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1960

Journal of the Lepidopterists' Society

5

A STUDY OF HYBRIDS BETWEEN PAPILIO XUTHUS AND THE P. POLYXENES-MACHAON GROUP

by Shigeru Albert Ae

Papilio xuthus Linne (pl.l : fig.2) is found commonly but only in East Asia. It is distributed in Japan, Korea, Manchuria, Amur, China, North Burma, Formosa, Luzon, Guam, etc. It is very common in most parts of Japan, but becomes rare toward the northern part of Hokkaido. It seems also uncommon in hot regions, as in Formosa. In Japan, it is usually not found in the high mountains, unlike P. hippocrates Felder & Felder (Fig. 1), which is found in the high mountains as well as the lower places. The adult of P. xuthus resembles the adult of the P. machaon group, and P. xuthus is usually placed in the P. polyxenes-machaon group. However, the pupa and larva of P. xuthus do not resemble the pupae and larvae of species of that group. They rather resemble the pupae and larvae of P. protenor demetrius Cramer, P. rnemnon thunbergii von Siebold, P. helenus nicconicolens Butler, and P. macilentus Janson in Japan. The pupae and larvae of these four Japanese black swallowtails resemble each other closely. The larval and pupal resemblances between P. xuthus and P. helenus Linne were pointed out by Remington (1960). These four black swallowtails are Rutaceae feeders as is P. xuthus. Therefore, the phylogenetic position of P. xuthus m the genus Papilio is interesting and a study of it may help in analyzing the evolutionary process of species in the genus.

Dr. C. L. Remington obtained very important data in this problem by interspecific crossings between P. xuthus and the polyxenes-machaon group (1960). Namely, he succeeded in obtaining one male hybrid between P. hippocrates and P. xuthus and two male hybrids between P. polyxenes Linne and P. xuthus. Since P. hippocrates is very common in Japan as well as P. xuthus, it is very easy to work on hybridization of these two species in Japan. Therefore, the writer obtained many hybrids of this kind in 1958 and 1959 at Nanzan University, Nagoya, Japan, following Dr. Remington's work in 1957. The writer also obtained some hybrids between P. xuthus and P. polyxenes (Fig.3) and between P. xuthus and P. ffhrucei Edwards" (Fig.4). The data are not sufficient to give a final conclusion on the relation between P. xuthus and P. machaon relatives, and crossing experiments are still in progress in the writer's laboratory, along with hybridization tests between P. xuthus and the four above-mentioned Japanese black swallowtails. However, it takes years to complete this kind of work. Therefore, the writer presents here the data mainly in genetics of interspecific characters on the hybrids between P. xuthus and P. machaon relatives obtained in 1958 and 1959, so that they are available for the workers in the same field.

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Ae: Papilio xuthus hybrids

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Pupae of P. polyxenes and P. "brucei" were reared by the writer in 1957 at Yale University and the Rocky Mountain Biological Laboratory respectively and sent to the writer at Nanzan University in winter by the kindness of Dr. Remington. The so-called "brucei" is the high mountain Papilio of Colorado and is considered by Remington not to be true brucei (Maeki & Remington 1960: p. 196). A permit to import these pupas to Japan was given to Nanzan University by the Agricultural Ministry of Japan. P. hippo-crates pupae were obtained by the rearings of local wild larvae and eggs from local wild females in the fall of 1957 and 1958, and wild P. xuthus pupae were collected from Karatachi {Poncitrus trifoliata Rafin., Rutaceas) fences in Nagoya and Osaka in the winters of 1957-1958 and 1958-1959. Wild adults of P. hippocrates and P. xuthus in the vicinity were also used in 1958 and 1959, especially males.

The prefix of individual designation used for P. "brucei', P. hippocrates, P. polyxenes, and P. xuthus are respectively B, H, P, and X. The individual designation of a female was also used as the designation of its brood. When a female mated twice or more, this brood was separated; e.g. H-3a and H-3b.

All the matings were obtained by hand-pairing (Clarke & Sheppard, 1956). Eggs were obtained from females in glass cylinders on potted food plants. The containers were placed under incandescent and fluorescent lights. For the rearing of larvae, insect cages about 30 cm. cubed were used. These experiments were carried on exclusively in a double screened rearing room to prevent any accidental release of American butterflies in 1958. This room was windowless and lighted by fluorescent and incandescent lights usually during the day time but with no definite period. The rearing of the larvae of the hybrids between P. hippocrates and P. xuthus in 1959 was carried on at the windowside of the laboratory. There was no control of temperature or humidity, and no heater was used in either room.

