The fitness of natural enemies should be altered in response to changes in herbivore quality induced by the impact of increased atmospheric CO2 levels on plants.We studied the effect of different CO2 levels on the aphid predator Episyrphus balteatus DeGeer fed either specialist or generalist aphids reared on either of two host plants under laboratory conditions. In the host plant that contains sinigrin (black mustard), elevated CO2 increased the sinigrin content of both host plant and the specialist aphid, but reduced the already very low levels in the generalist aphid. Predator development time increased with elevated CO2, while fecundity decreased. Consequently, individual fitness decreased slightly with increasing atmospheric CO2. Sinigrin significantly decreased fecundity and increased development time of the predator. As a result, fitness was significantly lower too. The consumption rate was influenced significantly by plant and prey solely and the interactions of host plant × prey type and CO2 level × prey type. Further research on the effects of climate change parameters (e.g. greenhouse gases such as CO2, ozone (O3) and nitrogen dioxide (NO2), etc.) separately and jointly under controlled environmental conditions will help to understand the nature and direction of their effects on natural enemies as part of the tritrophic system.

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