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Journal of the Lepidopterists* Society
A MIGRATION OF KRICOGONIA CAST ALIA (PIERIDAE) IN NORTHERN MEXICO1
George W. Byers
Dept. of Entomology, University of Kansas, Lawrence
Kricogonia castalia Fabricius ranges from northern South America (Venezuela) through Central America and Mexico into Texas and through the Caribbean region (Haiti, Puerto Rico, Jamaica) occasionally to southern Florida. It has been reported (often under the synonymous name, K. lyside Latreille) as common in Texas, and stray individuals have been recorded as far north as Colorado, Nebraska and Illinois (Ehr-lich and Ehrlich, 1961). According to Godman and Salvin (1887-1901, p. 150), K. castalia (as K. lyside) "does not appear to be a very common insect" in Mexico and Central America.
A migratory flight of this species, observed in central Tamaulipas on 11 July 1961, suggests it sometimes becomes at least locally abundant in northern Mexico. The butterflies were seen moving generally from northwest to southeast, toward the Gulf of Mexico. These observations were made about 80 miles inland from the Gulf, along Highway 101, commencing about 14 miles northeast of Ciudad Victoria near Giiemes. From there, the width of the stream of Kricogonia was measured as 53.5 miles on to the northeast. I have no estimate of the length of the emigrating stream. Since the terrain along this part of the highway is rather flat with only light and scattered vegetation, the butterflies, especially when moving in dense groups, could be seen several hundred yards to either side of the road. Their bright yellow on pale yellow color also made them easy to see from afar.
Density of the migration varied within the broad zone described, yet for the entire 53.5 miles some butterflies were always in sight, moving generally toward the southeast. The widest of the dense streams within the migration was 9.5 miles across. Since the butterflies flew generally within six feet of the ground, and mostly about two or three feet above the surface, large numbers of them were struck and killed by our vehicles as we drove across the emigrating stream at about 50 miles per hour. It is not easy to estimate the density of insects in such an emigration, but my counts made at the time suggest about 1100 butterflies per minute were crossing an average mile of front along the highway (or perhaps some 55,000 per minute were passing a line at right angles to the direc-
1 Contribution no. 1462 from the Department of Entomology, University of Kansas, Lawrence. I wish to thank Dr. Orley R. Taylor for reading the original manuscript of this note and making useful suggestions, particularly concerning dissection of females.
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tion of the stream). A sample of 18 specimens was easily taken in a couple of minutes.
At the time of these observations, the weather was hot and the sky was partly cloudy, the gathering clouds producing a light sprinkle of rain approximately 65 miles northeast of Ciudad Victoria, near mid-afternoon, just before we drove out of the migration. There was a light to moderate breeze from east-northeast, so that the butterflies, on a northwest to southeast course, were moving slightly into the wind.
In the sample collected, there was a 3.5 to 1 ratio of females to males (14 9, 4 $ ). Three females with large abdomens were dissected, and it was found that none contained any eggs whatsoever (yet large amounts of what appeared to be fat) and that each contained the hardened remains of one large spermatophore. In the males, there was noticeable variation in the extent of the black spot near the costal margin of the hind wing. Adults of K. castalia have been seen feeding on blossoms of mesquite, and Klots (1951) reports lignum vitae (Guaiacum officinale) as larval food for this species in Puerto Rico. Unless this emigration had come a long way, it seems the food plant must have been some common member of the semi-desert flora.
Migrations of pierid butterflies are frequently observed and reported in the entomological literature; however, as far as I can determine, this is the first record of a migration of a species of Kricogonia (there are only two species in the genus). Recent books on insect migration (Williams, 1958; Johnson, 1969) do not mention the genus.
Literature Cited
Ehrlich, P. R. and A. H. Ehrlich. 1961. How to know the butterflies. W. C. Brown Co., Dubuque, Iowa.
Godman, F. D. and O. Salvin. 1887-1901. Biologia Centrali-Americana. Lepidop-tera-Rhopalocera, vol. 2.
Johnson, C. G. 1969. Migration and dispersal of insects by flight. Methuen & Co., Ltd., London.
Klots, A. B. 1951. A field guide to the butterflies. Houghton Mifflin Co., Boston.
Williams, C. B. 1958. Insect migration. Macmillan Co., New York.