Response of Trichogramma brassicae (Hym.: Trichogrammatidae) to temperature: Utilizing thermodynamic models to describe curvilinear development

Temperature has profound effects on biological efficiency of parasitoid wasps. In the present study, effects of seven constant temperatures (12, 15, 20, 25, 30, 32 and 35 +/- 0.5 degrees C) on the pre-adult development of Trichogramma brassicae (Hymenoptera: Trichogrammatidae) were investigated on Sitotroga cerealella (Lepidoptera: Gelechiidae). Temperature effects on the emergence rate and sex ratio were also determined. The development rate of T. brassicae was described using two linear and twenty non-linear functions and critical bioclimatic temperatures (i.e., T-min, T-opt, T-max and k) were estimated. Efficiency of models was assessed by different criteria (i.e., R-2, R-adj(2), SSE, AIC, AICc, BIC and zi). Rate of development increased from 12 to 30 degrees C but decreased at two higher temperatures (i.e., 32 and 35 degrees C). At all thermal regimes a higher number of female individuals was emerged than males (1.81, 2.23, 2.03, 1.44, 1.78 and 1.78 female: male, respectively). At 12 degrees C, the lowest rate of parasitoid emergence (9%) was observed. The lower threshold predicted by the two linear models were 8.13 (Ordinary regression method) and 8.36 degrees C (Ikemoto method). These models predicted the thermal constant for pre-adult development as 181 and 177 DD, respectively. The estimates of optimum temperature ranged from 30 to 32 degrees C with an upper threshold between 36 and 41 degrees C, depending on which model was used. Based on both biological and statistical goodness-of-fit criteria, the non-linear model of Lactin-1 had the best described the experimental data. The information herein highlighted the higher performance of T. brassicae at tropical conditions and can be helpful to predict possible effects of temperature on developmental rate, select the best period of time for inundative release and improve mass rearing protocols of this parasitoid wasp.

Automated summary

The study revealed significant effects of temperature on the biological efficiency and development rate of parasitoid wasps, with the optimum temperature range being 12 to 30 degrees Celsius. Female individuals emerged more than males under all temperature regimes, with a decrease in development rate observed at two higher temperatures (32 and 35 degrees Celsius).