Journal of Insect Behavior, Vol. 6, No. 5, 1993 Role of Plant Volatiles in Host Location by the Specialist Parasitoid Microplitis croceipes Cresson (Braconidae: Hymenoptera) Philip J. McCall, 1,3 Ted C. J. Turlings, 1 W. Joe Lewis, z and James H. Tumlinson 1'4 Accepted January 14, 1993; revised February 6, 1993 A study was conducted to determine the primary source of volatile cues within the plant-host complex used by host-seeking free-flying female Microplitis cro- ceipes Cresson in flight tunnel bioassays. In single-source and two-choice tests, using wasps given an oviposition experience on either cotton (Gossypium hir- sutum) or cowpea (Vigna unguiculata) seedlings damaged by corn earworm (CEW; Helicoverpa zea Boddie), the damaged seedlings were significantly more attractive than the CEW frass, which was in turn more attractive than the larvae themselves. In a series of two-choice wind-tunnel tests, the discriminatory ability of the wasps was examined, following various oviposition experiences. Signifi- cantly more wasps flew to plants with "old" damage than to plants with ' 'fresh" damage, regardless of whether they had experience on fresh or old damage. In a comparison of plant species, wasps with only one experience on either host- damaged cotton or host-damaged cowpea were unable to distinguish between them, and showed no preference for either plant, whereas wasps with multiple experiences on a particular plant preferentially flew to that plant in the choice test. In comparing hosts with nonhosts, wasps successfully learned to distinguish CEW from beet armyworm (BAW; Spodoptera exigua) on cotton but were unable to distinguish CEW from either BAW or cabbage looper (Trichoplusia ni) on cowpea. The results show the important role played by plant volatiles in the location of hosts by M. croceipes and indicate the wasps' limitations in dis- l Insect Attractants, Behavior, and Basic Biology Research Laboratory, Agricultural Research Ser- vice, U.S. Department of Agriculture, P.O. Box 14565, Gainesville, Florida 32604. 2Insect Biology and Population Management Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, P.O. Box 748, Tifton, Georgia 31793. 3Present address: Biomedical Sciences Division, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, U.K. 4To whom correspondence should be addressed. 625 0892-7553/93/0900-0625507.00/0 9 1993 Plenum Publishing Corporation