Remington (1960) pointed out that P. hippocrates should be placed as a species separate from P. machaon, and the writer has no objection on it.

Hybrids Between Papilio xuthus and P. hippocrates

Nine P. hippocrates females were hand-paired with P. xuthus males in 1958. Only two of the females, H-3 and H-ll, laid fertile eggs. Broods H-3a and H-ll were obtained from them. One more female laid a few eggs but they were all infertile. H-3 was remated with another P. xuthus male and later again with a P. hippocrates male, and Broods H-3b and H-3c were obtained. Seven P. xuthus females were hand-paired with P. hippocrates males in 1958. Four females laid eggs, but only one, X-26, laid fertile eggs. The fertility of matings is shown in Table 1. An egg is yellowish white when laid, and if it starts a development, a brown mottling or ring appears (Remington, 1960). This phenomenon was used as an indication of fertilization. When a larva is well formed in an egg shell, the egg color turns black.

All larvae which hatched in Brood X-26 were put into plastic containers with Seri (CEnanthe stolonifera DC, Umbelliferae) and Karatachi. The

1960

Journal of the Lepidopterists' Society

7

larvae which chose Karatachi were reared on Karatachi. The number of larvae which started to feed on Seri was larger than the number which started to feed on Karatachi. Fifteen larvae of Brood H-3a were reared on Seri, 14 on Natsumikan (Citrus natsudaidai Hayata) and 4 on Karatachi, respectively. The larvae which were reared on Natsumikan were moved to Seri at their 4th instar, because of the shortage of fresh Natsumikan leaves. The larvae of H-3b were reared on Mitsuba (Crytota'nia japonica Hassk., Umbelliferae), and the larvae of H-3c were reared on Seri. The number of pupae which were obtained from these rearings and the pupal lengths are shown in Table 3. Although the eggs of Brood H-3c were laid after the female mated with a wild P. Hippocrates male for more than one hour, the larvae from them were identified as hybrids. Broods H-3a, X-26, and X-27 (from eggs laid by a wild P. xuthus) were reared at the same time (April to May), and the pupae of X-27 were larger than the pupae of the hybrids. Therefore, the small size of the hybrid pupae are not seasonal. Since three pupae of P. xuthus, which were obtained from the larvae reared on Seri, were as large as the other P. xuthus reared on Karatachi, effects of food plant on hybrid larvae do not seem to be the cause of the small size. [P. Hippocrates larvae feed on Umbelliferae and occasionally on Rutaceae, and P. xuthus feeds on Rutaceae in nature in Japan (Esaki & Shirozu, 1951)]. No difference in developmental rates was observed in these rearings. The P. Hippocrates larvae were not reared at the same time, but their summer form, which comes from spring larvae, is usually larger than the summer form of P. xuthus. The hybrid butterflies which emerged from these small pupae were consequently very small. Loss during the larval stage in hybrids was noticeable. Some definitely died of diseases, but some deaths could have been due to hereditary causes from hybridization. Some pupae were malformed to some extent. The larvae of Brood H-ll were reared outdoors under a net and fed on Natsumikan branches. Some of them reached the 4th instar, but all died without having another molt.

Some additional data were obtained in 1959. Ten P. Hippocrates females were hand-paired with P. xuthus males. Seven of the females laid eggs, and the eggs laid by five of them contained some fertile ones. Twelve P. xuthus females were hand-paired with P. Hippocrates males. Nine of the females laid eggs, and the eggs laid by four of them contained some fertile eggs. Table 2 shows the fertility of these matings. Only one larva, which hatched from the eggs laid by female H-29-13, was reared on Seri and reached the pupal stage, This was sent to Mr. K. Maeki for chromosomal study. The two larvae which hatched from the eggs laid by female H-29-16 were killed accidentally. Fifteen larvae which hatched from the eggs laid by female H-34-5 were reared on Seri, and 6 pupae were obtained; four of them emerged. Forty of the larvae from female X-70 were reared on Seri and 14 pupae were obtained. A few were sent to Mr. Maeki for chromosomal study, and 5 adults were obtained from the remaining pupae. Seven and eight larvae from the same female were reared respectively on Inuzansho (F agar a schinifolia Engl., Rutaceae) and cultivated carrot (Daucus carota L.). All of them died dur-

