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Abstract
Sirex noctilio F. is an invasive woodwasp native to Europe which has invaded countries in the Southern Hemisphere causing extensive damage to pine (Pinus spp.) stands. Its recent introduction into North America has generated concern for pine plantations in the southern United States. Ibalia leucospoides ensiger Norton (Hymenoptera: Ibaliidae) parasitizes the eggs and first instars of S. noctilio, and is considered one of its most effective biocontrol agents. My two research objectives were to: 1) identify and quantify the antennal sensillum of male and female I. l. ensiger; and 2) identify compounds that are attractive to I. l. ensiger. Antennae of I l. ensiger are sexually dimorphic, although there were no differences in the number of sensillum between sexes. Seven types of chemo- and mechano-receptors were identified on the antennae with varying numbers. In the laboratory, Ibalia l. ensiger showed oviposition responses to phytotoxic venom of Sirex spp. injected into logs and their hosts oviposition holes. Using GC-EAD, 14 compounds from Sirex venom and oviposition holes were found to be electrophysiologically active with I. l. ensiger antenna.