Elevated atmospheric CO₂ adversely affects a dung beetle's development: Another potential driver of decline in insect...

Insect declines have been attributed to several drivers such as habitat loss, climate change, invasive alien species and insecticides. However, in the global context, these effects remain patchy, whereas insect losses appear to be consistent worldwide. Increases in atmospheric CO₂ concentrations are known to have indirect effects on herbivorous insects, but the effects on other insects are largely unexplored. We wondered if elevated atmospheric CO₂ (eCO₂ ) could influence the growth and survival of insects, not via rising temperature, nor through their changes in food quality, but by other means. Rearing tunnelling dung beetle Euoniticellus intermedius (Reiche, 1848) at pre-industrial (250 parts per million [ppm]), current (400 ppm) and eCO₂ levels (600 and 800 ppm), we found that exposure to eCO₂ resulted in longer developmental times and increased mortality. Elevated CO₂ also caused reduction of adult size and mass which is detrimental to dung beetle fitness. Additional results showed associated increases in CO₂ levels inside dung brood balls, dung pH and respiration rates of the soil surrounding the developing dung beetles (CO₂ flux). We thus hypothesize that elevated CO₂ increases competition for O₂ and nutrients between soil microbiota and subterranean insects. Given that many insect orders spend at least part of their life underground, our findings indicate the possibility of a negative ubiquitous effect of eCO₂ on a large portion of the earth's insect biota. These findings therefore suggest an important area for future research on the soil community in the context of atmospheric change.