Intraspecific variation in rapid cold hardening and acclimation of the adventive parrot’s feather weevil, Phytobius (=Parenthis) vestitus, in the southern USA

Plasticity in thermal tolerance, expressed through acclimation or rapid cold hardening, for example, provides organisms with a mechanism to deal with unexpected and often rapid changes in the thermal environment. Spatial variation in response to high or low temperatures may occur due to evolutionary adaptation, particularly if a fitness increase coincides with the ability to respond quickly to environmental change. Thermal tolerances of beneficial insects used for biological control dictate where and under what thermal conditions the insects will provide value to management programs. We investigated two aspects of thermal phenotypic plasticity in response to thermal conditions using four populations of the adventive parrot’s feather weevil, Phytobius vestitus, from the southern USA. At low temperatures, we determined the presence and variation in rapid cold hardening in two of the four populations using two temperature ramping rates. At high temperatures, all P. vestitus populations displayed a significant heat acclimation response, documented as elevated maximum critical and lethal temperatures after acclimation. The relationship between population mean thermal tolerance or plasticity and climate of the source population was not consistent. These results demonstrate the presence of geographic variation in phenotypic plasticity in response to thermal environments and provides an additional consideration for biological control programs for which understanding thermal limits of agents is a priority.