Host searching and oviposition by Leschenaultia exul, a tachinid parasitoid of the forest tent caterpillar, Malacosoma disstria

Leschenaultia exul is attracted to recent feeding damage or the herbivore-host plant complex preferentially on aspen poplar compared to balsam poplar trees (Mondor and Roland, 1997), however, on-plant behaviors by this fly are not known. Bess (1936) found that L. exul reared from eastern tent caterpillar, M. americanum larvae, oviposited on foliage when the ends of cherry leaves were clipped or when M. americanum larvae were placed within their rearing cage. Oviposition was attributed to the odor liberated by either the host or the host plant, although it was not experimentally determined to which of these the flies responded. The purpose of this study was to determine if aspen poplar and balsam poplar foliage with similar levels of defoliation would differ in their suitability to L. exul for both host-searching and oviposition. We also attempted to determine the stimulus leading to oviposition, which may, in turn, help both to predict and to explain parasitism rates of FTCs on different host tree species.