The Role of Alternative Host-Plant Species in the Life of a Polyphagous Moth, Operophtera brumata (Lepidoptera: Geometridae)

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Abstract
As a major determinant of larval winter moth population levels is known to be the degree of synchrony between larval eclosion and the bud burst of the primary host-plant, the oak [Quercus], it is argued that 2 hitherto unstudied factors have a considerable effect on the insects'' population dynamics. These are: the events occurring immediately after eclosion and the effect of the period of food deprivation which occurs should no food be available locally; and the degree to which larvae can utilize food-plant species other than the primary host. The 1st instar larvae can discriminate between host-plant species. This is unaffected by the degree of food deprivation relevant to field conditions. Early deprivation has little if any adverse affects on the subsequent growth and development of larvae, and it may confer mild advantages. A comparison is made of the development of larvae reared on primary and alternative hosts [Crataegus, Malus, Prunus, Corylus and Fagus] before, during and after the period of peak level eclosion and oak bud burst in the field. Four of the 5 alternative host tested support satisfactory larval growth. It is only during the period of maximum oak bud burst that an oak diet results in a considerably greater reproductive success than that supported by a diet of alternative hosts. The polyphagy of winter moth larvae is a mechanism which promotes synchrony of larval eclosion with the primary host plant. It is also associated with several unusual features of winter moth biology; in particular the larval, as opposed to adult host selection and dispersal, as well as increased adult fecundity.

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