Identity Of Hostseeking Chemicals

Some progress has been made in identifying chemicals important in host-seeking behavior of parasitoids. Volatiles involved in host habitat finding include ethanol and especially acetaldehyde produced in rotting peaches that attract the braconid, Biosteres longicaudatus, a parasitoid of tephritid fruit flies. Allyl isothiocyanate produced by crucifers is attractive to the braconid parasitoid of aphids D. rapae. The straight-chain hydrocarbons docosane, tricosane, tetracosane, and pentacosane from the scales of adult Helicoverpa zea moths are cues used by Trichogramma evanescens to locate host eggs. In the frass of H. zea, 13-methylhentriacontane is an examination-stimulating cue for the braconid parasitoid M. croceipes, as is heptanoic acid in the frass of the potato tuberworm (Phthorimaea operculella) for the braconid parasitoid, Orgilus lepidus. Members of a series of methyl branched hen-, do-, and tritriacontaines from the mandibular glands of Heliothis virescens serve to intensify searching of the braconid, C. nigriceps on areas of leaves damaged by host feeding. Long-chain hydrocarbons (heptacosane, nonacosane, and several dimethyl compounds) in the cuticle of gypsy moth pupae are important in the host acceptance behavior of the chalcid, Brachymeria intermedia. The ichnuemonid parasitoid I. conquisitor oviposits into a wax-covered cylinder of water mixed with the amino acids arginine, isoleucine, methionine, lysine, leucine, and serine, as well as magnesium chloride. The tachinid fly Cyzenis albincans lays very small, microtype eggs on oak foliage that caterpillars of the winter moth

(Operophtera brumata) eat. The parasitoid is stimulated to lay eggs in the presence of sugars exuded by damaged oak leaves, thus increasing the chance that its host will be nearby.

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