The impact of agricultural management on the parasitization of aphidophagous hoverflies (Diptera: Syrphidae)

Abstract

In 2007, a 3-year survey was started in northeastern Italy to assess the influence of agricultural management on parasitoid composition and parasitism rates of parasitoids attacking larvae and pupae of Syrphidae (Diptera). Two types of management were considered – intensive (including wheat and maize monoculture with very low or null vegetation diversity) and extensive (with different types of habitats, characterized by a higher vegetation complexity). In habitats simplified by intensive agriculture, and particularly in maize fields, parasitism rates of syrphid larvae were higher than recorded in more diversified habitats. A substantial difference in the composition of the parasitoid complex was also found. In extensive and wheat sites, Diplazontinae (Braconidae), highly specialized to Syrphidae, were the dominant parasitoids, whereas in maize fields Pachyneuron (Pteromalidae) species, known as generalists, accounted for more than 80% of total parasitoids. In the habitats where Pachyneuron spp. were dominant, parasitism rates were very high. Conversely, in habitats where Diplazontinae were more abundant, the parasitism rates were very low. The higher rate of parasitism of syrphid larvae and pupae recorded in intensive monocultures could have a large impact on the development and control of aphid populations in such crops.

Keywords:

• Hymenoptera parasitoids
• Diplazontinae
• Pachyneuron
• population dynamics

Acknowledgements

We are grateful to G.E. Rotheray for help with Diplazontinae identification, and R.R. Askew and J. Pujade-Villar for the identification of Pachyneuron and Figitidae specimens. G. Camerini kindly allowed us to study the specimens he reared in Pavia. Two anonymous reviewers provided valuable comments on an earlier draft of this manuscript.