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1962
Journal of the Lepidopterists' Society
99
NOTES ON CERTAIN LEPIDOPTERA OVIPOSITING ON PLANTS WHICH ARE TOXIC TO THEIR LARV^
by R. Straatman
It has been observed that females of certain species of butterflies occasionally lay eggs on plants, generally belonging to the same family as the natural hostplant, but on which the larvae did not survive. Such behaviour was described by other authors (Dethier 1942, Edwards 1935, Remington 1952) and was recently mentioned of two Sumatran Papilionidae (Straatman & Nieuwenhuis 1961). In Queensland, Australia it has been observed in the following four species.
1. Troides priamus richmondius Gray is locally common in Southeastern Queensland. In March 1960, at the promontory of Burleigh Heads, 60 miles south of Brisbane, where this species is very localised, several females v/ere observed laying eggs on Aristolochia elegans Mast. This plant has been introduced from Brazil and is common in the area. A total of 70 eggs were collected from several of these plants and a similar number was left untouched. From the eggs, 61 larvae hatched in the laboratory at Samford, 14 miles N. N. W. of Brisbane, and 40 of them were reared in the insectary on A. elegans growing in pots. Six larvae died in the first instar, 22 in the second and the remainder in the third instar. The other 21 larvae had been released on plants of A. elegans growing outside, along the creek. About a week after their release, the plants were inspected and a number of first instar larvae found; later inspections, however, showed only few larvae in the second instar and none were found beyond this instar. The leaves showed but little feeding damage. In the third week of April the plants from which the eggs were collected at Burleigh Heads, were inspected carefully, but apart from many eggshells suggesting a good hatch, not a single larva was found and the leaves showed only little damage caused by feeding. Freshly laid eggs, however, were again present. A few hundred yards from these plants, larvae of T. priaraus were found in all ins tars on Aristolochia prxvenosa F. Muell., a native species and apparently their natural hostplant. Here it forms vines climbing into the forest canopy.
Another locality were T. priamus occurs, but where A. elegans appeared to be absent, is Tamborine Mountain (1800 ft., 22 miles N. W. of Burleigh Heads). Here, A. prsevenosa is locally common in the rainforest and numbers of eggs and larvae of T. priamus were collected and transferred to Samford. The larvae were released on A. elegans growing
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in pots in the insectary, At first they refused to eat and were very restless, but after two days most specimens started an irregular feeding, However, most of these larvae died in the second week of their transfer, while larger specimens survived for four weeks, growing smaller and weaker until they died. All the larvae which had hatched from the eggs died in the first instar,
2. Eurycus cressida cressida Fabricius is a common species in the Brisbane area where its host is Aristolochia pub era R.Br, a small plant generally found in shady palces between rocks and weeds. At Samford, females of E. cressida were frequently observed laying eggs on A. elegans. Numerous eggs, which are bright orange and conspicuous, were collected and transferred to the insectary. The resulting larvae were released on A. elegans, which they accepted more readily than did the larvae of T. priamus, but no specimens survived beyond the third instar.
3. Papilio demoleus sthenelus MacLeay is the only papilionid which occurs in the dry inland areas of Australia, where Edwards (1948, 1955) recorded Psoralea (Leguminosae) as its natural hostplant. In some years migratory flights reach the coastal areas, and in Southeastern Queensland P. demoleus is found every year, although sometimes locally and in small numbers. In March 1960 eggs and larvae were found on a young Citrus plant near Samford and transferred to the laboratory. The larvae continued to feed normally on leaves from the same plant until they reached the last instar. From then on they sat motionless for days, refusing to feed, and finally died. The larvae which hatched from the eggs showed a similar behaviour and died in the last instar. When inspecting the citrus plants growing in the immediate vicinity of the tree from which the specimens had been collected, a small number of fourth instar larvae of P. demoleus were found but left undisturbed. Frequent inspections showed that these larvae also died in their final instar.
In the first week of April, numerous P. demoleus butterflies were seen at Samford, flying in and around a swampy paddock, which was overgrown with tall grasses and weeds. Female butterflies were seen ovipositing on a small weed, identified as Psoralea tenax (Leguminosae). A search resulted in 25 eggs and 20 larvae in various instars which were transferred to the insectary. Ten larvae which were reared on Psoralea, grew rapidly and pupated. The other ten larvae were reared on Citrus, accepted after a day of restlessness, but all died before pupation.
From the eggs, 24 larvae hatched, which were divided into two feeding groups; 12 were given Citrus and 12 Psoralea tenax. The Citrus feeders were slow growers; while these were still in the first instar, the control specimens on Psoralea had reached the third instar. No Citrus feeders lived beyond the second instar, by which time some Psoralea feeders
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Journal of the Lepidopterists' Society
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started to pupate. Neither eggs nor larvae of P. demoleus were found on Citrus plants growing in the immediate vicinity of the paddock. The specimens collecited on Citrus as described were found in a much drier and hilly area where it is unlikely that Psoralea occurred. It was noticed that larvae which lived on Citrus had a bright orange groundcolour in the fourth and fifth ins tars with distinct black markings, while most Psoralea feeders showed a green to pale yellow groundcolour with reduced black markings.
