Adult silkmoths captured in northwestern Ontario and tentatively identified as Hyalophora columbia (Smith) were found to resemble H. gloveri nokomis (Brodie) which occurs as far east as Winnipeg, Man. Habitat studies showed that the larvae of the northwestern Ontario moths are not strictly larch feeders as are the larvae of typical H. Columbia.
The dorsal thoracic tubercle colour of typical fifth instar H. Columbia larvae is red. Matings between typical H. Columbia and H. cecropia (L.) have produced fifth instar larvae with only reddish-orange tubercles. However, matings of male moths from northwestern Ontario with H, cecropia females have produced fifth instar larvae with reddish-orange, light orange, or yellow dorsal thoracic tubercles. Further matings of northwestern Ontario males with H. euryalis (Boisd.) and typical H. Columbia females have established the presence in northwestern Ontario of a colour polymorphism of which the phenotypic colour components are red, reddish orange, and yellow.
The fifth instar dorsal thoracic tubercle colour of H. gloveri nokomis larvae is yellow and it is proposed that the yellow tubercle colour of the northwestern Ontario larvae has originated from the influx of genes from the nearby H. gloveri nokomis population.
The evidence presented in this paper points to the existence of an intergrade population between H. gloveri nokomis and H. columbia in northwestern Ontario.