Ian Kitching, together with colleagues at the University of California, National University of Singapore and the University of Erlangen, Germany, has published a review paper charting the history of Charles Darwin’s prediction of coevolution between a long-spurred orchid, Angraecum sesquipedale, and a long-tongued hawkmoth, Xanthopan morganii praedicta, from Darwin’s first observations in 1862 to the final demonstration of successful pollination in the wild in 2004.
Darwin wrote in his 1862 work On the various contrivances by which British and foreign orchids are fertilised by insects, and on the good effects of intercrossing:
I fear that the reader will be wearied, but I must say a few words on the Angræcum sesquipedale, of which the large six-rayed flowers, like stars formed of snow-white wax, have excited the admiration of travellers in Madagascar. A whip-like green nectary of astonishing length hangs down beneath the labellum. In several flowers sent me by Mr. Bateman I found the nectaries eleven and a half inches long, with only the lower inch and a half filled with very sweet nectar. What can be the use, it may be asked, of a nectary of such disproportional length? We shall, I think, see that the fertilisation of the plant depends on this length and on nectar being contained only within the lower and attenuated extremity. It is, however, surprising that any insect should be able to reach the nectar: our English sphinxes have probosces as long as their bodies: but in Madagascar there must be moths with probosces capable of extension to a length of between ten and eleven inches!
A moth with such a long proboscis, Xanthopan morganii praedicta, was not described until 41 years after the publication of this book, and it was not observed to visit Angraecum until 1992, with further work to prove pollination since then. Ian and colleagues discuss issues of co-evolution and predation in this excellent paper.
Arditti, J., Elliott, J., Kitching, I.J. & Wasserthal, L.T. 2012. ‘Good Heavens what insect can suck it’ – Charles Darwin, Angraecum sesquipedale and Xanthopan morganii praedicta. Botanical Journal of the Linnean Society 169: 403-432.