Today we have another photo-and-story piece from Athayde Tonhasca Júnior. His narrative is indented, and you can enlarge the photos by clicking on them:
Flavour of the month
Many things can be ‘plain vanilla’, but vanilla is not one of them. This spice comprises a complex mixture of vanillin and other organic compounds that produce its distinctive flavour and aroma. The main source of vanilla, the flat-leaved vanilla orchid (Vanilla planifolia), is native to Central and South America but grown commercially in tropical areas around the world; Madagascar is by far the largest producer, followed by Indonesia.
A flat-leaved vanilla orchid © Malcolm Manners, Wikimedia Commons:
Vanillin is found in the orchid’s ‘beans’ (botanically speaking, its fruits), and it’s not easy to get. The vanilla orchid grows as a vine that can extend for 20 to 50 metres, so it needs supporting structures to spread out. In its native range, the vanilla flower is pollinated by bees; elsewhere, it is hand-pollinated (you can watch how this is done). The operation has to be quick because a flower remains receptive for about 24 hours. If not pollinated, it wilts and falls to the ground. The beans take six to nine months to mature; when ready, they are hand-picked, dipped in hot water and dried for up to a month. So it’s not surprising that such a labour-intensive crop doesn’t come cheap: as spices go, only saffron costs more by unit of weight.
So how come your run-of-the-mill vanilla ice-cream or cake is not particularly dear? Because about 99% of all vanilla products (food, beverages, cosmetics and pharmaceuticals) are flavoured with synthetic vanillin, which can be obtained from wood pulp, clove oil, coal tar and other petrochemicals, and it’s about 20 times cheaper than natural vanilla. Chefs, bakers and food buffs debate the organoleptic differences between natural and synthetic vanilla. Whatever their verdict, the food industry is under growing pressure to reduce artificial flavours from their products, so production of natural vanilla remains strong and tends to increase.
The growing value of natural vanilla is promising to small farmers in Madagascar and other developing countries, but there are clouds on the horizon. Almost all natural vanilla comes from a single species cultivated as a monoculture in a few areas around the globe, and all plants are obtained by cloning (cuttings). These distribution and propagation patterns promote genetic uniformity, which is a risk to vanilla production. A simplified and impoverished genetic base makes the crop vulnerable to diseases and pests, which are similar threats to those hanging over the genetically homogeneous bananas available to European and American consumers.
One way to reduce these risks is in-situ conservation, that is, the protection of flat-leaved vanilla orchids in their places of origin. These areas are natural gene banks, potential sources of genetic material that could be incorporated into crops to help them adjust to new environmental stresses. And here, bees may have a lot to contribute.
In the wild, flat-leaved vanilla orchids grow in isolation deep inside mature forests, climbing from one tree to another. When plants reach a certain size, they produce only a handful of flowers. A pollinator needs special skills to locate a flower in the chaotic, crowded environment of a tropical jungle. This is a job for orchid or euglossine bees (tribe Euglossini). Females gather pollen and nectar like any ordinary bee, but males spend a great deal of their time collecting volatile compounds, primarily from orchids; they can fly for dozens of kilometres in pursuit of the right scent. Males store a variety of these chemicals, and the resulting aromatic bouquet advertises their prowess to females. Many orchids take advantage of this perfume obsession: they are especially adapted to transferring pollinia (pollen packets) to the bodies of visiting male orchid bees.
An orchid normally hidden in the forest canopy was brought down and exposed by a tree fall © Tatiana Gerus, Wikimedia Commons:
A male Euglossa analis © The Packer Lab, Wikimedia Commons:
Orchid bees are the main, or possibly the only, pollinators of the flat-leaved vanilla orchid, although we have only sketchy details about specific species. These bees play another role in the orchid’s life, one that has been recognised only recently: as seed dispersers.
Orchid bees collecting scents from mature fruits of flat-leaved vanilla orchids. A: Euglossa sp. B: Eulaema sp. C: Exaerete sp. © M.A. Lozano Rodríguez (Rodríguez et al., 2022):
Seed dispersal is as important as pollination. By having its seeds spread out over large distances, a plant does not have to compete with its seedlings. Dispersed offspring also has a better chance of escaping predators, diseases or environmental misadventures that may befall the parent plant. Herbivores play a big part in dispersal: the seeds in the fruits they eat will end up in a steamy, fertilised pile somewhere. But mammals and birds are not tempted by most orchids because their fruits are not particularly nutritious. It makes no difference for most orchids; their seeds are easily uplifted and dispersed by the wind: for some species, 3 million seeds weigh as little as 1 g.
But things are different for Vanilla spp. and a few other orchid genera: they produce fleshy fruit whose seeds are protected by a hardened coat and not easily carried by the wind. These characteristics suggest zoochory (seed dispersal by animals), and indeed rodents and marsupials eat the fruits of flat-leaved vanilla orchids, later passing the seeds. Karremans et al. (2023) discovered that some male orchid bees and female stingless bees (tribe Meliponini) join the feast: they take seeds away when the fruits split open naturally. So the flat-leaved vanilla orchid is likely to be part of a select group of plants with mellitochorous seeds, i.e., dispersed by bees. Mellitochory is not common, but this could reflect our lack of knowledge more than rarity of the phenomenon. Most recorded cases involve seeds hitching a ride when stingless bees collect resin or other nest-building material. Later these seeds fall off or are chucked out of the bees’ nests, germinating on the ground.
(a) A Trigona carbonaria stingless bee taking resin from a cadaghi (Corymbia torelliana) fruit in Australia (scale bar = 1.6 mm). (c) T. carbonaria carrying resin and seed of C. torelliana (scale bar = 1.5 mm). Photographs by Robert B. Luttrell © Wallace et al., 2007.
To summarise: there’s a global craving for natural vanilla, which is extracted mostly from one species of orchid whose populations are vulnerable to genetic homogeneity. Protecting native orchid habitats would allow bees to give a hand by pollinating flowers and dispersing their seeds, thus helping safeguard commercial flat-leaved vanilla against future vicissitudes. This intricate tale is anything but plain vanilla.