The world’s insects are in trouble – if we start using pesticides to protect plants rather than killing insects it could make a big difference, says Théotime Colin and Andrew B. Barron

Environment


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2 June 2021

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Michelle D’urbano

INSECTS are disappearing. The world has 25 per cent fewer terrestrial insects now than in 1990. This includes those we rely on to pollinate our crops and clean our rivers. If we don’t solve this problem very soon, some species will disappear.

There are many causes for the insect decline, but insecticides are a major part of the problem. Those used today are longer lasting and up to 10,000 times more toxic than some that were banned in the 1970s. Adding to the problem is that these pesticides are now applied to crops prophylactically and used whether pests are present or not.

Overall, the amount of pesticide applied to the land is decreasing, but this is a grossly misleading statistic. A recent paper found that, between 2005 and 2015, there was a 40 per cent reduction in the amount of pesticide applied to crops measured by weight. But because modern insecticides are so much more toxic, the global toxicity of treated land to pollinating insects has more than doubled in the same period (Science, doi.org/f5vp).

Governments and regulating agencies are aware of the problem, and some parts of the world have moved to ban the use of certain insecticides outdoors in an attempt to help bees survive. But the pesticides used instead are just as toxic.

One often-touted approach is to use pesticide-free pest control methods. These varied techniques are gathered under the name of integrated pest management (IPM) and have been around for decades. They offer effective crop protection and include methods such as crop rotation and the use of natural predators. But their adoption has been incredibly slow, because spraying pesticides is viewed as an easier option. As a result, IPM methods are unfortunately seldom used today.

Neither changing insecticides nor shifting to IPM is a quick fix. We argue instead that we need a subtle shift in focus, away from killing pests and towards protecting crops.

Currently, products are developed and marketed to kill pest insects immediately. This has become the goal of crop treatments, and the death of the insect is considered the proof that a treatment works. But the real goal of pesticide use isn’t to wipe out insects, it is just to protect crops to secure food production.

We have found that using just a fraction of the concentrations applied today stops insects feeding on crops. At these reduced concentrations, there would be a lot less insecticide leaching into the environment, so less harm to beneficial insects. This low dose is the equivalent of an anti-mosquito spray: it repels mosquitoes so they don’t bite you. Whether the mosquito is alive or not doesn’t matter, either way you have received protection.

Similarly, we don’t need to kill all pest insects in a crop: we just need to reduce the population enough to ensure that it causes no important economic damage. Farmers know that a handful of insects don’t cause problems, it is when they reproduce that trouble comes. We have found that much less insecticide is needed to prevent insects from reproducing than is needed to kill them.

We have also discovered that crops are inadvertently treated too many times. Often, they are first treated with fungicides that also happen to be toxic to insects. Treating them again with an insecticide is like killing one bird with two stones.

By using the minimal dose we need to protect crops, we could reduce the amount of insecticide to a fraction of what is used today. Farmers would benefit from these changes. They would spend less money on pesticides and improve crop production by keeping healthy pollinator insects about.

Reducing insecticide doses won’t solve the insect decline problem, but it is a move that could win us time to make food production more sustainable and reconcile farmlands and the natural ecosystems we crucially depend on. And that will allow insects to recover.

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