Effect of methoprene on the heat tolerance and cold tolerance of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Methoprene, a Juvenile Hormone analogue, was evaluated for its ability to alter heat tolerance or cold tolerance of Tribolium castaneum, the red flour beetle. Young adults and late instar larvae were exposed to a series of methoprene concentrations. They were held either at 46 °C or 0 °C for different durations, and survival of adults or the adult emergence from larvae was recorded to determine their tolerance to extreme temperatures. At 46 °C, the lethal time to kill 50% of the population (confidence intervals) for untreated adults was 10.8 (9.6–11.8) h compared to 9.3 (8.3–10.0) h for adults exposed to 3.33 ppm of methoprene for 48 h. Higher concentrations of methoprene also caused adults to be less heat tolerant. In contrast, there was no evidence that methoprene reduced the heat tolerance of larvae. At 0 °C, both unacclimated and cold-acclimated insects were tested. Methoprene did not affect the cold tolerance of adults or larvae, regardless of cold acclimation. As seen in other studies, methoprene was not toxic to adults even at 66.6 ppm, but it was highly toxic to larvae (LD50 0.015 to 0.020 ppm). Cold tolerance was slightly greater in both adults and larvae, after being held at 15 °C for two weeks. This is the first study to report that a Juvenile Hormone analogue has an impact on insect heat tolerance.