Bioclimatic analyses of Trichomalus perfectus and Mesopolobus morys (Hymenoptera: Pteromalidae) distributions, two potential biological control agents of the cabbage seedpod weevil in North America

Climatic requirements of natural enemies have important implications for predicting the outcome of classical biological control programs. A five year study (2011–2015) investigated the ectoparasitoid community of the oilseed rape pest Ceutorhynchus obstrictus (Coleoptera: Curculionidae), in different climate zones across Europe to better understand the distribution, abundance, phenology and thermal requirements of Trichomalus perfectus and Mesopolobus morys (Hymenoptera: Pteromalidae). Data generated were then used to develop bioclimatic models to predict the suitability and potential distribution of each species if introduced into North America for biological control of C. obstrictus. Findings indicated that, although T. perfectus and M. morys occupy the same feeding niche and overlap temporally, there are clear geographic differences in abundance. Trichomalus perfectus appears to be a ‘northern’ maritime species, whereas M. morys is likely a 'southern’, continental species. If introduced, it was predicted that both species would establish in canola growing regions of North America, although climatic conditions appear to be less favourable for T. perfectus than M. morys. This study showed that variation in regional distributions may occur and these are likely based on differing tolerance to climatic conditions. Understanding these tolerances can enhance precision of ecological niche models that predict potential distributions of parasitoids for introduction as candidate biological control agents. Furthermore, the work reported here provides a basis for future research to determine if climate change may favour species such as M. morys that are adapted to warmer summer conditions.