, and its predator, Neoseiulus californicus (Acari: Tetranychidae, Phytoseiidae)

Abstract

Hot-water treatment has been used on various kinds of plants to control plant diseases and pests. Here, we determined the lethal times (LT50 and LT100) for various temperatures for the two-spotted spider mite, Tetranychus urticae, and the predatory mite, Neoseiulus californicus (Spical®). Mites were placed on strawberry leaf discs that were dipped in hot water. For T. urticae eggs, LT50 ranged from 250 s at 47.5°C to 1 s at 57°C, while LT100 ranged from 600 s at 47.5°C to 7 s at 57°C. For T. urticae females, LT50 ranged from 380 s at 47.5°C to 4 s at 57°C, while LT100 ranged from 1200 s at 47.5°C to 9 s at 57°C. For N. californicus eggs, LT50 ranged from 68 s at 45°C to 7 s at 50°C, while LT100 ranged from 300 s at 45°C to 6 s at 52.5°C. For N. californicus females, LT50 ranged from 107 s at 45°C to 6 s at 50°C, while LT100 ranged from 180 s at 45°C to 6 s at 52.5°C. LT50s for N. californicus eggs and females were 4–10 and 13–32 times shorter than those of T. urticae, respectively. The strawberry leaves did not appear to be damaged (i.e., they did not show significant wilting) when treated for 150 s at 50°C, 30 s at 55°C or 20 s at 57°C. Together, these results suggest that hot-water treatment can be used to control spider mites on strawberry, without much damage to the plants, but predatory mites may need to be replaced due to their sensitivity to hot water.