Impact of elevated CO2 on the third trophic level:: A predator Harmonia axyridis and a parasitoid Aphidius picipes

The effects of elevated CO2 (550 and 750 mL/L vs. ambient CO2) on the third trophic level, a predator Harmonia axyridis (Pallas) and a parasitoid Aphidius picipes (Nees), were studied in open-top chambers. The impact of elevated CO2 on the growth and development of H. axyridis was either weak or nonexistent, whereas the abundance of the parasitized aphid (Sitobion avenae Fabricius) by A. picipes showed a significant increase in 550 (12.5%) and 750 (19.6%) mL/L CO2 compared to ambient CO2, respectively. In addition, there was a significant decrease (10%) in the emergence rate of A. picipes under 750 mL/L CO2 compared to ambient CO2 (P < 0.05). The predator and the parasitoid both substantially suppressed aphid abundance, especially in elevated CO2 for A. picipes. Moreover, H. axyridis and A. picipes preferred to prey on/ parasitize more aphids, S. avenae, infested on 550 (9.1 and 16.9%) and 750 ( 23 and 25.7%) mL/ L CO2-grown wheat plants than those fed ambient CO2-grown wheat plants. These initial results indicate that elevated CO2 markedly changes the predation/ parasitization preference by the predator/ parasitoid for wheat aphids. The biocontrol efficiency of A. picipes against S. avenae can be enhanced in elevated CO2; simultaneously, elevated CO2 has adverse effects on the growth and development of A. picipes-parasitized S. avenae.