EFFECTS OF TEMPERATURE ON GROWTH, DEVELOPMENT AND DIAPAUSE IN THE YELLOW DUNG FLY - AGAINST ALL THE RULES

The effects of rearing temperature (and photoperiod) on growth, develo pment. body size, and diapause induction and termination in the yellow dung fly, Scathophaga stercoraria, were investigated by allowing repl icate families of larvae to develop in the field along a time sequence approaching the onset of winter. This was supplemented with extensive laboratory rearing. At constant laboratory temperatures, growth rates were maximal between 15 degrees C and 20 degrees C and decreased at h igher (25 degrees C) and Iower (10 degrees C) temperatures, while the development rate was maximal at 15 degrees C. Perhaps related to this. yellow dung flies reached a given size faster at naturally variable, as opposed to constant. temperatures. In the field, lower temperatures towards the end of the season resulted in larger individuals that gre w faster. Adult body size increased as development time, expressed in calendar days, increased, a positive relationship commonly taken for g ranted in life history theory, but decreased as development time expre ssed in degree-days increased. The effect of temperature oil growth, d evelopment and body size fall thus change or even reverse if individua ls can alter their growth rate independently of development time, and if the physiological effects of temperature are factored out by conver ting development time into degree-days above a lower development thres hold. Therefore, supposedly well-established trends possibly need to b e re-examined along these lines. Pupal winter diapause towards the end of the season was highly reversible by temperature. Pre- and post-win ter emergence patterns together suggest that the minimum time for yell ow dung flies to successfully complete development. at any time of the year, is about 230-250 degree-days.