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Ae: Papilio xuthus hybrids

Vol.14: no.l

ing their larval stages. Four larvae from female X-97 were reared on Citrus, but died during their larval stages. Seven larvae from female X-103 were reared on cultivated carrot; one reached its pupal stage but did not emerge. Eleven larvae from female X-107 were given a choice among cultivated carrot, Seri, and Inuzansho. Four, four, and three started to feed on cultivated carrot, Seri, and Inuzansho respectively. However, all of them died during the larval stages. The main cause of larval loss during the above rearings seems to be virus diseases. These hybrid pupae were as small as the hybrid pupae in 1958.

The larvae of P. xuthus and P. hippocrates are completely different in color pattern, and the hybrid larvae share some characters with one parent and show intermediate expression in other characters. The writer's observations essentially coincide with Remington's (1960). In general, the hybrid larvae resemble P. xuthus in the first 2 instars and show somewhat intermediate (rather close to hippocrates) appearance in the last instar (Plate 2: figs. 1-3; Remington 1960: plates 2, 3). The mature larva of P. hippocrates is extensively variable in the width of the black area. Sometimes the black area covers almost all the green area and sometimes the green area is predominant. This variation seems environmental and the same tendency appears in the hybrid larvae.

The pupae of P. xuthus and P. hippocrates are also quite different. The hybrid pupae show somewhat intermediate appearance. The ground color of P. hippocrates pupae is brown or green and that of P. xuthus is variable, but able to be classified as green, brown, or orange. The ground color of the hybrid pupae is as variable as P. xuthus, but they are either green or brown and no orange appears, although the numbers of the pupae examined are not enough to conclude that orange pupae are absent in hybrids. Otherwise, the writer's observations coincide with Remington's (1960) in the detailed characters (Remington 1960: plate 3).

The twenty-nine adults which emerged were all males (Table 1). Remington (1960) pointed out that this hybrid closely resembles summer P. xuthus in general appearance, but the writer's hybrids more resemble summer P. hippocrates females than either sex of summer P. xuthus. Summer P. hippocrates females are darker in melanin pigmentation and paler in the ground color than summer P. hippocrates males. The ground color of summer P. hippocrates female is indistinguishable from that of the present hybrids. Remington (1960) also made character-by-character comparisons among the male parental species and the hybrid. The writer's hybrids coincide with Remington's in 8 detailed characters (2nd pale wedge from fore-wing apex in postmedian row, 2 transverse pale spots in forewing discal cell, hindwing anterior cell, and hindwfng submarginal lunules resemble P. hippocrates; length of pale zone of hindwing anal eyespot, hair along anal margin of hindwing, and basal V2 antennal club resemble P. xuthus; and hindwing anal eyespot is intermediate). Four points of difference from Remington's analysis are as follows: 1) ground colors are somewhat vari-

1960                               Journal of the Lepidopterists' Society                                     9

able in the hybrids and in general they are intermediate between the parental species; 2) four pale streaks in forewing discal cell, which are present in P. xuthus and absent in P. Hippocrates, are always present in the hybrids but they are not so clear as in P. xuthus; 3) black-striping along veins of fore-wing and hindwing, which is broad in P. xuthus and narrow in P. Hippocrates are rather intermediate than most like xuthus; 4) outer tail fringe, which is pale in P. xuthus and is dark in P. Hippocrates, is variable in the hybrids — in some it is Hippocrates-like, in some it is xuthus-\ike, and in others it is intermediate (Figs. 5, 6; Remington 1960: plates 2, 3).

One prominent reciprocal difference was found in the pre-pupal stage. Many hybrids between P. Hippocrates female and P. xuthus male succeeded in making a silk girdle passed around the thorax in their prepupal stage and consequently normal pupation took place. However, no hybrid between P. xuthus female and P. Hippocrates male succeeded in making a girdle in the prepupal stage and the pupae hung only by the tip of the abdomen or often dropped. Consequently almost all pupae were malformed to some extent and most of the hybrid butterflies failed to extend their wings fully.

