Flies generally get a bad rap. People associate them with dirt, disease and death. “No one except entomologists really likes flies,” Finch says. Yet there’s good reason why we should cherish, encourage, even nurture them: Our future food supply could depend on it. The past few years have seen growing recognition that flies make up a large proportion of wild pollinators — but also that we know little about that side of their lives. Which sorts of fly pollinate what? How effective are they at delivering pollen where it’s needed? Which flies might we harness to boost future harvests — and how to go about it? With insect populations plummeting and honeybees under pressure from multiple threats, including varroa mites and colony collapse disorder, entomologists and pollination specialists are urgently trying to get some answers.
Animals are responsible for pollinating around 76 percent of crop plants, including a large number of globally important ones. Birds, bats and other small mammals do their bit, but insects do much more — pollinating flowers of many fruits, vegetables and nuts, from almonds to avocados, mangoes and melons, cocoa and coconuts, as well as crops grown to provide seed for future vegetable harvests. In a recent analysis for the Annual Review of Entomology, Australia-based biologist Romina Rader and colleagues from Australia, New Zealand and the US calculated that the world’s 105 most widely planted food crops that benefit from insect pollination are worth some $800 billion a year.
Bees, especially honeybees, get most of the credit, but overlooked and underappreciated is a vast army of beetles, butterflies, moths, ants, flies and more. In Rader’s analysis, only a handful of crops were visited exclusively by bees; most were visited by both bees and other insects. She and her colleagues assessed the contribution of each type of insect and found that flies were the most important pollinators after bees, visiting 72 percent of the 105 crops.
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Making fields and orchards more fly-friendly won’t always be enough. With that in mind, researchers round the world are trying to identify flies that can be reared commercially and released where and when their services are needed. But where to start? The vast majority of pollination studies have focused on bees, and although many species of flies have been reported visiting crops, in most cases little is known about how good they are at transporting pollen, let alone whether their visits translate into more fruit and vegetables.
That’s beginning to change. Scattered studies have logged how often flies visit flowers, counted the pollen grains stuck to their bodies and recorded crop yields, and found that some flies give bees a run for their money — and in some cases, outdo them. Researchers studying avocados in Mexico, for instance, found that the large green blowfly Chrysomya megacephala (aka the oriental latrine fly) visited more flowers in a given time than bees and carried pollen grains on parts of the body that would contact the stigma of the next avocado flower it visited. Studies in Israel, Malaysia and India all suggest that blowflies are effective at pollinating mangoes, while trials in the US and New Zealand showed that the European blue blowfly (Calliphora vicina) produced as good a yield of leek and carrot seed as bees.
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