Effect of elevated CO2 on the population development of the invasive species Frankliniella occidentalis and native species Thrips hawaiiensis and activities of their detoxifying enzymes

Increased atmospheric CO2 concentrations may directly affect insect behavior and physiology. Native and invasive insects may have different levels of adaptability to elevated CO2. The invasive species Frankliniella occidentalis and the native species Thrips hawaiiensis are economically important pests. We determined the effects of elevated CO2 on these pests by monitoring their development, survival, and oviposition under different CO2 concentrations (400, 600, and 800 mu l L-1). We also determined detoxifying enzyme activities in larvae and adults. Frankliniella occidentalis and T. hawaiiensis showed faster development but lower survival rates as the CO2 concentration increased. Fecundity significantly increased in F. occidentalis but decreased in T. hawaiiensis with increasing CO2 concentrations. The net reproductive rate (R-0) and intrinsic rate of increase (r(m)) were highest in F. occidentalis and lowest in T. hawaiiensis in the highest CO2 treatment. At each CO2 concentration, compared with T. hawaiiensis, F. occidentalis developed faster and had higher survival rate, fecundity, R-0, and r(m). The activities of detoxifying enzymes, except for acetylcholinesterase activity in second instars, increased in both species with increasing CO2 concentrations. Carboxylesterase and glutathione S-transferase activities were always higher in F. occidentalis than in T. hawaiiensis. At each CO2 concentration, carboxylesterase and acetylcholinesterase activities were higher in adults, but glutathione S-transferase activities were higher in larvae, indicative of different physiological responses between adults and larvae. In summary, elevated CO2 benefited the population development of F. occidentalis but negatively affected that of T. hawaiiensis. This may be related to the activities of detoxifying enzymes.