Prey selection by a spider wasp, Batozonellus lacerticida (Hymenoptera: Pompilidae): Effects of seasonal variation in prey species, size and density

Abstract

AbstractPrey selection by a spider wasp, Batozonellus lacerticida, was investigated at the riverside of the Toyohira River in Misumai, Sapporo, Hokkaido over 7 years from 1981 to 1987. Seventeen species of araneid spiders were found in the study area and six of them were hunted by the wasps. Most (97.3%) of the 223 prey records obtained were of three species, Araneus macacus, A. marmoreus and A. pinguis. Nesting activity of the wasps continued until mid‐August in 1981, 1982 and 1986, but stopped in July in 1984, 1985 and 1987. The length of nesting period was related to whether the wasps successfully switched prey species from A. macacus to A. marmoreus and A. pinguis and A. pinguis or not Switching seemed to occur at the phase when density of A. macacus remained high, depending on the density of larger A. marmorus and A. pinguis. This switching had large effects on species composition and size distribution of actual prey. Chesson's index α calculated at every 10 day period revealed that the wasps preferred A. macacus to the two other species and large prey to medium and small ones. The effect of prey density on preference depended on whether A. macacus was present or absent. In the presence of it there were only slight differences in preference among various conditions of prey density. However, when A. macacus was absent, densities of both A. marmoreus and A. pinguis had some complementary effects on preference. The importance of prey size selection by pompilid wasps, and implications of density effects on preference are discussed.