We examine the oviposition behavior of the parasitic fly Cyzenis albicans(Fall.) to determine if long-distance or contact chemical cues given off by damaged oak and apple foliage influences the attack of their host the winter moth Operophtera brumata(L.). Wind-tunnel experiments indicate the presence of an attractive odor in oak leaves and the absence of an attractant in apple leaves. The application of oak foliage extracts to apple trees increased the number of parasitoid eggs laid and the level of parasitism of winter moths in the field. The impact of altered host-seeking behavior by the parastoid is discussed in the context of the population ecology of its host.