A COMPARISON OF THE COLD HARDINESS OF POPULATIONS OF DELIA-RADICUM (L) (DIPTERA, ANTHOMYIIDAE) FROM SOUTHERN ENGLAND AND THE CANADIAN PRAIRIES

The Canadian population of Delia radicum is more cold hard than the English population in that the supercooling point is slightly lower and overwintering pupae are less sensitive to lower temperatures and longer exposure times, but the Canadian population is slightly less cold hardy at higher temperatures within the cold injury zone. Females were more susceptible to cold-induced mortality than males among the Canadian population, but this sex difference was not significant in the English population. The bounds of the cold injury zone for species or populations of freezing susceptible, diapausing insects plus the sensitivity of the species to cold injury within this zone can provide an ecologically sound method of describing cold hardiness. -from Authors