Cold tolerance and diapause within and across trophic levels: Endoparasitic wasps and their fly host have similar phenotypes

Low temperatures associated with winter can limit the survival of organisms, especially ectotherms whose body temperature is similar to their environment. However, there is a gap in understanding how overwintering may vary among groups of species that interact closely, such as multiple parasitoid species that attack the same host insect. Here, we investigate cold tolerance and diapause phenotypes in three endoparasitoid wasps of the apple maggot fly Rhagoletis pomonella (Diptera: Tephritidae): Utetes canaliculatus , Diachasma alloeum , and Diac-hasmimorpha mellea (Hymenoptera: Braconidae). Using a combination of respirometry and eclosion tracking, we found that all three wasp species exhibited the same three diapause duration phenotypes as the fly host. Weak (short duration) diapause was rare, with <5 % of all three wasp species prematurely terminating diapause at 21 degrees C. Most D. mellea (93 %) entered a more intense (longer duration) diapause that did not terminate within 100 d at this warm temperature. The majority of U. canaliculatus (92 %) and D. alloeum (72 %) averted diapause (non-diapause) at 21 degrees C. There was limited interspecific variation in acute cold tolerance among the three wasp species: wasps and flies had similarly high survival (>87 %) following exposure to extreme low temperatures (-20 degrees C) as long as their body fluids did not freeze. The three wasp species also displayed little interspecific variation in survival following prolonged exposure to mild chilling of 8 or more weeks at 4 degrees C. Our study thus documents a remarkable conservation of cold tolerance and diapause phenotypes within and across trophic levels.

Automated summary

Low temperatures in winter can have a negative impact on the survival of organisms, particularly ectotherms. This study investigates the variation in overwintering strategies among groups of closely interacting parasitoid species. The researchers found that different species of endoparasitoid wasps exhibited similar diapause phenotypes as their host insect, the apple maggot fly. The study also reveals a high level of cold tolerance and consistency in survival rates among the three wasp species.