Temperature-dependent development of Xyleborus fornicatus (Coleoptera : Scolytidae), the shot-hole borer of tea in Sri Lanka: Implications for distribution and abundance

The effect of temperature on the rate of development of Xyleborus fornicatus (Eichh.) was determined by rearing individuals under a range of constant temperatures (15 -32 degrees C). Rates of development changed in a linear fashion over a wide range of temperatures. Estimates of lower development thresholds were obtained for eggs (15.7 +/- 0.50 degrees C), larvae (15.8 +/- 0.8 degrees C) and pupae (14.3 +/- 1.4 degrees C) and the degree days (DD) for development were 70 +/- 4.4, 95 +/- 8.5 and 72 +/- 5.1 DD, respectively. Optimum temperature for development was around 30 degrees C for all stages. Temperature fluctuation in cooler High Country areas (above 1400 m) with a mean temperature around 15 degrees C seems to be critical for the development of the pest, which may be responsible for the near absence of pest in those areas. Temperature fluctuations (18-30 degrees C) in the Mid Country region (600-1200 m) favor the development of the pest compared to development under constant conditions. The altitudinal distribution of the shot-hole borer across tea growing areas in Sri Lanka is, therefore, mainly governed by temperature