Thermoregulatory response of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) to infection by Beauveria bassiana, and its effect on survivorship and reproductive success.

Behavioral thermoregulation is a defensive strategy employed by some insects to counter infections by parasites and pathogens. Most reported examples of this type of thermoregulatory response involve behavioral fevering. However depending upon the life history of a host-insect and that of the parasite or pathogen, the host may respond by cold-seeking behavior. Thermoregulation is not only ecologically important; it may affect the success of parasites and pathogens as biological control agents. We examined if Frankliniella occidentalis (Pergande) thermoregulates in response to infection by Beauveria bassiana, a fungal pathogen commonly used for biological control. Fungal-infected thrips preferentially moved to cooler areas (12 °C) while healthy thrips sought out warmer temperatures (24 °C). This cold-seeking behavior suppressed the growth of B. bassiana in infected thrips, and significantly improved survivorship of infected thrips. At 24 °C, males only survived up to 10 d after infection and females up to 20 d after infection, which was substantially poorer survivorship than that of corresponding healthy individuals. However, individuals of both sexes survived up to 48 d after infection at 12 °C, which was a much less severe reduction in survivorship compared with the effect of B. bassiana infection at 24 °C. The proportion of females among progeny from infected thrips at 12 °C was higher than at 24 °C. Therefore, cold-seeking behavior is beneficial to F. occidentalis when infected by B. bassiana, and its effects should be considered in the use of B. bassiana in biological control programs.