PHENOTYPIC VARIATION IN COLOR PATTERN AND SEASONAL PLASTICITY IN ERISTALIS HOVERFLIES (DIPTERA, SYRPHIDAE)

1. An examination of phenotypic variation in colour pattern was carried out on four Eristalis hoverfly species using museum material. 2. The amount of phenotypic variation varied substantially among the species with E.arbustorum being the most variable. The other species showed a wide colour pattern range but less variation within that range (E.abusivus and E.nemorum), or a narrow range of colour variation (E.horticola). 3. Sexual colour dimorphism was apparent in all four species, but most pronounced in E.abusivus and E.nemorum. 4. There were good phenotype-season relationships shown by both sexes in all species, except for female E.abusivus and E.nemorum, with paler insects being more abundant during the warmer summer months. 5. Female, but not male, E.arbustorum collected at inland sites were on average paler than those collected at coastal sites. This observation is considered with respect to temperature during the developmental stages. 6. The function of colour plasticity in hoverflies is discussed with reference to the need to maintain optimal thermal conditions for activity.