Hybrids between P. polyxenes Female and P. xuthus Male

Five hand-pairings of this kind were obtained and eggs were also obtained from all the matings. However, only two matings were fertile, and from these Broods P-l-70 and P-l-73a were obtained. The second female was remated with another male P. xuthus and again it laid fertile eggs (Brood P-l-73b). The fertility of matings is shown in Table 1. All larvae of Brood P-l-70 were put into a plastic container with Seri and Karatachi when they hatched. The number of larvae which started to feed on Seri was larger than the number which started to feed on Karatachi. Larvae were reared on either food plant as selected by the larvae themselves. This rearing was carried on at the same time as the rearings of 1958 reported in the previous section. Their developmental rates showed no difference in comparison with the rearings in the previous section. Twelve pupae were obtained from Brood P-l-70. Only one pupa was obtained from Brood P-l-73a and none from Brood P-l-73b. The hybrid pupae were very small, and consequently the butterflies were too (Table 2).

The larvae of P. polyxenes and P. Hippocrates are very similar except in the color of the larval spots. These are always orange to red in P. Hippocrates and orange or yellow in P. polyxenes. This color was always yellow in the P. polyxenes which the writer used. Consequently, in the hybrid larvae, these larval spots were always yellow. In the other characters, they were exactly the same as with the hybrids between P. Hippocrates and P. xuthus (PL 2: figs. 4a, 4b).

The pupae of P. polyxenes and P. Hippocrates are indistinguishable and both of them have green or brown ground color. The pupal color of the hybrids is brown or green, and the other characters are the same as with the

10                                              Ae: Papilio xuthus hybrids                               Vol.14: no.l

1H := P. hippocrates; X tz F. xuthus; P r= P. polyxenes; B .= P. "brucei".

2Used for chromosomal study at its pupal stage.

3Both larvae killed accidentally.

4A few were used for chromosomal study at their pupal stage.

f)Many larvae died because of the inadequate food plants used for these tests.

HNo female hybrids were obtained from any of the crosses.

1960                                   Journal of the LepidopteristsJ Society                                       11

Table 2. PUPAL LENGTHS OF PAPILIO SPECIES AND THEIR HYBRIDS

hybrid pupae between P. hippocrates and P. xuthus (Remington 1960: plate 3).

The adults (10 males) are almost identical to normal P. polyxenes males except in size, and the writer's observations coincide with Remington's (1960) in character-by-character comparisons, in which the hybrids resemble P. polyxenes in 11 detailed characters, P. xuthus in 1, and are intermediate in 2. One more character is added here. This character is transverse pale spots in the forewing discal cell. P. xuthus has two clear spots and P. polyxenes has one slight spot. The hybrids have one or two spots, which are not clear.

Twelve sib matings were obtained from P. polyxenes Brood P-l by hand-pairings. Eggs were obtained from 11 pairs of them, and 5 laid fertile eggs. The fertility of these matings is shown in Table 1. Unfortunately diseases killed all of the offspring in their larval or pupal stages.

Hybrids between P. "brucei" and P. xuthus

Ten P. "brucei' females were hand-paired with P. xuthus males. Five of them laid eggs but fertile eggs were obtained from only 1 female, B-3-9. Five P. xuthus females were hand-paired with P. "brucei" males. Although two oi them laid eggs, eggs from only one of them, X-16, were fertile. The fertility of the matings is shown in Table 1. Larval foods were as follows: X-16, two by Natsumikan, two by Mitsuba; B-3-9, 27 by Seri, 3 by cultivated carrot. Losses during the larval stages were many. Table 2 shows the number of pupae obtained and their lengths. They were again very small. These rearings were carried on at the same time as the rearings in 1958, reported in previous sections. Their developmental rates showed no difference in comparisons with other rearings in the previous sections. Five male hybrids were obtained (Table 1, Fig. 8).

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Table 3. INTERSPECIFIC DIFFERENCES BETWEEN $ PAPILIO XUTHUS AND $ P. "BRUCEI" AND THEIR EXPRESSION IN THE HYBRID*

Character

1.   Ground color:

2.  Basal 2/3 of FW discal cell:

3.  Basal i/2 of cell Cu2 of FW:

4.   Marginal x/2 of cell Cu2 of FW:

5.   FW cell 2nd A:

6.  2nd pale wedge from FW apex in p.m. row (cell R5) :

