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Influence of agricultural landscape structure on parasitoid abundance: a longer-term perspective.
Menalled, Fabian1, Costamagna, Alejandro2, Marino, Paul3, Landis, Douglas2, 1 2 3
ABSTRACT- This study assessed long-term temporal variations in the relationship between agricultural landscape complexity and parasitoid abundance and diversity in Ingham County, Michigan. The study site consisted of a complex and a simplified agricultural landscape separated by a transition zone. Landscape structure was quantified using black and white aerial photographs and digital land-use data. A highly heterogeneous mixture of crop and non-crop habitats characterized the complex landscape, while the simple landscape contained little non-crop habitats. Fields in the complex landscape were 75% smaller, had 63% more perimeter of wooded field edge per hectare of field area, and had 81% more field edge in wide hedgerow than those in the simple landscape. Between June and July 1994, 1996, 1998, and 2000, 13,626 Pseudaletia unipuncta larvae were released into maize fields. A total of 3,221 larvae were recovered and reared in the laboratory with 917 individuals parasitized by 15 species of parasitoids. Two species, Glyptapanteles militaris and Meteorus communis, represented 94.5% of the parasitoids recovered. Agricultural landscape structure influenced the temporal of P. unipuncta parasitism. While G. militaris was sampled in the simple (53.7% of total recovery) and complex landscape (46.3%), M. communis was the mostly found in the complex landscape (89.7%). Year to year fluctuations in percent parasitism were greater in the simple than in the complex landscape.
KEY WORDS: agroecosystems, conservation biological control, parasitoids, landscape complexity