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

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((R))). Mites were placed on strawberry leaf discs that were dipped in hot water. For T. urticae eggs, LT50 ranged from 250s at 47.5 degrees C to 1s at 57 degrees C, while LT100 ranged from 600s at 47.5 degrees C to 7s at 57 degrees C. For T. urticae females, LT50 ranged from 380s at 47.5 degrees C to 4s at 57 degrees C, while LT100 ranged from 1200s at 47.5 degrees C to 9s at 57 degrees C. For N. californicus eggs, LT50 ranged from 68s at 45 degrees C to 7s at 50 degrees C, while LT100 ranged from 300s at 45 degrees C to 6s at 52.5 degrees C. For N. californicus females, LT50 ranged from 107s at 45 degrees C to 6s at 50 degrees C, while LT100 ranged from 180s at 45 degrees C to 6s at 52.5 degrees C. LT(50)s 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 150s at 50 degrees C, 30s at 55 degrees C or 20s at 57 degrees 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.