Interactions of photoperiod and thermorhythm in the induction of larval diapause in the blowfly, Calliphora vicina R.-D. (Diptera: Calliphoridae)

Abstract

Laboratory experiments were conducted with a strain of Calliphora vicina originated from individuals collected in the environs of St. Petersburg, Russia. Females developed and were kept at 20° C under short day length of 12 h, their progeny developed at the same photoperiod but at different temperature regimes. At 12° C most of the larvae entered diapause, at 15° С about 50 % of the larvae diapaused, and at 18° C diapause was not observed. Thermorhythm (alternation of 12-h-long periods with temperatures of 12 and 18° C) induced diapause in approximately a third of individuals, regardless of whether the low temperature coincided with the dark or with the light phases of the photoperiod. Thus, the larval diapause of C. vicina represents an exception to the rule stating that the role of the night temperature in the diapause induction is much more important than that of the day temperature. The analysis of this and some other known exceptions to the above rule suggests that they can be expla ined by a combination of a very strong thermal and a very weak photoperiodic response which makes their interaction negligible.