Impacts of elevated CO2 on Bemisia tabaci infesting Bt cotton and its parasitoid Encarsia formosa

Atmospheric carbon dioxide concentration is expected to rise in the coming decades. Rising atmospheric CO2 levels may alter plant-insect-parasitoid associations due to the indirect effects of CO2 enrichment on phytochemicals important for herbivore and parasitoid nutrition. Tritrophic effects of elevated CO2 on Bt cotton (GK-12) and non-transgenic (Simian-3, or S3) cotton [Gossypium hirsutum L. (Malvaceae)], Bemisia tabaci (Gennadius) biotype B (Hemiptera: Aleyrodidae), and its parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae), were examined in open-top chambers. Significantly, longer egg-adult developmental duration and higher mortality of nymphs were observed under elevated CO2 concentrations on both cotton cultivars during three successive generations. However, no significant differences were found in adult longevity, offspring sex ratio, and the number of eggs laid per female adult of B. tabaci fed on transgenic (GK-12) or non-transgenic cotton (S3) grown under elevated CO2. Abundance of B. tabaci adults increased from 10 to 120 per plant and then decreased to 40 per plant through the growing season, but no significant differences in density occurred between CO2 treatments and between cultivar treatments. Similarly, no significant differences were found in the developmental duration, parasitization rate, and adult emergence rate of E. formosa after parasitizing B. tabaci for three successive generations. Our results showed that the effects of transgenic Bt cotton did not significantly affect the development, survivorship, life span, or fecundity of B. tabaci and its parasitoids. Moreover, interactions between B. tabaci and E. formosa were not significantly affected by elevated CO2. These results suggest that the biological control of B. tabaci by E. formosa would not be influenced by transgenic Bt cotton and/or elevated CO2, indicating that the current risk management strategy regarding B. tabaci outbreaks and biocontrol by E. formosa will remain effective if the atmospheric CO2 level continues to rise.