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℃）. 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±0.5℃）, larvae （15.8±0.8℃） and pupae （14.3±1.4℃） 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~C for all stages. Temperature fluctuation in cooler High Country areas （above 1400 m） with a mean temperature around 15℃ 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℃） 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.

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°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±0.5°C), larvae (15.8±0.8°C) and pupae (14.3±1.4°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°C for all stages. Temperature fluctuation in cooler High Country areas (above 1400 m) with a mean temperature around 15°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°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.