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

Abstract

The effects of elevated CO₂ (550 and 750 µL/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%) µL/L CO₂ compared to ambient CO₂, respectively. In addition, there was a significant decrease (10%) in the emergence rate of A. picipes under 750 µL/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%) µL/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.

Keywords:

• Harmonia axyridis
• Aphidius picipes
• Sitobion avenae
• spring wheat
• elevated CO₂
• open-top chamber

Acknowledgments

We thank Madam Ding Yu LEI, the Dean of the Beiai Science and Technology Center, Hebei Province of China, for her help in the field OTC experiments. This research was supported by the National Key Basic Research Project ‘973’ (2006CB102002), the Innovation Program of Chinese Academy of Science (KSCX2-YW-N-006), the National Natural Science Foundation of China (30571253), the Chinese Postdoctoral Foundation (2005038291) and the Exoteric-Application Foundation from the Stake Key Laboratory of Integrated Management of Pest Insects and Rodents (Chinese-IPM-0601).