7.   FW submarginal lunules:

8.  Blackstriping along veins of FW & HW:

9.  HW anterior cell (cell Sc + Ri) :

10. Submarginal lunules of HW:

xuthus

creamy white 4 pale streaks

1 pale streak

J-shape spot 1 pale streak

with black median spot

most much longer than broad broad

brucei

Hybrid

yellow                   hit

dark with pep-   dark with 4 pale

pering of yellow   streaks in some

indi. (int)

dark with pep-   dark with slight

pering of yellow   peppering of yellow (bru-)

rectangular spot   xu-

dark with pep-   peppering and

pering of yellow   spot (int) in base and marginal spot

spotless                  bru

about as long as int broad

bisected by broad no black patch bru median black patch on basal 2/3 slender                        fat                         bru

♦Symbols are: xu c= exactly like xuthus, bru'.= exactly like "brucei", inti= intermediate, xu- trr most like xuthus, bru- i= most like "brucei", FW t=: forewing, HW c=z hind-wing, p.m.

postmedian. Names of cells follow "Comstock-Needham" system.

The larvae of P. "brucei" and P. polyxenes are similar, and the larval spots were all yellow in the P. "brucei' which the writer used. The hybrid larvae were exactly the same as the hybrid larvae between P. polyxenes and P. xuthus. The pupal ground color of P. "brucei" is brown or green, and that of the hybrids was also brown or green. The hybrid pupae were indistinguishable from the hybrid pupae between P. polyxenes and P. xuthus. The general appearance of the hybrid butterflies is intermediate between the parental species. Table 3 shows the character-by-character comparisons in the male parental species and the hybrids in adult stage. The same system was used with Remington's Tables 2 and 3 (1960) and the "Comstock-Needham" system was used for the names of wing cells. The hybrid butterflies were intermediate in 4 detailed characters, resemble P. xuthus in 2, and resemble

1960

Journal of the Lepidopterists' Society

13

P. " brucei' in 4. The ground color was intermediate, but it was variable in some extent, therefore it is close to P. xuthus in some and close to P. "brucei" in other.

Twelve hand-pairings were obtained between P. "brucei' females and males. Eggs were obtained from 8 pairs, and the eggs from 3 pairs included fertile eggs. Unfortunately diseases killed all of the larvae.

Backcrosses of Hybrids to P. xuthus Females

One male each of Broods H-3a and P-l-70 was hand-paired with P. xuthus females which emerged in the laboratory in 1958. One male of Brood B-3-9 was hand-paired with two females of P. xuthus, also in 1958. However, only one female which mated with H-3a-5 laid any eggs (3), which were all infertile. Two males of Brood H-34-5 were hand-paired with P. xuthus females in 1959; one of the females laid one egg but it was infertile.

Discussion

There is no definite information for a minimum duration of a successful copulation. In about 150 inter- and intra-specific hand-pairings in Papilio, which the writer has obtained, fertile eggs were obtained only from the matings which lasted about or more than one hour. Therefore, all matings which lasted less than about one hour were omitted from the present data temporarily. However, there is another problem concerning spermatophore formation in mating. A P. hippocrates female, H-3, was hand-paired three times, the first and the second time with P. xuthus and the third with P. hippocrates. All lasted more than one hour. It laid some fertile eggs after each mating. After the third mating, it laid 81 eggs, but only 8 were fertile and 3 hatched. These larvae, however, proved to be a hybrid between P. hippocrates and P. xuthus. Therefore, it is quite possible that the third mating was not effective, probably by improper or no formation of a spermatophore. The writer has a few more exampes of the same kind in other Papilio matings. However, the writer is still unable to separate spermatophores which were produced by different males in a female body in Papilio, although it is easy in Colias. Therefore, more studies should be done concerning the failure to lay fertile eggs after a mating of sufficient duration.

The absence of females, namely the heterogametic sex, from the three kinds of hybrids, is a clear example of Haldane' Rule. There is some possibility of the appearance of female sex if a large enough number of hybrids is obtained. However, male predominancy seems to be fairly definite.

Although a few backcrosses were tried, more experiments are necessary to find out if these hybrids are sterile.

More larvae chose to feed on Seri (Umbelliferae) than Karatachi (Ruta-ceae) in hybrids between P. xuthus and P. hippocrates or P. polyxenes. These phenomena may tell the food plant preference of hybrid larvae. However, the

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softness of Seri leaves in comparison with Karatachi which was not so fresh could also be the reason for it.

1 he conditions of the rearing room were not controlled. However, since the three kinds of hybrids and their controls were reared at the same time in 1958, the small sizes of the hybrids were not environmental. P. polyxenes and P. "brucei" which were used for the controls were not reared by the adult stage, but the size of their mature larvae, which were obtained in large numbers was as great as for P. xuthus and P. hippocrates mature larvae. The developmental rates of the hybrids and the pure parental species were apparently identical, although a minor difference in the rates may be found when they are checked more precisely.

