Estimating development and temperature thresholds of Scolothrips longicornis (Thysanoptera: Thripidae) on eggs of two-spotted spider mite using linear and nonlinear models

The development rate of the predatory thrips, Scolothrips longicornis Priesner, fed on Tetranychus urticae Koch was determined at 15, 20, 26, 30, 35, and 37A degrees C. No development occurred at 40A degrees C. The total development time from egg to adult emergence for females was estimated to be 48.1, 22.8, 13.6, 10.6, 8.3 and 9.6 days, respectively. The development time decreased with increasing temperature from 15 to 35A degrees C. In the temperature range of 15-37A degrees C, egg and larval mortality varied between 10% and 48% and 1.92% and 11.1%, respectively. The sex-ratio of S. longicornis was in favor of females at all tested temperatures and remained uninfluenced by temperature in the range of 15-35A degrees C with an average of about 75% females. The lower temperature threshold for the entire development period and the thermal constant for female S. longicornis using the common linear model were estimated to be 11.1A degrees C and 200 degree-days (DD), and 10.8A degrees C and 204 DD using the Ikemoto and Takai model. Data were fitted to four nonlinear development rate models and the thermal thresholds (T (min) and T (max)) and optimal temperature (T (opt)) estimated. The Briere-1, Briere-2, and Ikemoto and Takai linear models provided adequate descriptions of temperature-dependent development of S. longicornis. The upper temperature threshold was estimated to be about 42A degrees C. Temperature-dependent development data, thermal requirements and temperature thresholds can be used to predict the occurrence, number of generations and population dynamics of S. longicornis, an important biocontrol agent of T. urticae.