Mortality modeling of adult Tribolium confusum (Jacquelin du Val) exposed to different concentrations of carbon dioxide in a mixture with nitrogen

The effects of carbon dioxide (CO₂) gas in combinations with nitrogen (N₂) gas and temperature on the mortality of adult Tribolium confusum (Jacquelin du Val) were investigated at temperature levels of 20 °C, 25 °C, and 30 °C and CO₂ gas concentration levels of 0%, 40%, 50%, 60%, and 80% (v/v). Soon after exposing the insects to the undesirable atmospheric conditions, the insects sank into a state of coma and died if they were not returned to a normal atmosphere within an appropriate time estimated from the Weibull model. The ratio of motionlessness and mortality of insects depended strongly on the exposure time and temperature; however, there was also a slight dependence on the gas concentration. Mortality increased with exposure time and temperature. Six models were fitted to the insect mortality data, and a Weibull model gave the best fitting results, with a mean root mean square error of 0.1240. By using the Weibull model, the times required for 50% and 90% mortality of the insects were also estimated. The percent mortality increased rapidly with increasing temperature with 60% CO₂. The required time for 90% mortality at 20 °C was three times longer than that at 30 °C. In order to relate the percent mortality and temperature or CO₂ gas concentration a corrected time function model was employed. As a result of this fitting, death can be seen as a chemical process with the rate at which mortality occurs in a population being analogous to the rate of a chemical reaction. By comparing the mortality under non-zero oxygen concentrations with that under zero oxygen concentrations, the insects were killed easily under zero conditions.