Role of heat shock proteins during thermal stress in the milkweed bug, Oncopeltus fasciatus

As temperatures decrease in the fall, northern populations of the large milkweed bug, Oncopeltus fasciatu,s migrate south and reproduce, while subsequent generations recolonize habitat in the following spring and summer. Thus, a single breeding population of O. fasciatus is likely to experience a wide range of temperatures across its geographic range. In this study, we examined the thermal tolerance of O. fasciatus and measured expression levels of three heat shock proteins (Hsps) in response to thermal stress. O. fasciatus exhibited high tolerance to heat stress, as 87.5±6.3% survived a 90 minute exposure to 42°C. Meanwhile, only 37.5±11.1% survived a 3 h exposure to -10°C, a temperature well above its supercooling point. However, as demonstrated previously, O. fasciatus is capable of rapid cold-hardening (RCH), as a 1 h exposure to 0°C prior to 3 h at -10°C resulted in 85.0±2.9% survival. We isolated and cloned fragments from three O. fasciatus Hsps, Hsp90, Hsp70, and a small Hsp and measured gene expression using quantitative PCR following control (25°C), heat shock (90 minutes at 42°C), cold shock (3 h at -10°C), and RCH (1 h at 0°C). Preliminary results indicate strong upregulation of Hsp90 in response to heat shock and cold shock, and slight upregulation following RCH. Meanwhile, expression levels of Hsp70 are significantly increased in response to heat shock and RCH but unchanged by cold shock. Expression levels of the small Hsp have yet to be measured. Overall, these results suggest that Hsps in O. fasciatus are responsive to both heat and cold and may be involved in the RCH response.