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Journal of the Lepidopterists' Society 32(4), 1978, 289-303

INTER-SPECIFIC HYBRIDIZATION INVOLVING LIMENITIS

ARCHIPPUS AND ITS CONGENERIC SPECIES

(NYMPHALIDAE)

Austin P. Platt

Department of Biological Sciences, University of Maryland Baltimore County, 5401 Wilkens Avenue, Catonsville, Maryland 21228

George W. Rawson

10405 Amherst Avenue, Silver Spring, Maryland 20902

George Balogh

3607 No. 98th Street, Milwaukee, Wisconsin 53222

ABSTRACT. The occurrence of 43 natural hybrids involving Limenitis archippus and its congeneric species (L. arthemis-astyanax, L. lorquini, and L. weidemeyerii) is reviewed. Nine of these hybrid records are reported for the first time. Data based on laboratory crosses are given in order to document the purported wild hybrid specimens. Reasons underlying the observed natural hybridization are suggested and their evolutionary implications are discussed.

Species of the North American genus Limenitis readily undergo interspecific hybridization both in nature and in the laboratory (Edwards, 1882; Scudder, 1889; Field, 1904, 1914; Newcomb, 1907; Gunder, 1934; Remington, 1958, 1968; Platt, 1975). The occurrence of 22 natural hybrids and the laboratory documentation of them in crosses involving either 1) L. arthemis arthemis Drury or 2) L. arthemis astyanax Fabri-cius X L. archippus Cramer have been reviewed and discussed by Monroe (1953); Grey (1968); Shapiro and Biggs (1968); Platt and Greenfield (1971), and Greenfield and Platt (1974). Since then, Johnson (1974) and Arbogast (1976) have reported two other wild-collected L. arthemis astyanax X L. archippus hybrid specimens. Likewise, the natural occurrence of four L. lorquini Boisduval X L. archippus hybrids (Gage, 1970; Perkins and Gage, 1970) and five L. weidemeyerii Edwards X L. archippus hybrids (Cross, 1936, 1937; Simpson and Pettus, 1976) have also been recorded. Lab-bred equivalents of these wild hybrids are shown in Fig. 1.

In this paper we shall review these past records and will report records of nine other naturally occurring Limenitis hybrids involving L. archippus, a species broadly sympatric with other members of the genus. We will also present new information obtained from laboratory

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DORSAL

VENTRAL

1 cm

Fig. 1. Representative lab-bred Fi male hybrid specimens. 1) Form "arthechip-pus" brood 893, No. 17, May 7, 1977; 2) form "weidechippus" brood 576, No. 7, Sept. 4, 1971; 3) lorquini $ X archippus $ (unnamed hybrid), brood 987, No. 1, Sept. 8, 1978. These, and all other lab-bred specimens, were reared on either Salix babylonica L. or Prunus serotina Ehrh.

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Fig. 2. Distribution map of 43 known wild, inter-specific Fi hybrids involving cross-breeding with L. archippus collected from "prior to 1872" through 1976. All records for which the sex is known are males. These hybrids are widely distributed geographically. Touching symbols represent two (or more) specimens from the same locality. Most hybrids have been collected late in the season (August-November). Complete data for these hybrids are given in Tables 1, 1A, and 2. (Map reproduced with the permission of the Missouri Botanical Garden, St. Louis, Mo.).

crosses recently made by Piatt, followed by a brief discussion of the relationships between L. archippus and its close relatives.

Tables 1, 1A and 2 summarize the collection data for all 43 records of wild hybrids involving L. archippus and its congeneric species. The geographic distributions of the various hybrid forms have been plotted in Fig. 2. The new hybrid locality records given in Table 1 are those from Maine (hyb. form "arthechippus" Scudder), Wisconsin, Illinois, Michigan, New Jersey, Virginia, and Florida (hyb. form "rubidus" Strecker). The specimens from Idaho, Illinois, Michigan, New Jersey, Virginia, and Florida probably represent state records for these hybrids.

