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60

Journal of the Lepidopterists' Society

hours; the thermoregulatory problems of A. fatima have been discussed (Emmel 1972, Evolution 26: 96-107). Gradual heat gain on sunny days leads to shade-seeking behavior by late afternoon and shady perches also provide nocturnal shelter from winds. It is known that for some insects living in hot climates, such as desert cicadas, gains in body heat result in definite periods of movement into shade and subsequent quiet periods (e.g., Heat & Wilkin 1970, Physiol. Zool. 43: 145-154). Dark butterflies in lowland tropical dry climates may have similar temperature-response problems.

The above observations and comments suggest that aggregative behavior of A. fatima is an adaptive response to highly localized climatic or abiotic factors, having little or nothing to do with biotic factors such as vertebrate predators. A biotic result of such behavior, however, may be the maintenance of a cohesive adult population that survives until the following rainy season to oviposit on foodplants as they leaf out. This idea has been discussed with respect to S. karwinski (Muyshondt & Muyshondt 1974 op. cit.) and it may be generally true for other secondary habitat or pasture-dwelling tropical nymphalines which pass the dry season in the adult stage.

This fieldwork was funded by N.S.F. Grant GB-33060 and friends of the Museum, Inc. of the Milwaukee Public Museum.

Allen M. Young, Invertebrate Division, Milwaukee Public Museum, Milwaukee, Wisconsin 53233.

Journal of the Lepidopterists' Society 33(1), 1979, 60-64

BISTON BETULARIA, OBLIGATE F. INSULARIA INDISTINGUISHABLE FROM F. CARBON ARIA (GEOMETRIDAE)

It is well known that there is sometimes difficulty in phenotypically recognizing and scoring f. insularia of Biston betularia. On the one hand it may be confused with carbonaria (Kettlewell 1973, The Evolution of Melanism, Oxford, London) and on the other with "typical," particularly in the Isle of Man (Bailey et al. 1973, Entomologist 106: 210-214). To help clarify the matter, various scoring methods have been devised for insularia, e.g., that of Lees and Creed (1977, Heredity 39: 66-73, and used by us), where I1 is the lightest and I3 the darkest. Neveretheless, difficulties remain, and Lees and Greed (1977) report a brood, B/574, in which a mating between two insularia IV'typical" heterozygotes produced 66 "typical," 149 F insularia and 77 carbonaria which were thought to be F/F homozygotes. They also quote Bowater (1914, J. Genet. 3: 299-315) who crossed a wild carbonaria male with a "typical" female, and all the resulting progeny were dark insularia, which is consistent with the F/F hypothesis.

The present note shows that this cannot always be the explanation since the brood to be described could not have produced F/F homozygotes. On 13 June 1976 a a female "typical" (Fig. la) was caught in a mercury vapor trap on Hilbre Island near West Kirby, Wirral, England. She was placed in a tin for the following five nights and laid a few eggs, but these were infertile. On the night of 19 June 1976, she was put in a hanging cage with a male insularia (Fig. lb) (score F, confirmed by Lees and Creed, pers. comm.), which had been caught in the mercury vapor trap at Caldy, Wirral. Mating took place the same evening and the female then laid freely (brood 14672). After she died on 28 June 1976 her body was found to contain a single sper-matophore only.

Table 1. brood 15090

The 1977 matings from brood 14672. All "dark" insects were indistingui

Brood number

Offspring

Form and brood of Px $

Form of provenance of Px d

dd

"typical" "dark" "typica

Figs. 1-2. Biston betularia. la. 9 "typical," parent brood 14672; lb. S insularia, I3, parent of br rood 14672; 2b. 9 insularia, F, of brood 14672.

Figs. 3-4. Bistort betularia. 3a. $ carbonia, M.V. trap-caught, 1977 Caldy; 3b. $ sulana of brood 14672, indistinguishable from carbonaria; 4b. 9 m^ana of brood 1

64

Journal of the Lepidopterists' Society

Brood 14672 produced 394 insects, the moths emerging between May and July 1977. There was clear-cut segregation between "typical" (90 $ $; 97 2 2) and "dark" (100 S S • 107 $ $ ).

Since carbonaria is dominant to insularia, and "typical" is recessive to both, and because the brood segregated in a 1:1 ratio, "typical" to "dark," the male parent must have been insularia/"typical" and the "dark" offspring must all have been insularia/"typical" heterozygotes.

We found great difficulty in scoring the brood. Some of the insularia males undoubtedly had a sparse scattering of white scales and rather light hindwings (Fig. 2a), but they lacked the white scales on the thorax or abdomen characteristic of insularia. Others appeared to us to be quite indistinguishable from carbonaria and we cannot agree that the two can easily be separated, ". . . since in carbonaria, when the white scales are present on the forewing, they are distributed to form a thin, unbroken transverse line across the middle of the forewing" (Steward 1977, Ecol. Entomol. 2: 231-243). The insularia females in brood 14672 (Fig. 2b) present even more of a problem, because they are normally darker than the males and we should have scored nearly all of them as carbonaria (Figs. 3b and 4b).

We appreciate that in expert hands specimens may be scored more competently, but had the "dark" males of brood 14672 been "trap caught" (Fig. 3a), we (and we think others) would have scored many of them (see Fig. 4a) as "carbonaria," and Creed (pers. comm.) agrees with this view.

Kettlewell (1973, The Evolution of Melanism, Oxford, London) thinks that those insularia which are difficult to distinguish from carbonaria axe in a minority, as are the pale insularia misclassified as dark "typical." He further thinks that because of the small numbers in these two categories, the frequency figures for "typical" and insularia are largely unaffected. However, it is difficult to be sure of this since we do not know how often misscoring takes place, and different observers in the same locality do, in fact, obtain very different results when recording the frequency of the three forms (see Kettlewell, 1973, op. cit., table 9: 2).

Creed (pers. comm.) thinks that carbonaria as scored in the wild is perhaps as heterogeneous as insularia. We agree with this, and feel that the possibility of mis-scoring of males should be seriously considered when unusual frequencies of carbonaria and insularia are reported. (The misscoring of females is much less important as they rarely come to mercury vapor light and never to an assembly trap.)

Sib matings and backcrosses using brood 14672 were set up and their results are given in Table 1. Moths which were obligatory insularia/'"typical" heterozygotes again were almost always indistinguishable from wild-caught carbonaria, as were insularia/carbonaria heterozygotes. Furthermore, there was no detectable difference between any of these "dark" insects and those in brood 15088, which must have contained insularia homozygotes. An additional mating was set up from this stock in 1978 using the insularia female (I3) from brood 15090. These results will be reported later.

We are grateful to the late Dr. E. R. Creed and to Dr. D. R. Lees for scoring a sample of our brood and for their helpful comments, and to the Nuffield Foundation, The Royal Society and the Science Research Council for continued support.

Note added in proof: Brood 15490 using this female I3 mated to a male "typical" is segregating (so far) cleanly I3 and "typical" with no carbonaria.

Sir Cyril A. Clarke, Hon. Research Fellow, Department of Genetics, University of Liverpool, England.

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