Synergistic effect of carbon monoxide mixed with carbon dioxide in air on mortality of stored-grain insects

Rusty grain beetle, Cryptolestes ferrugineus (Stephens), red flour beetle, Tribolium castaneum (Herbst), and granary weevil, Sitophilus granarius (L.), are dominant stored-grain pest species in Canada. A study to determine the effect of carbon monoxide (CO) mixed with carbon dioxide (CO₂) in air on controlling stored-grain insects was conducted in the laboratory. Within modified airtight gas exposure systems, mixed-age adults of rusty grain beetle, red flour beetle, and granary weevil in tough wheat with moisture content of 15% were exposed for 48, 96, 144 and 192 h to three types of gas mixtures in air, 5% CO, 30% CO₂, and 5% CO +30% CO₂ at 20°C and 30°C, the balance of the gases being air.;Carbon monoxide alone had no effect on mortality of the three insect adults. For C. ferrugineus, there was no difference in mortality between by CO₂ alone and CO₂ + CO mixture at either temperature for all exposures. However, both T. castaneum and S. granarius had higher mortality in the CO₂ + CO mixture than the CO₂ alone at both temperatures. Moreover, S. granarius was more susceptible to CO₂ + CO mixture than T. castaneum. These results suggest that for certain species CO could be used to increase the efficiency of CO₂, especially at high temperature. Inhibition by CO to electron transport chain at the cellular level is presumed to exert synergistic influence on inducing greater mortality of some insects under CO₂ stress.