Effects of cold stress during diapause on the survival and development ofDelia radicum (Diptera: Anthomyiidae) in England

Summary

Exposing diapausingDelia radicum (L.) to temperatures from-10.2 to-14.8° C during a 80-day experimental period reduced survival to eclosion and the rate of postdiapause development. No such effects occurred among those exposed to-7.1° C for up to 80 days. A continuous exposure to-10.2 or-14.8° C reduced survival of overwinteringD. radicum by the same amount as an equal duration of exposure to these temperatures interrupted by 14 days at 2° C, indicating that the effects of cold exposure were additive and that repair of cold-induced injuries did not occur at 2° C. The decreased survival with increasing duration of exposure to-10.2 or-14.8° C were described by the equations:

$$\begin{gathered} ln(p/1 - p) = 1.63 - 0.0204t_{ - 10.2} \hfill \\ ln(p/1 - p) = 1.03 - 0.519t_{ - 14.8} \hfill \\ \end{gathered} $$

Wherep=the proportion surviving to eclosion andt=the number of days of exposure to the temperature given by the subcript. An increased incidence of malformed adults was associated with low survival. Adult emergence occurred within two periods. Early-emerging flies required up to 230° D and late-emerging flies more than 330° D above 5.6° C. Among early-emerging flies, a reduced rate of postdiapause development was associated with low survival but the development of late-emerging flies was not affected.

OverwinteringD. radicum parasitized byTrybliographa rapae (Westw.) or byAleochara bilineata Gyll. responded similarly to unparasitizedD. radicum although those parasitized byT. rapae were less resistant to cold injury when exposed to-14.8° C.

D. radicum and its parasitoids are capable of surviving temperatures more severe than those normally occurring in England and Wales; and, therefore, cold injury is unlikely to affect their population dynamics.