HOST FINDING BEHAVIOR OF COELOIDES BRUNNERI (HYMENOPTERA: BRACONIDAE)

Abstract

The host-finding search patterns of Coeloides brunneri Viereck, a braconid parasite of Douglas-fir beetle larvae, were studied by visual observations and from tracings of the parasite’s path on a plastic cylinder wrapped around a beetle-infested log on which the parasite was searching. The female parasite locates its host, lying under approximately.6 cm of bark, through four distinct phases of host finding: random search, nonrandom search, oviposition, and nonsearch (resting and cleaning). Random search is characterized by large areas of bark being examined in a relatively straight path. Nonrandom search is a highly intensified examination of a small bark area and numerous turns of greater than 70°. Nonrandom search is initiated only at the end of a bark beetle gallery. Ovipositional probes are the culmination of successful host finding, in which the parasite paralyzes the host and deposits an egg. C. brunneri searched effectively on both Dendroctonus pseudotsugae Hopkins in Douglas-fir and D. ponderosae Hopkins in ponderosa pine, although there was a slightly more efficient search on D. pseudotsugae. The percentage of time spent in each search pattern was identical in 90-minute and 24-hour tests. A stimulus associated with the end of a larval gallery was concluded to be the key stimulus by which the parasite recognizes its host. Amputation experiments showed that the antennae are the principal receptor organs used in host finding. Various experiments and observations produced no evidence that sound or vibrations produced by the host, sound produced by the parasite (sonar), magnetism or odor of the host, or its host tree are used in host finding.