Comparison on mortality, pupation, and emergence of Plodia interpunctella (hübner) treated by 2, 4, 6, and 8% carbon dioxide mixed with 2 and 4% oxygen at three temperatures

Low concentration CO2 (e.g., 2–8%) mixed with 2–4% O2 balanced by N2 is more economically feasible than applying 99.99% N2 alone. Mortality, pupation, and emergence of the fifth instar larvae of Plodia interpunctella (Lepidoptera: Pyralidae) were tested in 2 or 4% O2 mixed with 2, 4, 6, or 8% CO2 balanced by N2 at 28, 23, and 18 °C. Mortality of eggs, second instar larvae, and pupae was tested in the mixture of 2% O2, 4% CO2, and 94% N2 at the three temperatures. When fifth instar larvae were exposed in 2% O2 mixed with 0, 2, 4, 6, and 8% CO2 or increasing temperature, the LT50, LT99 value, and time reaching 100% mortality was decreased significantly. Exposing in 4% O2 mixed with 0, 2, 4, 6, and 8% CO2, the pupation and emergence of the surviving fifth instar larvae were also decreased significantly, and reduced more in higher temperatures. This study found 2, 4, 6, and 8% CO2 had additive effect to low O2 on insect mortality, pupation, and emergence at any tested temperature, and higher CO2 concentration or temperature resulted in a higher additive percentage. The fifth instar was the most tolerant stage to the gas mixtures followed by second instar larvae, pupae, and egg; and increasing temperature would sufficiently decrease the lethal exposure time.