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Journal of the Lepidopterists' Society 33(3), 1979, 167-169

A DOCUMENTATION OF BIENNIALISM IN BOLORIA POLARIS (NYMPHALIDAE)1

John H. Masters

25711 North Vista Fairways Drive, Valencia, California 91355

ABSTRACT. Capture/noncapture records of Boloria polaris at Churchill, Manitoba over a 46-year timespan provide documentation that the species (at least at Churchill) is biennial, where adults fly only in odd-numbered years.

Biennialism in insects is that situation where an insect's life-cycle takes two years to complete so that imagos are produced only after two years of pre-imaginal development. It may be accompanied by biennial flights when, in a given locality, adults fly only in alternate years (periodical flight); or it may be accompanied by annual flights. Unless biennial flights are involved, biennialism is extremely difficult to perceive in nature without carefully working out the insect's life history. Annual flights may occur when the species is only partially biennial or when two allochronic populations are involved. Documented cases of regular biennialism are very rare in Lepidoptera and heretofore have been confined to two species of moth (Lasiocampa quercus callunae in Europe and Coloradia pandora lindseyi Barnes and Benjamin in North America) and a few species of Satyridae (e.g., Oeneis macounii Edwards, Oeneis nevadensis Felder and Felder, Oeneis jutta Hubner, Erebia claudina Borkhausen, and Erebia ligea Linnaeus). For a review of periodical flight behavior in other insects, see Bulmer(1977).

In working on a study of butterflies occurring at Churchill, Manitoba (Masters, 1971), it became evident to me that Boloria polaris stellata (Masters) is biennial at Churchill and since that time, I have accumulated enough data to document this fact rather well. This is the first documentation of periodical biennialism in Nymphalid butterflies. It has been suggested, and recent collecting data tends to support the contention, that several other species of Boloria (e.g., B. distincta Gibson and B. chariclea Schneider) and the arctic populations of one species of Hesperiidae (Hesperia manitoba borealis Lindsey) will also turn out to be biennial.

Churchill, Manitoba, since the opening of the Hudson Bay Railroad in 1930, has been a classic arctic collecting locality. Because Churchill has been collected repeatedly for a span of 46 years, it is possible to document the capture and noncapture data for Boloria polaris from

1 Originally submitted and accepted for publication in 1971; publication delayed due to manuscript loss in the mail. Revised to incorporate new data.

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Journal of the Lepidopterists' Society

Table 1. Capture/noncapture records of Boloria polaris at Churchill, Manitoba.

Expeditions recording Boloria polaris

Expeditions failing to record Boloria polaris

1933 (A. V. Harper)

1937 (G. S. Brooks) 1939 (G. S. Brooks) 1939 (B. Wilk) 1941 (G. S. Brooks) 1943 (G. S. Brooks)

1947 (T. H. Freeman)

1951 (A. B. Klots & R. D. Bird)

1961 (F. H. & P. W. Chermock)

1963 (F. H. & P. W. Chermock)

1967 (J. A. Ebner)1

1969 (A. E. Brower)

1971 (C. D. Ferris)

1932 (A. V. Harper) 1936 (H. E. McClure)

1940 (G. S. Brooks) 1942 (G. S. Brooks) 1944 (G. S. Brooks) 1946 (G. S. Brooks)

1952 (A. B. Klots & R. D. Bird)

1968  (C. S. Quelch)

1969 (J. H. Masters)2

1970 (J. H. Masters) 1970 (C. McCullough)2

1974 (D. Oosting & D. Parshall) 1976 (D. Oosting & D. Parshall) 1978 (J. Troubridge)

1  Specimens presumably not taken by Ebner personally.

2  Expeditions in late July and August, too late in the year to expect to find Boloria polaris

27 collecting expeditions. These data are tabulated in Table 1. Information was gleaned from 14 expeditions to Churchill in odd-numbered years; 13 of which recorded B. polaris (only my very short trip in late July 1969 did not). On the other hand, I have documented 13 expeditions to Churchill in even-numbered years, none of which recorded B. polaris, even though 12 of them were at the proper time of year. I have also scanned both private and institutional collections for specimens of B. polaris that might have been collected at Churchill in even-numbered years, and have failed to find a single specimen. The evidence is thus conclusive, albeit circumstantial, that Boloria polaris has an odd-year only biennial flight at Churchill.

Additional records of Boloria polaris accumulated from other localities suggest that it is probably biennial everywhere, but may be subject to random geographic alternation of odd-year and even-year broods. These data are summarized in Table 2. Unfortunately, no other region in the arctic has been collected as extensively as Churchill for butterflies, over so long a period, and a comparable documentation of the biennial flight of B. polaris at any additional locality cannot be made. The collecting reports of the Alaska Lepidoptera

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Table 2. Circumpolar capture records of Boloria polaris, noting year of capture. Records, other than Churchill, based on specimens in the American Museum of Natural History, New York and Carnegie Museum, Pittsburgh.

1 One specimen 22 July 1957 by A. T. Washburn.

Survey, over a ten year period (1967-1977) establish reasonably well, however, the biennial flight of the species on Ester and Murphy Domes near Fairbanks, Alaska.

Literature Cited

Bulmer, M. G. 1977. Periodical insects. Am. Nat. Ill: 1099-1117. MASTERS, J. H. 1971. The butterflies of Churchill, Manitoba. Mid-Continent Lepid. Ser. 25: 1-13.