Readers’ wildlife photos

Today we have another informative contribution from Athayde Tonhasca Júnior; his narrative is indented and the photos (credited) can be enlarged by clicking on them.

Cognitive dissonances: chocolate vs midges, wine vs wasps

Theobroma cacao. Named after the Greek theos (god) and broma (food), the cacao plant is, as any chocoholic would agree, the’ food of the gods’.

Cacao beans made their way to Europe as medicine: the cocoa drink cacahuatl (bitter water) of the Maya and Aztec peoples was considered a palliative to abdominal pains and other illnesses. When someone thought of sweetening the paste made of cacao beans, chocolate left the apothecary’s shelf for the kitchen and then for the factories. Joseph Fry – who created the first chocolate bar and Easter egg – Henri Nestlé, Rodolphe Lindt, Milton Hershey and many others helped build an ever-growing industry. Today, Americans and Europeans consume more than US$100 billion worth of chocolate annually, produced mostly in West Africa.

Fig. 1. A possible Maya lord sits before a container of frothed chocolate. Wikipedia (image in the public domain).

Not many people know that chocolate production, and by extension the livelihoods of countless small-scale cacao farmers in the developing world, depend on the finicky pollination requirements of the cacao flower.

Cacao blooming occurs simultaneously and extensively: in a short time, the plant’s trunk and main branches are covered with thousands of flowers. This feature is known as cauliflory.

Fig. 2. Cacao flowers sprouting from a tree trunk © Kurt Stueber, Wikimedia Commons.

The flowers cannot self-fertilize, so they are entirely dependent on pollinators. But the blossoms are small, have a convoluted hooded shape and face downwards. So bees, hoverflies and other common flower visitors do not bother with them, or just can’t reach their pollen and nectar. If flowers are not fertilized, they abscise (drop off) the next day: only 1 to 10% of all flowers develop into a fruit.

Fig. 3. A cacao flower © Crista Castellanos, Wikimedia Commons.

Fig. 4. Cacao beans in a pod © Aude, Wikipedia.

This apparently inefficient reproductive apparatus makes no sense until we are reminded that the cacao plant originated from the rainforests of Central and South America. These are hot, dense, dark and moist environments, choked with rotten wood and decomposing leaf litter. This type of habitat is hostile to many sun-loving pollinators, but it’s perfect for one group of insects – biting midges.

These are ceratopogonid midges (family Ceratopogonidae), of which the 1,000 or so species from the genus Forcipomyia are particularly important for our story. Male and female flies spend most of the day hidden in the forest’s shady spots, coming out in swarms of enormous numbers in the early morning and late afternoon to collect nectar from cacao flowers. Adults live for about a week, but there are about 12 generations per year. Thanks to their small size – 1 to 3 mm in length – midges can squeeze their way into the pollen-producing anthers of the unreceptive cacao flowers. For pollination to happen at a satisfactory scale, all it takes is a few pollen grains attached to the thoracic hairs of a fraction of the millions of pesky flies.

Fig. 5. A male Forcipomyia sp. midge © Christophe Quintin, CC BY-NC 2.0

Traditionally, cacao has been grown in shaded areas intercropped with native trees that were spared when the forest was cleared for cultivation. Today, cacao often grows in open plantations, which do not have the damp and shady conditions required by biting midge larvae. Also, within commercial plantations, the time of peak flower abundance may be out of synch with the peak of midge populations. The loss of midge habitat may explain in part why cocoa production has been decreasing, even though demand has increased annually.

However limited our knowledge about midge pollination, it’s far more than what we know about other potential candidates: aphids and thrips. In some situations, these may pollinate more cacao flowers than midges. Whatever the relative contribution of these insects, it’s evident that the cacao plant is a peculiar customer; it has no use for the traditional pollinators (bees, moths, bats or birds).

Fig. 6. Advertisement for Cadbury’s cocoa in The Graphic, 1885. Wikipedia (image in the public domain).