The high inviability of the Fx hybrids between P. xuthus and the three species of the P. polyxenes-machaon group in the writer's experiments, in comparison with the viability of the hybrids within the P. polyxenes-machaon group (Clarke & Sheppard 1953, 1955; Remington 1958; Ae in press), indicates that P. xuthus is not so closely related to the P. machaon group as many taxonomists have presumed. These data support Remington's data and discussion in his 1960 paper. The egg fertility was rather high in some crosses such as 98% in Brood X-70, 95% in Brood X-26, 94% in Brood H-3a (all xuthus X hippocrates) and 94% in Brood X-16 {xuthus X brucei). When the eggs started to develop, the larva seems to be fully formed inside of the egg shell in a high percentage in many broods. However, the actual hatch of the larvae dropped extensively except in one case, 90% hatching in Brood X-26. This phenomenon may indicate weakness of the hybrid larvae or some differences in egg shell or in the mechanism of emerging from the egg shell between the parental species. More studies are necessary in this point. Many hybrid larvae were apparently lost by virus diseases. However, they seemed more resistant to virus disease than the larvae of pure species of the P. polyxenes-machaon group. Some of the larvae of P. xuthus were also killed by virus diseases. But P. xuthus seemed not to be affected by the same virus which kills the P. polyxenes-machaon group, although this is very difficult to prove. If it is really so, this is another negative datum on the relationship between P. xuthus and the P. polyxenes-machaon group. Egg fertility and hatchability of the controls were rather low in some crosses (Table 1). These phenomena are probably the effect of inbreeding or of shortage of spermatozoa. But the effect of laboratory rearing or virus diseases in developing eggs may not be denied and these could have a similar effect on hybrids.

P. hippocrates larvae are occasionally found feeding on Rutaceae in Japan, but it is very difficult to rear the larvae on Rutaceae. The writer had no success in getting an adult reared on Rutaceae thus far, although more species of Rutaceae should be checked. P. xuthus can be reared on Seri (Umbellxferae), but the results are not so good. Therefore, although the hybrid can be reared on either Rutaceae or Umbelliferae, if Rutaceae-feeding species of the P. poly-

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Journal of the Lepidopterists' Society

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xenes-machaon group are used for hybridization with P. xuthus, better results may be obtained.

Most probably one could conclude that P. xuthus does not belong to the P. poly xenes-machaon group from the data of Remington (1960) and the writer in this paper. However, it is possibly more closely related to the P. poly xenes-machaon group than the present data indicate.

P. hippocrates and P. xuthus are sympatric in Japan. The writer has observed in Nagoya many P. hippocrates males flying about at the place where P. xuthus females were emerging. Yet, there is no report on natural hybridization. This was confirmed by Dr. T. Shirozu, T. Iwase and other Japanese butterfly specialists seeing the writer's hybrid. This may indicate the importance of mating behavior, because hand-pairing bypasses these behavior differences.

Summary

1.     Of nineteen Papilio hippocrates females which were hand-paired with P. xuthus males, 7 laid fertile eggs. Twelve male butterflies were reared from these eggs.

2.     Of 19 P. xuthus females which were hand-paired with P. hippocrates males, 5 laid fertile eggs. Seventeen male butterflies were reared from these eggs.

3.     The characters of the larvae, pupae, and adults of the above Fx hybrids between P. hippocrates and P. xuthus were compared to those of the similar hybrids which were obtained by Remington (1960) and to their parental species. The hybrid larvae and pupae have intermediate appearances in general between the parental species. The ground color of the pupae is brown or green. The above hybrid adults are also intermediate in the general aopearance and differ in 4 detailed characters from Remington's hybrid. The writer's hybrids resemble xuthus in 4 detailed characters, hippocrates in 4, and are intermediate in 4.

4.     Of five P. polyxenes females which were hand-paired with P. xuthus males, two laid fertile eggs. Ten male butterflies were obtained from these eggs.

5.     The characters of the larvae, pupae, and adults of the above Fx hybrids were compared to those of the similar hybrids which were obtained by Remington and to their parental species. The larvae and pupae are generally intermediate of the parental species as in Remington's hybrids. The hybrid males are almost identical to normal P. polyxenes males, and detailed characters coincide with Remington's similar hybrids. In addition, transverse pale spots in the forewing discal cell have an intermediate expression between the parental species and are variable.

