Lymantria monacha (L.) (Lepidoptera: Lymantriidae) is a Eurasian pest of conifers that has potential for accidental introduction into North America. The phenology over the entire life cycle for L. monacha individuals from the Czech Republic was compared on Picea glauca (Moench) Voss (white spruce) and a newly developed artiÞcial diet. Individuals reared on the artiÞcial diet had lower larval mortality, slightly higher pupal mortality, developed faster, the majority of females went through one

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... ss instar, and adults weighed slightly more than those reared on the spruce foliage. Individuals reared on the spruce foliage survived and developed at rates similar to those documented in previous studies on preferred hosts. The host-free rearing methods and artiÞcial diet presented here will allow L. monacha to be mass reared year round to aid in the advance of bioassay-based research aimed at preventing introductions and eradicating this pest if it should become established in parts of the world outside its native range. The phenology documented here suggests that managers can expect the timing of peak second instars for L. monacha to occur later than that for gypsy moths, Lymantria dispar (L.), and the timing of male ßight to occur earlier than that of gypsy moth, if both species hatch at the same time and develop under the same environmental conditions.