The influence of temperature on egg mortality in the budmoth Zeiraphera diniana (Lepidoptera: Tortricidae), and its role in determining the regional abundance of an important forest pest

Abstract

AbstractThe range of the moth Zeiraphera diniana Guénée and the regions where high population densities are infrequent and unpredictable are thought to be determined by high temperatures during egg pre-diapause. Exposure of eggs to incubation temperatures known to be optimal for Z. diniana elsewhere resulted in a pre-diapause mortality of 13% which corresponds to known rates of egg mortality in British forests. Evidence suggests that high temperature and its duration are both important determinants of pre-diapause egg mortality which, if experienced in forest conditions, may prevent populations from reaching outbreak levels. Historical records of outbreaks were associated with lower than average August temperature. However, high temperatures on their own are unlikely to determine the range of the insect in Britain since a high proportion of eggs survives extremes; more than 70% of British eggs survived 24 h exposure to a temperature of 30°C. Variations in egg mortality among families of moths suggests a genetic basis for differences in thermal tolerance. Furthermore, there may be selection for thermally-tolerant eggs in British forest environments and this could be connected with other forms of genetic differentiation in budmoth populations.