Phenology, polymorphism and insect-plant relationships of the larch budmoth, Zeiraphera diniana (Guenée) (Lepidoptera: Tortricidae), on alternative conifer hosts in Britain

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Abstract
Studies on populations of Z. diniana (Gn.) in Britain, where the tortricid has recently attained pest status, revealed differences in their structure and host-plant relationships when compared with populations at other European localities. A switch from the predominance of larch (Larix decidua) as a host in alpine Switzerland to pine (Pinus contorta) in upland Britain was governed by temperature which, during the egg stage, altered the phenological relationships between hatching caterpillars and foliage on the 2 conifers. Larvae which originated from populations on pine had higher survivorship on foliage of spruce (Picea) and larch than populations which originated on larch. Larval age heterogeneity, induced by a prolonged egg hatching period, was a marked feature of British populations and could have significant demographic consequences, including an occasional reduction in the degree of temporal separation of racial units at the adult stage. Patterns of polymorphism in larval samples from P. contorta and Larix spp. in a variety of forests in Britain gave support to a hypothesis of racial hybridization at the edge of the insect''s range. There were overall differences between color-type structure of larvae on larch at an English site and at a comparable Swiss locality, and also a similar trend in the change of a color-type index with changes in population density between years. Similar selective forces may apply to the population dynamics of Z. diniana throughout its range.