Determining suitability of thermal development models to estimate temperature parameters for embryonic development of Sitona lepidus Gyll. (Coleoptera: Curculionidae)

The clover root weevil, Sitona lepidus Gyll. is a pest of clovers (Trifolium spp.), particularly white clover (T. repens). Larva feeding severely impairs the capacity of white clover to fix atmospheric nitrogen, by attacking the nitrogen-fixing root nodules. Development of the egg stage was studied at six different constant temperatures ranging from 9 to 30A degrees C to improve the basis for phenological forecasts. Development occurred over the entire range of temperatures, although hatching percentage at 30A degrees C was only 24.4% compared to 90.1% at 28.5A degrees C. Developmental time decreased with increase in temperature from 9 to 28.5A degrees C but increased markedly at 30A degrees C. At 28.5A degrees C, the embryo development period was the shortest (10.35 days); whereas at 9A degrees C, this parameter was the longest (55.08 days). Using linear regression, the lower threshold temperature was calculated 4.38A degrees C and the thermal constant was 236.45 degree-days. The relationship between constant temperature and developmental rate was evaluated using nine models. The suitability of the models was evaluated based on eight indicators (R (2), RSS, R (adj) (2) , AIC, BIC, AICC, W (j) , and Z (i) ). Of the nonlinear models, the Logan-6, Sharpe and DeMichele, and Lactin models were the most accurate at calculating t (opt) of 27, 27.50, and 28A degrees C, respectively. The results suggest that of the three models (Lactin, Briere, and Hilbert and Logan), that estimated critical temperatures, (t (min), t (opt), and t (max)), Lactin gave the most suitable fit of data. This response of S. lepidus to temperature can be used for developing phonological models to predict the timing of egg hatch which are important for management programs targeting the weevil.