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GENERAL NOTES

Journal of the Lepidopterists' Society 50(4), 1996, 345-347

A STUDY OF HYBRIDIZATION BETWEEN COLIAS ERATE AND C. EURYTHEME (PIERIDAE)

Additional key words: sex ratio, variation, phylogenetic relationships.

Hybridization among some species of Colias is common in nature, and many species of the genus can be hybridized under laboratory conditions (e.g., Gerould 1943, Hovanitz 1949, 1955, Remington, 1954, Ae 1959). In 1992, I had the opportunity to conduct hybridization experiments between Colias erate Esper and Colias eurytheme Boisduval. The source of the C. eurytheme stock was Sweet Briar College in Virginia, USA; the source of C. erate was Aichi Prefecture, Japan. Hybridization studies were conducted in the rearing room of the Biological Laboratory, Nanzan University, at 25°C and using fluorescent lights to create an 18 hr:6 hr light-dark regime.

Three white C. erate females were reared from eggs laid by a field collected, white female; the females emerged 13 May 1992. The females were placed in a screen cage (ca. 25 x 25 cm) with several field collected males of C. eurytheme. One of the females mated with a male almost immediately, and copulation lasted more than an hour. This female laid about 100 eggs on white clover, Trifolium repens L. (Fabaceae), all of which hatched. I reared the larvae of these Fl hybrids on white clover and alfalfa, Medicago sativa L. (Fabaceae) in the rearing room. From 10 to 23 June 1992, 25 males and 25 females of Fl adults were obtained (Fig. 1, Table 1). Concurrently, a brood of C. eurytheme males and females was reared from eggs from the Virginia stock on white clover and alfalfa.

Using the Fl adults, additional field collected C. erate, and the progeny of the Virginia stock, the following pairings were achieved: (a) three matings between Fl siblings; (b) two matings between C. eurytheme females and Fl males; (c) one mating between an Fl female and a C. eurytheme male; (d) one mating between a C. erate female and an Fl male; (e) one mating between an Fl female and a C. erate male (Table 1).

Among the mated females, one of the Fl hybrid sibling matings laid one egg; one Fl female paired with a C. erate male laid 7 eggs, and one C. eurytheme female paired with an Fl hybrid male laid 21 eggs. None of these eggs turned red, as is typical for developing Colias eggs, and all were presumed to be infertile. Three C. eurytheme females reared from eggs laid by the Virginia field collected females paired with field collected C. erate. One laid about 100 eggs and another laid about 40 eggs, none of which were fertile.

Colias erate has a yellow ground color and a sex-limited female white form. Japanese C. erate males and females have irregular yellow blotches in the marginal black band (Fig. 1), similar to female C. eurytheme. Colias eurytheme has an orange ground color and a sex-limited white form. In contrast to C. erate, the marginal band in male C. eurytheme is uniformly black, without yellow blotches (Fig. 1). The Fl males generally were intermediate in ground color (Fig. 1), however, yellow blotching in the marginal band was variable from almost absent to blotching as in C. erate (Fig. 2). White females of C. erate and C. eurytheme are extremely similar, as were the Fl white females (Fig. 3). Eggs, larvae, and pupae of C. erate and C. eurytheme are nearly identical, as were those of the Fl hybrids to the parental stock.

In my previous hybridization experiments, Fl hybrid males between C. eurytheme and C. interior Scudder were fertile, although the Fl sex ratio was predominantly males (26 males:l female). The sex ratio of Fl hybrids between C. erate females and C. eurytheme males was 1:1, but they were infertile. Two C. eurytheme females that paired with C. erate males laid only infertile eggs. Although additional experiments are necessary to corroborate these results, it appears that C. erate from Japan and C. eurytheme from the United States are not closely related. There are many species of Colias in the world, many of which closely resemble each other morphologically. Hybridization studies such as this may be useful in identifying phylogenetic relationships among these morphologically similar species.

I wish to express my sincere gratitude to Charles L. Remington, Yale University, and

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Journal of the Lepidopterists' Society

Volume 50, Number 4

347

TABLE 1. Results of hybridization attempts between Colias erate and Colias eury-theme. EU = C. eurytheme; Coe, ER = C. erate.

Eggs            Eggs %                    Fl adults

Female parent                              Male parent                          Kind of mating                           laid                fert.                     male/female

25         25

Edward D. Dodson, Notre Dame University, for direction during my graduate studies, and the guidance of the late Taku Komai, Kyoto University, during my undergraduate study. I am especially grateful to Lincoln R Rrower for assisting in the collection of C. eurytheme, and to Etsuo Nakajima, Nagoya, Japan, for assisting me in rearing the butterflies used in this study.

Literature Cited

Ae, S. A. 1959. A study of hybrids in Colias (Lepidoptera, Pieridae). Evolution 13:64-88.

GEROULD, J. H. 1943. Genetic and seasonal variations of orange wing-color in Colias butterflies. Proc. Am. Phil. Soc. 86:405-438.

HOVANITZ, W. 1949. Interspecific matings between Colias eurytheme and Colias philodice in wild populations. Evolution 3:170—173.

----------. 1955. Hybridization and species blending in the butterfly genus Colias. Proc. XIV

Inter. Congr. Zool: 140-141.

REMINGTON, C. L. The genetics of Colias (Lepidoptera). Adv. Genetics 6:403-450.

SHIGERU A. Ae, Biological Laboratory, Nanzan University, 18 Yamazatocho, Showaku, Nagoya, 466, Japan.

Received for publication 1 August 1995; revised and accepted 8 March 1996.

FlGS. 1—3. Adult Colias erate, C. eurytheme and their hybrids. 1, C. erate female (upper left), C. eurytheme male (upper right), Fl hybrid (below). 2, variation among Fl hybrids of C. erate x C. eurytheme. 3, female white forms: C. erate (upper left), C. eurytheme (upper right), Fl hybrid (below).