The Florida record represents the first report of a natural hybrid between L. a. astyanax Fabricius and the sub-species L. archippus floridensis Strecker. The live specimen was observed circling a shrub willow along the edge of Mud Lake by G.W.R. while he was lunching

Table 1. Continued.

1 This table excludes 20 records previously listed by Piatt and Greenfield (1971).

2 Numbered records have not been previously reported by Newcomb (1907), Piatt and Greenfield or Arbogast (1976).

Table 1A. Records of 20 previously wild-caught Limenitis arthemis-astyanax hybrids, modified 80. Dashes indicate that information was not available. (Reproduced by permission of the autho

rovince or tate

County

Locality or Township

Date

No. Collector &/o & Sex1 collection

Quebec

Maine

New Hampshire

Manitoba

New York

New York Total

Pennsylvania

Pennsylvania

Massachusetts Massachusetts New York

New York

L. a. arthemis X L. archippus ("arthechippus" Scudder)2

Penobscot Cheshire

Tompkins Albany

Berks

Westmoreland

Norfolk Middlesex

"Eastern" (Catskills?)

L. a. astyanax X L. archippus ("rubidus" Strecker) —                            Prior to 1872

Jeanette

Wellesley Sherborn Brooklyn

Aug., 1896 Sept. 9, 1913

1 $       T. L. Mead

Coll.

1 $       Barnes col

1 $      A.M.N.H.

16*       A. L. Babl

1 $      Barnes col

1                —

1 Insofar as is known, all specimens collected to date have been males.

2 Eight male arthechippus were reared by Field (1914) from an L. archippus $ X L. a. arthemis cently by Piatt.

3 A $ L. a. astyanax X d L. archippus were collected in copula Aug. 26, 1957 in a barnyard by The two specimens are in the A.M.N.H. (Klots, 1959; Dr. F. H. Rindge, pers. comm.).

Table 1A. Continued.

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DORSAL

VENTRAL

I         I

1cm

Fig. 3. 1) Wild-caught and 2) lab-bred male specimens of L. arthemis astyanax X L. archippus floridensis Fi hybrids (form "ruhidus"). Data for the lab-bred specimen are brood 986, No. 1, Sept. 19, 1977 (Data for wild-caught specimen are given in Table 1).

with members of the Florida Audubon Society in the northeastern portion of the Ocala National Forest. He recognized the specimen as an "off-color" Limenitis and investigated it further. The insect then settled on the willow shrub. Since he had no net, George made a "desperate strike" at it with his cap, knocking the butterfly to the ground and collecting it. The specimen is illustrated in Fig. 3, along with a similar, single specimen recently reared by A.P.P. in the laboratory from a hand-paired cross between a Maryland astyanax ? X a floridensis $ (from a stock obtained just east of the Everglades [near Home-

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DORSAL                                    VENTRAL

MH 1 cm

Fig. 4. Small, weak, and faded lab-bred Fi female hybrid specimens, dorsal and ventral views. 1) Form "weidechippus," brood 576, No. 1, Aug. 28, 1971; 2) form "rubidus," brood 648, No. 4, July 26, 1973.

stead] in southern Florida). Astyanax evidently is relatively uncommon in central Florida. Near his home at New Smyrna Beach (Volusia Co.), G.W.R. has seen only two specimens of astyanax during the past 20 years. Also, F. Rutkowski (pers. comm.) recently collected a $ astyanax 1.5 miles north of Shamrock (Dixie Co.) in Florida, and he mentioned other records from as far south as Dade Co. (Kimball, 1965). Possibly such scarcity of one (or both) species accounts in part for such interspecific hybridization (Simpson and Pettus, loc. cit.).

So far as is known, all of the wild hybrids thus far collected have been males, although five broods containing small, faded, weak (and often malformed) Fi females (Fig. 4) were reared at UMBC in June and July, 1973 by crossing inter-specific strains having different geographic origins (Maryland L. astyanax $ $ X Vermont L. archippus

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$ $ ). Among these broods, there were a total of 39 (27%) Ft females among 143 hybrid "rubidus" progeny. Two of the larger broods, involving sibling female astyanax and the same male archippus parent, yielded 1:1 sex ratios.

