| Xanthopan | |
|---|---|
 | |
| Natural History Museum of London | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Lepidoptera |
| Family: | Sphingidae |
| Tribe: | Sphingini |
| Genus: | Xanthopan Rothschild &Jordan, 1903 |
| Species: | X. morganii |
| Binomial name | |
| Xanthopan morganii (Walker, 1856) | |
| Synonyms | |
| |
Xanthopan is amonotypic genus of sphinx moth, withXanthopan morganii (often misspelled as "morgani"),[1] commonly calledMorgan's sphinx moth, as its sole species. It is a very largesphinx moth from Southern Africa (Zimbabwe,Zambia,Malawi) andMadagascar. Little is known about its biology, though the adults have been found to visitorchids and are one of the main pollinators of several of the Madagascar endemic baobab (Adansonia) species,[2][3]Adansonia perrieri or Perrier's baobab.
In January 1862 while researchinginsect pollination of orchids,Charles Darwin received a package of orchids from the distinguished horticulturistJames Bateman, and in a follow-up letter with a second package Bateman's sonRobert confirmed the names of the specimens, includingAngraecum sesquipedale from Madagascar.[5][6] Darwin was surprised at the defining characteristic of this species: the "astonishing length" of the whip-like greenspur forming thenectary of each flower, and remarked toJoseph Hooker "I have just received such a Box full from Mr Bateman with the astoundingAngræcum sesquipedalia with a nectary a foot long—Good Heavens what insect can suck it"[?][7] The spur of the flower is 20–35 cm (7.9–13.8 in) from its tip to the tip of the flower's lip. The name "sesquipedale" is Latin for "one and a half feet", referring to the spur length.
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From his observations and experiments with pushing a probe into the spur of the flower, Darwin surmised in his 1862 bookFertilisation of Orchids that there must be a pollinator moth with aproboscis long enough to reach the nectar at the end of the spur.[8] In its attempt to get the nectar at the end of the spur the moth would get pollen rubbed off on its head. The next orchid it visited would then be pollinated in the same manner.[4]
In 1867Alfred Russel Wallace published an article in which he supported Darwin's hypothesis, remarking that the Africansphinx mothXanthopan morganii (then known asMacrosila morganii) had a proboscis almost long enough to reach the bottom of the spur. In a footnote to this article Wallace wrote "That such a moth exists in Madagascar may be safely predicted; and naturalists who visit that island should search for it with as much confidence as astronomers searched for the planet Neptune,—and they will be equally successful!"[9]
Subsequently, the sphingid expertsWalter Rothschild andKarl Jordan received one male and one female specimen ofXanthopan morganii (commonly called Morgan's sphinx moth) with an especially long proboscis, collected on Madagascar byCharles Oberthür andPaul Mabille. Since Wallace predicted that the mystery pollinator would turn out to be a sphinx moth, rather than simply a large moth as Darwin had suggested, the Madagascan form was named subspeciespraedicta by Walter Rothschild and Karl Jordan, in honour of Wallace's (not Darwin's) prediction. Darwin's earlier, but less specific, prediction was not even mentioned by them.[10][11]
The Madagascan subspecies is known as Wallace's sphinx moth and it differs from the African form by having a pink, rather than white, breast and abdomen and a black apical line on the forewing, which is broader than in mainland specimens. Molecular clock models using either rate- or fossil-based calibrations imply that the Madagascan subspeciesX. morganii praedicta and the African subspeciesX. morganiimorganii diverged 7.4 ± 2.8 Mya, which overlaps the divergence ofA. sesquipedale from its sister,A. sororium, namely 7.5 ± 5.2 Mya.[12] Since both these orchids have extremely long spurs, long spurs likely existed before that and were exploited by long-tongued moths similar toXanthopan morganii praedicta. The long geological separation of the subspeciesmorganii andpraedicta matches their morphological differences in the colour of breast and abdomen. In 2021 it was determined that Wallace's sphinx moth was so distinct that it is in fact asister species;Xanthopan praedicta.[13]
Morgan's sphinx moth approaches a flower to ascertain by scent whether or not it is the correct orchid species. Then the moth backs up over a foot and unrolls its proboscis, then flies forward, inserting it into the orchid's spur.[14]
The larvae feed onAnnona senegalensis,Hexalobus crispiflorus,Uvaria,Ibaria andXylopia species.[15]
Long tongued sphinx moths are vulnerable to predation by bats when foraging. Some species, such as Wallace's sphinx moth (X. m. praedicta), are capable of producing ultrasonic sounds to deter bat predation. In Wallace's sphinx moth, this occurs by using rapid ultrasonic clicks to jam bat sonar by overwhelming the processing of the bat's echoes. However, only males are capable of doing so. Wallace's sphinx moth does not exhibit this only when exposed to bat sonar, but also when physically handled. The sound production of Wallace's sphinx moth is exceptional amongst sphinx moths. In sphinx moths, the required duty cycle to jam bat sonar is around 20%. The duty cycle of Wallace's sphinx moth is around 29%, amongst the highest of all sphinx moth species. Modulation cycle duration ranks amongst the highest in sphinx moths.[16]
The frequency range is also remarkably broadband for a sphinx moth, and has one of the lowest dominant frequencies of any sphinx moth, meaning there is potential for it to deter predators other than bats, such as omnivorous lemurs. For the same reason, Wallace's sphinx moth's anti-predator defence can actually be heard by humans.[16]