Acclimation for heat resistance in Trichogramma nr. brassicae: can it occur without costs?

Abstract 1. It is well known that animals can increase their stress resistance by prior exposure to sub‐lethal conditions, but this acclimation process is often accompanied by deleterious fitness effects. These may reflect a cost of acclimation, or more general costs arising from damage due to sub‐lethal exposures. 2. Acclimation for increased adult resistance to a 40 °C heat shock was tested in the egg parasitoid, Trichogramma nr. brassicae, following exposure of immature stages to 33 °C for different periods. Prepupal exposure did not increase heat resistance, but daily exposures at the pupal stage for 2 h day−1 and 3 h day−1 over 4 days increased survival of the shock. 3. Pre‐pupal exposure for 3 h day−1 over 4 days led to decreased parasitism reflecting general damage costs. Pupal exposure for 3 h day−1 and 4 h day−1 also decreased parasitism rates, but there were no deleterious effects when pupae were acclimated for 2 h day−1. 4. These findings indicate that acclimation can occur without costs in Trichogramma nr. brassicae and suggest a general phenotypic approach for separating acclimation costs from other fitness costs caused by sub‐lethal exposures. The potential for using acclimation to increase field parasitism success of this important group of parasitoids is discussed.