I saw a wasp upon a wall
And did not like his face at all:
And so the creature had no time
To wonder whether he liked mine.

‘Plain Murder’, by A.G. Prys-Jones

As you undergo an epiphany about midges, you may find room to accommodate wasps in your positive thoughts.

Social wasps (yellowjackets in America) of the genera Vespula such as the common (V. vulgaris) and the German wasp (V. germanica) surely are contenders for the accolade of most hated and feared insects. That’s a shame, because there is more to them than being flying thugs.

Adult wasps feed mostly on high-energy sugars and carbohydrates from foods such as nectar and fruit. They are not covered with fuzzy hair, so are much less efficient pollinators than bees. Even so, wasps are thought to be the main pollinators of ivy (Hedera spp.), which flowers late in the year, a time when the number of bees diminishes. Because of their high energy content, ivy fruits are important for many farmland and garden birds, so wasps contribute to their food supply.

Fig. 7. A German wasp © Richard Bartz, Wikimedia Commons.

But no sugar will do for the larvae – they need protein. Which is provided by the adults in the form of soft-bodied invertebrates such as caterpillars, flies, spiders and beetle larvae. Researchers in New Zealand (Harris, 1991. N. Zealand J. Zool. 18: 159–169; Brock et al., 2021. Biol. Rev. 96: 1645–1675) estimated that wasps capture ~0.8 to 4.8 million prey items per hectare per season (1.4 to 8.1 kg of prey/ha), which is equivalent to what is taken by all insectivorous birds in the same area. The figures elsewhere are likely to be lower, but nonetheless it is evident that wasps are voracious predators, and thus gardeners’ and farmers’ allies.

Fig. 8. A common wasp captures a horsefly © Robert Goossens, Wikimedia Commons.

Wasps may spoil your picnic, but without them, your hamper could have been deprived of bread, beer and wine.

Yeasts – especially Saccharomyces cerevisiae – have been fundamental to baking, brewing and winemaking throughout human history.

Fig. 9. Marmite, a black goo made from yeast extract (a by-product of beer brewing). This quintessentially British product was discovered by the German scientist Justus Liebig (1803-1873) of Liebig’s Law of the Minimum fame © WestportWiki, Wikimedia Commons.

In nature, yeast cells are found primarily on ripe fruits during the summer months. Since S. cerevisiae is not airborne, it must rely on vectors to move from plant to plant. For years it has been assumed that birds or bees were responsible for transporting yeast cells, but nobody could explain how they survived the winter. Italian and French researchers (Stefanini et al., 2012. PNAS 109: 13398–13403) suspected that wasps were involved because they feed on yeast-harbouring grapes, and their nests are hibernation havens for microorganisms.

The research team analysed samples from vineyards around Italy to find several species and hundreds of strains of yeast in the wasps’ guts. Some were related to wine strains of S. cerevisiae, others were similar to bread strains. Also, yeasts persisted through the winter in the insects’ guts, and were transferred to the larvae via the food regurgitated by the queen. And there’s more: S. cerevisiae produced spores, germinated and mated inside wasps’ guts (Stefanini et al., 2016. PNAS 113: 2247–2251). The results demonstrated a strong connection between social wasps and the diversity and abundance of yeasts.

Fig. 10. Wasps breaking and eating grape berries © Thomas Quine, Wikimedia Commons.

Wasps may be a nuisance now and then, but possible clashes with us are easily avoided. They are not aggressive outside the nest; when they hover persistently over your bottle of lemonade or sandwich, they are interested only in the food and will not deliberately attack you. If a wasp flies towards your food, wait for it to go away; flapping your arms increases the chances of entrapping it, which could end up in tears. However, wasps will defend their nest aggressively if disturbed or threatened. If you find yourself near a nest, retreat without producing much vibration or noise.

So next time someone asks what’s the point of wasps, you can say they are fascinating creatures with complex social organisation; they help control pests, and your wine or beer may depend on them. So there.

Fig. 11. A Michelangelo moment thanks to humble wasps.