Host patch size effects have been investigated in regard to specific host-parasitoid systems (population level response) but no studies have investigated effects on the diversity of parasitoids recovered (community level response). In addition, no studies have focused on the response of parasitism to interactions between landscape structure and host density. This study addresses the effect of host density at both population and community levels in landscapes with differential structural complexity. The study site consists of a complex and a simplified agricultural landscape separated by a transition zone, in Ingham County, Michigan. The complex landscape is composed of a highly heterogeneous mixture of crop and non-crop habitats, while the simple landscape contains little non-crop habitats. Previous studies using a low density of sentinel larvae of the armyworm Pseudaletia unipuncta found 9 parasitoid species in the simple landscape and 12 species in the complex landscape. Two species, Glyptapanteles militaris and Meteorus communis, represented 94.2% of the parasitoids recovered. While G. militaris was almost equally sampled in the simple and complex landscape, M. communis was found mostly in the complex landscape. Year to year fluctuations in percent parasitism were greater in the simple landscape than in the complex landscape. In this study, armyworm larvae were release in three cornfields per landscape at a rate of one (low-density) or three (high-density) larvae per plant, for a total of 12,960 larvae. The following hypotheses were tested: 1) patches with higher host density have increased parasitism; 2) patches with increased host density attract more species of parasitoids; 3) patches with increased host density attract more species of parasitoids in complex than in simple landscapes (landscape by density interaction).
Species 1: Lepidoptera Noctuidae Pseudaletia unipuncta (armyworm)
Species 2: Hymenoptera Braconidae Glyptapanteles militaris
Species 3: Hymenoptera Braconidae Meteorus communis
Keywords: landscape structure, parasitoids
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA