Rapid cold hardening in the olive fruit fly Bactrocera oleae under laboratory and field conditions

Abstract A rapid cold hardening response was studied in females and males of the olive fruit fly Bactrocera (Dacus) oleae . When laboratory‐reared females and males were transferred and maintained from the rearing temperature of 24 °C for 2 h to −6.5 °C approximately 5% survived. However, conditioning of both females and males for 2 h at various temperatures from 0 to 10 °C before their exposure for 2 h to −6.5 °C increased survival to 80 to 92%. A similar rapid cold hardening response in both females and males was also induced through gradual cooling of the flies at a rate of approximately 0.4 °C per min. The rapid increase in cold tolerance after prior conditioning of the flies to low temperatures, was rapidly lost when they returned to a higher temperature of 24 °C. In the field, in late February and early March, females and males were capable of a rapid cold hardening response. After exposure to the critical temperature they suffered a high mortality when tested in the afternoon and low mortality early in the morning on consecutive days, probably because of differences in the prevailing field temperatures a few hours before testing. This plasticity of cold tolerance gained through rapid cold hardening may allow the flies to survive during periods of the year with great fluctuation in circadian temperatures.