Earlier crosses reported by Piatt (1975) showed that such interspecific crosses, in which strains from the same (or closely adjacent) northeastern geographic origins were crossed, gave rise to complete adult heterogametic (female) inviability. However, robust females of the "arthechippus" and "rubidus" hybrid phenotypes (Fig. 5) also have been obtained by backcrossing Fx hybrid males to females of the three parental forms (arthemis, astyanax, and archippus, respectively). Such backcrosses often have low viability, but sometimes yield relatively large numbers of progeny (Piatt, loc. cit.). Although fertile crosses have been obtained in all possible reciprocal combinations, crosses using L. arthemis, astyanax, lorquini, or weidemeyerii 9 $ x L. archippus $ $ have been the easiest to effect in the laboratory using hand-pairing. The fact that such a pairing also has been seen in the wild (Klots, 1959; Table 1A) suggests that these inter-specific hybrid crosses may occur most often in this direction in nature, as well.

Table 1 indicates that eight of the nine previously unreported arthemis-astyanax X archippus hybrids, like most of those reported earlier, were collected during the late summer and fall months (August-November). Only one (from New Jersey) was collected in June, a time suggesting that it most likely arose from an over-wintering larva. Thus, these new records, as well as the previous ones, support the contention that the ecological and behavioral barriers normally preventing inter-specific hybridization in Limenitis tend to break down later in the season (Greenfield and Piatt, loc. cit.). This break down may well be correlated with the onset of facultative larval diapause in Limenitis which occurs during the third instar. Thus, it seems as if those individuals most often selecting mates of the wrong species are the very ones which seem to be "genetically mal-adapted" to their environment (that is, they are the ones which are not diapausing at that time of year when they are

Fig. 5. Representative robust, lab-bred hybrid-type backcross females. 1) L. arthemis 9 X Fi hybrid "arthechippus" $ ("arthechippus-\ike" morph), brood 63c, No. 4, July 30, 1968; 2) L. archippus $ X Fi hybrid "arthechippus" $ ("arthe-chippus-\ike" morph), brood 915, No. 45, June 13, 1977; 3) L. arthemis $ X Fi hybrid "rubidus" $ ("proserpina-hke" morph), brood 95B, No. 4, Dec. 26, 1968; 4) L. archippus 9 X Fi hybrid "rubidus" $ ("rubidus-\ike" morph), brood 757, No. 10, Sept. 15, 1975. Such backcross females also occur in parent-type morphs (see Piatt, 1975).

Tablb 2. Records of nine wild hybrids involving the two western banded species of Lime respectively) X L. archippus.

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supposed to be doing so). Such hybridization, perhaps, represents a "last chance" effort to reproduce.

The similar rare natural hybrids reported between both of the western banded Limenitis (L. lorquini and L. iveidemeyerii) and L. archippus are listed in Table 2. The eight known dates of siting or capture suggest once again that either 1) the hybrids emerged early enough in the year (June and July dates) so that it is a relative certainty that the larvae from which they arose over-wintered in hibernacula, or 2) the specimens were collected in the late summer or fall months. Gage's (pers. comm.) collection dates for the small "hybrid swarm" near Richland, Washington (Table 2) suggest that the four lorquini X archippus hybrids, in fact, represent progeny from at least three different matings. The same may be said for the four "weidechippus" records from Colorado, as well. All of these wild western hybrids are males, and they closely resemble hybrid from *'arthechippus" in possessing a partial postmedial white band dorsally (Fig. 1). Two crosses between Colorado weidemeyerii 9 9 X Massachusetts archippus S S have been made by laboratory hand-pairings to date, yielding 22 $ $ and nine $ ? (seven of the latter being malformed). All of these F/s, although showing some phenotypic variability, are referrable to hyb. form "weidechippus" (Piatt, unpub. data). During the past summer two crosses between Oregon L. lorquini $ $ X Maryland L. archippus $ $ were carried out. All 16 Fi progeny were males. An additional cross involving an Fi hybrid, arthemis-lorquini $ (Massachusetts X Oregon stocks, respectively) X Maryland archippus $, yielded 21 male hybrid-like progeny.