4. Euphea eichhorni Staudinger is common in Northeastern Queensland and it is supposed that its hostplants belong to the Apocynacese or the Moraceae. On several occasions, females were observed in the garden around the laboratory at Ingham while laying eggs on Frangipani (Plumeria acutifolia, Apocynaceae). When damaged, this plant produces a milky sap and in this respect resembles the plants which would be the normal hostplants. Numerous eggs were seen but no larvae found, while no plants showed any damage caused by feeding. When again, a female was observed ovipositing on Frangipani, 12 eggs were collected and transferred to a petri-dish. The larvae hatched after five days and were given young leaves of the same plant from which they were collected. However, after nibbling at the leaves they refused to feed and died during the second day after hatching.
Discussion
Observations such as described above suggest that ovipositing butterflies are not infrequently deceived by attractive stimuli from abnormal hosts, to such an extent that eggs may be laid on plants which are, in fact, toxic to the resulting larvae. In the case of Aristolochia species, this is presumably due to the close relationship of the normal host to the toxic plant. It is significant that, in the cases described, the toxic species (A. elegans) is an introduced plant, and there has apparently been insufficient time as yet for the butterfly to become adapted, i.e., either to develop the ability to feed on it, or to discriminate during oviposition. It is perhaps also significant, that in the case of T. priamus richmondiuSy larva?, from the area where the introduced plant does not seem to occur, died in the first instar. Those from the area where both species of Aristolochia occurred, did survive until the third instar, suggesting that some degree of adaptation may be evolving.
In the case of P. demoleus, its reported hostplants in countries other than Australia are species of Rutaceae. However, Edwards (1948 and 1956) reported that in the Mitchell area (more than 300 miles west of Brisbane), P. demoleus sthenelus feeds on Psoralea patens and P.
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tenax and that he was not able to rear it on Citrus. Hely (1958), replying to Edwards's paper, than stated that in 1943 and 1950 he had found larvae and pupae of P. demoleus on young citrus plants in the nursery of the Gosford Experimental Station, Narara, N. S. W. and that he had succeeded in rearing these specimens on Citrus. He also reported that in 1953 Mosse Robinson had observed a female of P. demoleus ovipositing on Psoralea affinis in a garden at Gosford and successfully reared specimens on that host plant; also that he had collected and successfully reared larvae on Citrus. Previously, Waterhouse (1932) had written "during 1922 on the Richmond River it occurred in thousands; if a branch of an orange-tree was held up by the hand, the females would lay their eggs on it". He also mentioned Salvia as a foodplant, as did Rainbow (1907), but gave no details.
A foodplant of P. demoleus in Ceylon and India, mentioned by Moore (1880), Seitz (1927) and Woodhouse (1950), is Glycosmis pentaphylla, a rutaceous weed which also occurs in Northern and Northeastern Australia, where however, as far as is known, larvae of P. demoleus sthenelus have never been found on this host.
The evidence available suggests therefore that P. demoleus may have developed separate local strains that differ in their association with Citrus: in Queensland rarely laying on and unable to develop on Citrus plants; in N. S. W. evidently accepting Citrus with complete success. It should be noted that, as in the case of Aristolochia elegans, plants of the genus Citrus are not native to Australia and it is possible that in this country P. demoleus became adapted to native plants of the genus Psoralea. With the introduction of Citrus plants, which are the normal hosts in other countries, it may have become possible, either for local populations of P. demoleus to revert to the ancestral feeding habit, or to develop Citrus feeding strains from eventual immigrant butterflies. No explanation can be seen, however, for the original selection of the quite unrelated Psoralea as a hostplant, when native species of rutaceous plants are available. In fact, as far as is known, there are no other records of a leguminous plant as the normal host of a papilionid.
In Australia several Euplcea species have been reported from host-plants belonging to the Apocynaceae and the Asclepiadaceae; members of these families generally have a milky sap.
Frangipani (Plumeria acutijolia, Apocynaceae) is an introduced plant and is common in parks and gardens. As far as is known, no damage caused by Euplcea larvae has ever been recorded on this plant. The normal host of E. eichhorni has not been described but probably belongs to one of the two above families. Once again we find that the abnormal, toxic host is an introduced plant, related to what is probably the normal
1962
Journal of the Lepidopterists' Society
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host, and presumably resembling it in the stimuli which attract ovipositing females. In this case however, there is no evidence to suggest that any adaptation to this new host has yet occurred.
Summary
Females of four species of Australian Lepidoptera were observed ovipositing frequently on introduced plants on which the resulting larvse were unable to survive because of toxic effects. These species were Troides priamus richmondius, Eurycus cressida cressida, Papilio demoleus sthenelus, and Euplcea eichhorni. In most cases the toxic host is closely related to the normal native host plant, except in the case of P. demoleus sthenelus, ovipositing on Citrus, its normal host in other countries.
Acknowledgments
The author expresses his sincere gratitude to Dr. D. H. Colless of the Division of Entomology, C. S. I. R. O., Canberra, for his advice and assistance in the preparation of this manuscript.
The writer is also grateful to Mr. M. Gray, of the Division of Plant Industry, C. S. I. R. O., for identifying specimens of the host plants.
References
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