6.     Of 10 P. "brucei" females which were hand-paired with P. xuthus males, one laid fertile eggs. Five male butterflies were reared from these eggs.

7.     Of 5 P. xuthus females which were hand-paired with P. "brucei" males, one laid fertile eggs but no adult was reared from them.

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8.     The larvae and pupae of P. "brucei" are indistinguishable from those of P. polyxenes; the larvae and pupae of their hybrids with P. xuthus are also like those of P. polyxenes X P. xuthus. The general appearance of the male hybrids between P. "brucei" and P. xuthus is intermediate between that of the parental species. In detailed characters, they resemble "brucei" in 4, xuthus in 2, and are intermediate in 4.

9.     The inviability of the above three kinds of hybrid is high in general. Egg fertility is rather high in some crosses of all three kinds, but the drop in hatchability is very large. The few backcross attempts were not successful.

10.     The larvae of these hybrids feed on both Rutaceae and Umbelliferae. The developmental rates of these hybrids and their parental species are the same. The sizes of these hybrids are very small in comparison with the parental species.

11.     The adults of these hybrids are all males and Haldane's Rule applies here.

12.     P. xuthus seems not to belong to the P. polyxenes-machaon group, since they are not closely related with the three species of the P. polyxenes-machaon group used in these hybridization experiments. But it may be somewhat more closely related with other species of the P. machaon group.

13.     There is no record of a natural hybrid between P. hippocrates and P. xuthus in Japan, although the two species are extensively sympatric in Japan.

Acknowledgements

The writer wishes to express his sincere gratitude to Dr. Charles L. Remington, Department of Zoology, Yale University, for his advice and reading this paper in manuscript. He also kindly sent the writer a manuscript copy of his 1960 paper, so that the writer could revise a part of this paper. The writer is grateful to the Agricultural Ministry of Japan for a permission to import American Papilio pupae for experiments reported here, to Rev. Francis Bures, S. V. D., for help in writing this paper, and to the Rocky Mountain Biological Laboratory for facilities given. A fund was supplied from the Ministry of Education in Japan in 1959.

Literature Cited

Ae, S. A., in press. A study of hybrids in the Papilio machaon group.

Clarke, C. A., & P. M. Sheppard, 1953. Further observations on hybrid swallowtails. Supplement to the Entomologist's Record 65: No. 9.

............, 1955. A preliminary report on the genetics of the machaon group of swallowtail butterflies. Evolution 9: 182-201.

............, 1956. Hand-pairing of butterflies. Lepid. News 10: 47-53.

Esaki, T., & T. Shirozu, 1951. Shin Konchu 4: no. 9.

Maeki, K., & C. L. Remington, 1960. Studies of the chromosomes of North American Rhopalocera. 1. Papilionidae. Journ. lepid. soc. 13: 193-203.

Remington, C. L., 1958. Genetics of populations of Lepidoptera. Proc. X. int. congress ent. 2: 787-805.

.....___, 1960. Wide experimental crosses between Papilio xuthus and other species.

Journ. lepid. soc. 13: 151-164.

Biological Laboratory, Nanzan University (Catholic University of Nagoya),

Showaku, Nagoya, JAPAN

PA PI LI 0 HYBRIDS

PLATE 1

Fig.l — Papilio Hippocrates $ (summer form) ; fig.2 — P. xuthus $ (summer form) ; fig.3 — P. polyxenes $ ; fig.4 — P. "brucei" $ ; fig.5 — $ F, hybrid Hippocrates X xuthus (H-3-3) ; fig.6 — anal eyespot of same Fx hybrid (H-3-3), enlarged; fig.7 — $ Fj hybrid polyxenes X xuthus (P-1-70-1) ; fig.8 — $ Fj hybrid "brucei" X xuthus (B-3-9-2). Upperside at left of each figure, underside at right.

PLATE 2

PAP1LI0 HYBRIDS

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PiPILlO 5th INSTAR LARV/E Fig.la, lb — P. Hippocrates; fig. 2a, 2b — P. xuthus; fig.3a, 3b, 3c — FL hybrid hippocrates X xuthus; fig.4a, 4b — F1 hybrid poly-xenes ^ xuthus. Each rigure shows lateral view above, dorsal view below.