Thus, L. archippus, which is broadly sympatric with its congeners, will occasionally hybridize with all of the other allopatric species of Limenitis in nature. However, such crosses evidently are rare, leading to the supposition that morphological, behavioral, visual, and possibly pheromonal cues, as well as habitat isolating mechanisms, normally operate to prevent such inter-specific hybridization. These barriers against gene exchange between the viceroy and its close relatives sometimes tend to break down, usually when one or both species are rare, and often toward the end of the breeding season, at times when the majority of developing Limenitis larvae are entering diapause.

Laboratory data show that inter-specific strains having different geographic origins may be genetically more compatible than similar strains from the same locality, as judged by either the presence or absence of adult females in the Fi generation. Thus, genetic incompatibility between the viceroy and its congeneric species is viewed as being of local

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origin, suggesting that archippus may have arisen from a banded ancestral species by the process of sympatric speciation. (The senior author would appreciate hearing from members of the Society who may have knowledge of other records of wild Limenitis hybrids.)

Acknowledgments

We are grateful to those individuals who provided us with information regarding the collection of hybrid specimens as noted in Table 1. We thank Dr. A. Maizels for sending the floridensis stock and Mr. P. J. Kean for making the inter-specific hand-pairing involving this strain. Mr. S. J. Harrison and Mr. T. Williams have assisted with the insect rearing and preservation. We thank Dr. W. D. Field, Dr. D. C. Ferguson of the U.S.N.M., and Dr. K. Bagdonas of the University of Wyoming for the information relating to hyb. form "weidechippus"'. Mr. E. Gage kindly provided data and color photos of the lorquini X archippus hybrids.

Literature Cited

Arbogast, R. T. 1976. Capture of a hybrid Limenitis arthemis astyanax X L. archippus (Nymphalidae) in southern Georgia. J. Lepid. Soc. 30: 4.

Cross, F. C. 1936. (No title). Hobbies 41: 112.

----------. 1937. Butterflies of Colorado. Proc. Colo. Mus. Nat. Hist. 16: 3-28.

Edwards, W. H. 1882. Descriptions of new species of butterflies found in the United States. Papilio 2: 45-49.

Field, W. L. W. 1904. Problems in the genus Basilarchia. Psyche 11: 1-6.

----------. 1914. Hybrid butterflies of the genus Basilarchia. Psyche 21: 115-117.

Gage, E. V. 1970. A record of a naturally occurring Limenitis hybrid (Nymphalidae). J. Lepid. Soc. 24: 270.

Greenfield, J. C, Jr. & A. P. Platt. 1974. Report of the capture of an additional hybrid between Limenitis arthemis astyanax and L. archippus (Nymphalidae). J. Lepid. Soc. 28: 72-75.

Grey, L. P. 1968. (No title). In No. Amer. Ann. Summary, News Lepid. Soc, No. 3, p. 19.

Gunder, J. D. 1934. A check list revision of the genus Basilarchia Scud. (Lepid.: Rhopalocera). Canad. Entomol. 66: 39-48.

Johnson, K. 1974. An aberrant interspecific hybrid of Limenitis (Nymphalidae) from Wisconsin. J. Lepid. Soc. 28: 163-165.

Kimball, C. P. 1965. The Lepidoptera of Florida, in Arthropods of Florida and neighboring land areas. Fla. Dept. Agric, Gainesville, Fla. Vol. 1: 363 pp.

Klots, A. B. 1959. A mixed mating of two species of Limenitis Fabricius (Lepidoptera, Nymphalidae). J. N.Y. Entomol. Soc. 67: 20.

Monroe, B. L. 1953. A hybrid Limenitis. Lepid. News 7: 53.

Newcomb, H. H. 1907. Description of a new variety of Limenitis ursala. Psyche 14: 89-91.

