The effect of concentrations of carbon dioxide (C02) that can be produced by biological respiration (7.5–19.2%) on oviposition of adultTribolium castaneum(Herbst),Cryptolestes pusillus(Schönherr), orC. ferrugineus(Stephens) was determined. Relative to controls,T. castaneum,C. pusillus, andC. ferrugineus, exposed to 7.5% CO2for 1 wk, had numbers of offspring reduced by 43, 94, and 50%, respectively, and the total population at 6 wk was reduced 53, 84, and 19%, respectively. With levels of ≥17.1%CO2for 1 wk, no offspring were produced and exposed adults had high mortality. Eggs and subsequent immatures ofTribolium confusumJ. du Val,T. castaneum, orC. ferrugineuswere exposed for 3 wk to elevated levels of CO2at 22°C. Insect development was similar at 7.5 and 8.6% CO2with mean mortality 43, 62, and 30% greater than controls forT. confusum,T. castaneum, andC. ferrugineus, respectively. Also, mean levels of 5.8–8.3% CO2for 7 wk reduced, on all sampling dates, populations ofT. confusumby 85%,T. castaneumby 99%,C. pusillusby 68%, andC. ferrugineusby 54%. AlthoughT. castaneumhad a greater oviposition rate than C. pusillus at 7.5% CO2, immature mortality was greater forT. castaneum. Based on long-term exposure to levels of CO2which can be produced by biological activity that affects oviposition and immature development, species in increasing order of sensitivity to CO2areC. ferrugineus,C. pusillus,T. confusum, andT. castaneum.