There is a review concerning the effects of carbon dioxide on insects in: Annual Review of Entomology, 1989, 34, 97-116 Paragraph concerning mortality pp 107-108. Insects are in fact very resistant to CO2 With regard to bees, A. Deyme (in Apidologie, 1977, 8 (3), 217-228) tested different concentrations of CO2 (to 75%) on bees of different ages. No bees died and the 2-day-old bees were the most sensitive .