Perkins, E. M. & E. V. Gage. 1970. On the occurrence of Limenitis archippus X L. lorquini hybrids (Nymphalidae). Journ. Res. Lepid. 9(4): 223-226.

Platt, A. P. 1975. Monomorphic mimicry in nearctic Limenitis butterflies: experimental hybridization of the L. arthemis-astyanax complex with L. archippus. Evolution 29: 120-141.

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Platt, A. P. & J. C. Greenfield, Jr. 1971. Inter-specific hybridization between

Limenitis arthemis astyanax and L. archippus (Nymphalidae). J. Lepid. Soc.

24: 278-284. Remington, C. L. 1958. Genetics of populations of Lepidoptera. Proc. Tenth Int.

Congr. Entomol. 2: 787-805. ----------. 1968. Suture-zones of hybrid interaction between recently joined biotas.

Evol. Biol. 2: 321-428. Scudder, S. H. 1889. The butterflies of the eastern United States and Canada,

with special reference to New England. Vol. 1. Publ. by the author, Cambridge,

Mass. pp. 250-305. Shapiro, A. M. & J. D. Biggs. 1968. A hybrid Limenitis from New York. J. Res.

Lepid. 7: 149-152. Simpson, R. G. & D. Pettus. 1976. Records of Limenitis hybrids from Colorado.

J. Res. Lepid. 15(3): 163-168.

Journal of the Lepidopterists' Society 32(4), 1978, 303-304

TAENIDIA INTEGERRIMA, A NEW FOODPLANT RECORD FOR PAPILIO POLYXENES (PAPILIONIDAE)

Host plants recorded for the larval stages of Papilio polyxenes Fabricius include a wide variety of species in the family Umbelliferae. Although the dominant foodplants in the northeastern United States are plants naturalized from Europe, e.g., Daucus carota Linnaeus and Anethum graveolens L. (Tyler, 1975, The Swallowtail Butterflies of North America, Naturegraph Publishers, Heraldsburg, CA), a number of endemic species have been documented as foodplants. Tietz (1972, An Index to the Described Life Histories, Early Stages, and Hosts of the Macrolepidoptera of the Continental United States and Canada, A. C. Allen, Sarasota, FL) lists Cicuta bulbifera L., Cicuta maculata L., Angelica atropurpurea L., Osmorhiza claytoni (Michx.), Osmorhiza longi-stylis (Torr.), Oxypolis filiformis (L.), Spermolepis divaricata (L.), Ptilimnium capil-laceaum (Michx.), and Sium suave Walt, among the native umbellifers; Cryptotaenia canadensis (L.) has recently been reported as a foodplant as well (Scriber and Finke, 1978, J. Lepid. Soc. 32: 236-238). The majority of these species are characteristically found in rich damp woods (Osmorhiza spp.) or wet thickets and swamps.

The native umbellifer Taenidia integerrima (L.) Drude (yellow pimpernel), hitherto unrecorded as a host plant for P. polyxenes but reported as a host plant of the recently described sibling species P. joanae (Heitzman, 1973, J. Res. Lepid. 12: 1-10), is a plant of dry, gravelly slopes and rocky hillsides (Fernald, 1950, Gray's Manual of Botany, 8th ed., American Book Co., NY). On June 22, 1977, one fifth instar larva of P. polyxenes was found feeding in a patch of T. integerrima growing on a dry, exposed slope bordering a road which cuts through Coy Glen, a forested area 3 km west of Ithaca, Tompkins Co., New York. Two additional fifth instar caterpillars were found in the same patch two days later. All three caterpillars were collected and reared to pupation on T. integerrima collected from the Coy Glen site. Pupation was virtually synchronous on June 24, 1977, indicating that the caterpillars may have developed from eggs laid at approximately the same time, possibly by a single female. On July 2, 1977, one adult male ichneumonid, Trogus pennator (Fabr.), a well-known parasitoid of P. polyxenes (Heinrich, 1964, Canad. Ent. Suppl. 29: 807-853), emerged from each of the three pupae.