Niche Relations of Predatory Stinkbugs (Podisus spp., Pentatomidae) Attacking Tent Caterpillars (Malacosoma americanum, Lasiocampidae)

Abstract

Colonies of the eastern tent caterpillar (Malacosoma americantnm, Lasiocampidae) and nearly 700 associated adults of the predatory stinkbugs Podisus maculiventris, P. placidus, P. modestus and P. serieventris (Hemiptera: Pentatomidae) were censused in 1977-1979 near Ithaca, New York. Most observations were made in an old field where three of the four pentatomid species (all but P. serieventris) occurred and attacked the tent caterpillars. While differences in seasonal timing occurred among the three stinkbug species in the old field, they were found together at tents each sprihg midway through the larval development of M. americanum. During this period of seasonal overlap, the three species displayed similar patterns of activity and sought out prey of similar size on the same trees. The three predators differed, however, in their locations on individual trees: P. placidus occurred most often inside tents, P. maculiventris on or within 30 cm of tents, and P. modestus more than 30 cm distant from the nearest tent. Because individual predators readily attack prey already subdued by other individuals, this divergence in hunting sites reduced interspecific interference in consumption of prey. INTRODUCTION In eastern North America, four predatory stinkbugs of the genus Podisus (Hemiptera: Pentatomidae) prey upon colonial larvae of Lepidoptera and Hymenoptera (sawflies) which defoliate trees and shrubs. Various combinations of the four species have been reported attacking different species of prey (e.g., Kirkland, 1898; Sullivan and Green, 1950; Coppel and Jones, 1962; Tostowaryk, 1971; Morris, 1972). The shifting composition of this association of predators from place to place and time to time suggests that the association is an unstructured assemblage of species, each with its own independent habits. Among the sites frequented each spring by adults of these predators are tents of the eastern tent caterpillar Malacosoma americanum (Fabricius) (Lasiocampidae). I undertook the following study of stinkbugs attacking tent caterpillars to examine whether this association of predators is indeed as unstructured as casual observation suggests. I address two central questions: (1) do the predators differ in their use of a common prey? and (2) do such differences result from independent adaptation to exploit the prey, or from competitive interactions among predators? STUDY SITES AND METHODS Obserations were made during the springs of 1977-79 at three sites near Ithaca, N.Y. Most observations were made in an old field in an advanced state of secondary succession at Whipple Farm Research Area of Cornell University. Tent caterpillars heavily infested black cherries (Prunus serotina Ehrh.) and apples (Malus sylvestris Mill.), and individual trees often bore several tents. Additional observations were made in a mixed forest stand dominated by hemlock (Tsuga canadensis (L.) Carr.), and in a deciduous woods dominated by oaks (Quercus spp.) and hickories (Carya spp.). Tent caterpillars inhabited black cherries in these two sites. Trees infested with tent caterpillars weLe visited and searched for stinkbugs every few days in the old field in 1977-1979 and in the wooded sites in 1977. These wooded 1 Present address: Division of Biology, Kansas State University, Manhattan 66506.