Bilateral Gynandromorph of Hyalophora cecropia
(Lepidoptera: Saturniidae) in Nova Scotia

The recognition of a lepidopterous gynandromorph in nature is a rare event, even for an extensively collected group such as the Saturniidae. Hessel (1964) described a bilateral gynandromorph of Automeris io (Fabricius) taken in Connecticut in 1962, and referred to the capture of bilateral gynandromorph Eacles imperialis (Drury) in New Jersey and of Callosamia promethea (Drury) in Indiana, both taken in 1962.

Smith (1998) described rearing a bilateral gynandromorph of Antheraea polyphemus (Cramer) from a cocoon in California in 1994, and suggests that it may have been the result of second generation inbreeding and rearing conditions. Frings (1897) briefly described a gynandromorph of Hyalophora cecropia (Linnaeus) emphasizing differences in the pattern and color of wings between male and female sides of the specimen.

Gynandromorphs generally develop a sex abnormality early in their development, thus it is possible for individuals to become bilaterally differentiated, with one side of the body being male, the other side female (Scriber and Evans, 1988). This bilateral condition may be caused by a loss of a Z chromosome in the first cell division of the fertilized egg, or by development of a binucleate ovum (Blanchard and Descimon, 1988). In sexually dimorphic species, the female side of the gynandromorph develops disproportionately larger in size because female cells are larger. Differences in secondary sex characteristics such as in the form of the antennae and the abdominal claspers can be quite obvious (Manley, 1971).

Here, I report the capture, at a black light, of what appears to be a bilateral gynandromorph of H. cecropia (Linnaeus), in early July, 1997, in Halifax County, Nova Scotia. The purpose of this note is to present a brief description and photograph of the specimen. A series of male and female specimens from various locales within the province, currently in the author's personal collection or in the Reference Collection of the Nova Scotia Museum of Natural History, were also examined.

The characters studied are forewing (size, color, postmedial lines, discal spot, and red scale character); hindwing (color, discal spot size and shape); and head (antennae). Basic quantitative characteristics of the two sides are as follows: length of female antennae = 8mm versus length of male antennae = 1 cm; length of forewings on both sides of the specimen are approximately identical at 6cm, however, the width of the female forewing from costal margin to tornos (anal angle) is wider by 1.5 cm. One distnctive character is the width of the red postmedial band on hindwings. In females the band is 4mm wide, but in males it is only 2 mm.

In dorsal view the female (left) and male (right) sides are distinctly different, especially the antennae, which are larger and more strongly pectinate on the male side. Sexual differences in the wing pattern are also maintained between the two sides. The wings of the gynandromorph are intermediate in size with respect to wings of normal specimens, those of the female being slightly larger than those on the male side. However, the difference in size between the gynandromorph are less than the size difference between wings of normal males and females.

The male forewing is also more angled, accentuating its curved apex. The ground color of the basal area of both forewings is predominantly grey, concolorous with the median area and outlined distally by the black antemedial line. The basal region of the male forewing is more extensively suffused with red scalation than the female forewing. The wider red postmedial band of both female wings is distinct from the narrower red band of the male wings. The outer wing margin of the female forewing contains two black spots along its inner edge; these spots are less prominent on the male side. The white zig-zag and black subapical spot ("eye-spot") near the forewing apex are more elongate on the female side.

The marginal pattern of the male forewing and hindwing is in sharp contrast to the diffuse, obscure pattern of the same areas on the female side. Pale cream crescents (discal spots) outlined with black and red are present on both the forewing and hindwing of both sides. However, the discal spot on the forewing of the female side is more elongate than that spot on the male side, whereas the hindwing discal spot on the female side is broader than on the male hindwing.

There is no clear line of demarcation between the two sides of the head, thorax or abdomen. In particular the abdomen is not divided on the dorsal midline and is tapered in shape posteriorly, appearing more similar in shape to the abdomen of a normal male than to those of normal females. Without denuding the abdomen and thorax it is not possible to determine any concealed abnormalities on the cuticle in those regions.

When compared to normal male and female specimens, all quantitative qualities of the two sides of the specimen described above fall within the range of variation found for the respective sexes. I conclude that the specimen is a bilateral gynandromorph. The specimen will be deposited in the Reference Collection of the Nova Scotia Museum of Natural History.

I acknowledge the interest and encouragement given by Andrew Hebda, Curator of Zoology, Nova Scotia Museum of Natural History, and thank him for his critical review of the manuscript. I thank John E. Rawlins and two anonimous reviewers for helpful suggestions on the manuscript.

Derek Bridgehouse was serving as Research Associate, Nova Scotia Museum of Natural History, at the time of this writing.

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