From chocolate to mangoes, chillies and onions, the humble fly is key to many of our favourite food dishes. Now that many of you have bitten into that chocolate egg and bunny, say a thank-you to the midge and hover fly. Hover flies are second only to bees in their value as commercial pollinators.
The pollinating role of flies is hugely important for the general health of a range of ecosystems, including agricultural ones. Of the 150 families of flies have been shown to feed from flowers and therefore in principle transmit pollen from one plant to another. It’s not just the number of species that qualifies flies as important pollinators but also their distribution. Flies are ubiquitous—they are everywhere – even in high altitude areas. A whole variety of them are found in different regions, including many hover flies from the family Syrphidae.
Hover flies are exceptionally common, distributed everywhere and very species-rich, with more than 6,000 species described globally to date. They are considered to be the most important of dipteran (two-winged) pollinators although this may change as knowledge of fly biology increases. As their name suggests, they hover.
The economic worth of all insect pollinators of cultivated crops equates to 35 per cent of global crop-based food production. Flies form a high component of that figure and they are key pollinators for many crops including cocoa, mango, chilli pepper, black pepper, carrot, fennel and onion.
Flies and chocolate
Cocoa beans come from the fruit of the rainforest tree, Theobroma cacao. Thought to originate from the upper Amazon and cultivated by the Mayans and Aztecs for thousands of years, cocoa trees are now grown around the globe within 20 degrees north or south of the equator. In Australia, the line passes near Bowen in Queensland’s far north.
The botanical name Theobroma is derived from the Greek for ‘food of the gods’. Cocoa trees are rainforest understorey plants, reaching around 5m to 8m with broad, lush leaves. The flowers are produced in small clusters directly on the bark of the trunk and branches. While each tree can produce more than 100,000 flowers, only about 0.1pc turn into fruit, called pods, that also project straight from the bark.
The pods take about five months to ripen, developing to the size of an eggplant. It takes between 15 and 35 fruits to harvest 1kg of beans. The beans are fermented for several days to develop the chocolate flavours, then dried and roasted to intensify aroma and taste.
The pollinators are tiny flies. This plant species has so complex a reproductive structure, only one group of very small flies, amusingly known as ‘No See Ums’, can pollinate it. This group, from the Forcipomyia genus of the family Ceratopogonidae, are, along with the rest of the family, known as the biting midges.
The female adults of many biting midges have very painful and sometimes fatal bites due to some of the diseases they can transmit. But without these minute flies, many people would consider that life is no longer worth living. Cacao producers are very worried about the ongoing supply of their ‘miracle’ substance.
A major challenge limited cocoa production around the world is that an estimated 40pc of crops are lost to pests and fungal disease. Urgent research is underway to breed disease-resistant varieties.
Thanks to: ‘The Sweetest Fruit’; The Weekend Australian magazine, April 8-9, 2023 (Helen Young); and ‘The Secret Life of Flies’; Science Friday, Dec 29, 2017 (Erica McAlister).