THE INFLUENCE OF TEMPERATURE ON EGG MORTALITY IN THE BUDMOTH ZEIRAPHERA-DINIANA (LEPIDOPTERA, TORTRICIDAE), AND ITS ROLE IN DETERMINING THEREGIONAL ABUNDANCE OF AN IMPORTANT FOREST PEST

The range of the moth Zeiraphera diniana Guenee and the regions where high population densities are infrequent and unpredictable are thought to be determined by high temperatures during egg pre-diapause. Exposu re of eggs to incubation temperatures known to be optimal for Z. dinia na elsewhere resulted in a pre-diapause mortality of 13% which corresp onds to known rates of egg mortality in British forests. Evidence sugg ests that high temperature and its duration are both important determi nants of pre-diapause egg mortality which, if experienced in forest co nditions, may prevent populations from reaching outbreak levels. Histo rical records of outbreaks were associated with lower than average Aug ust temperature. However, high temperatures on their own are unlikely to determine the range of the insect in Britain since a high proportio n of eggs survives extremes; more than 70% of British eggs survived 24 h exposure to a temperature of 30 degrees C. Variations in egg mortal ity among families of moths suggests a genetic basis for differences i n thermal tolerance. Furthermore, there may be selection for thermally -tolerant eggs in British forest environments and this could be connec ted with other forms of genetic differentiation in budmoth populations .