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An extensive study looks to quantify the extinction of insects around the world, and finds agriculture to be a driving factor in declining populations.

The world is undergoing a dramatic loss of animal species, and perhaps no class is in greater peril than insects. Though small, insects are incredibly important animals. Not only are they food for other animals in the wild, but their pollination services are necessary for the survival of many plant species. Without insect pollinators, humans would likely lose a great deal of our own food supply.

Understanding the extent to which insects are declining, as well as the causes of their decline, is essential to preventing their extinction – and therefore that of untold numbers of other animals. This meta-analysis looks at existing long-term studies of insect populations, most of which are taken from North America and Europe. For the purposes of this analysis, the researchers looked at studies of single species, studies that looked at a period of less than 10 years, and studies of invasive species or pest outbreaks; Studies that did not deal in quantitative data were excluded. In all, 73 studies were analyzed.

The information gathered is both jarring and disturbing. Around half of all Lepidoptera (butterfly and moth) and Coleoptera (beetle) species for which long-term studies exist are declining faster than the average rate. One in six bee species has gone regionally extinct. The largest loss that the researchers found was in Mediterranean dung beetles, of which 60% of species are in decline. Dung beetles are important for disposal of dead and decaying matter, and reduce the populations of many pests. Over half of ladybug species for which studies were available were found to be in severe decline.

All-told, 40% of insect species studied were found to be in decline and at risk of extinction, double the rate for vertebrates. The authors stress that their research is incomplete. There are many groups of insects, like hoverflies, for which not enough information is available to make accurate judgments. In addition, studies from Asia, Africa, and South America are lacking.

The cause of insect decline varies between species. The most commonly-cited reason for a species’ decline in the studies analyzed was habitat change, composing about half of all given reasons. Agricultural development is the most common habitat change listed in the analysis, followed by urbanization and deforestation.

Intensive, industrialized agriculture is associated with a sharp drop in insect species. Shifting to monoculture crops spelled doom for many specialized pollinators, as their food source was eliminated. The removal of hedgerows eliminated the habitat of many specialist ground beetles, and clearing of trees inhibited reproduction of many moth species. Modification of rivers and streams to better irrigate cropland has made them less livable for many aquatic insects, like dragonflies. Urbanization generally eliminates specialist species that cannot adapt to human-centered environments, favoring generalist species like the housefly and American cockroach. However, green space in cities can be modified to become refuge for specialist species.

Pollution is listed as the second major cause of insect declines, especially the overuse of agricultural pesticides. Insecticides and fungicides pose a direct threat to insects, especially neonicotinoid, pyrethroid, and fipronil types. Herbicides also pose a major threat through the elimination of wild plants that many insect species depend upon. Overall, widespread and indiscriminate pesticide use is one of the most significant causes of insect depopulation. Synthetic fertilizers are also deserving of some blame, especially for the decline of specialist pollinators, many of which are heavily dependent on surface nitrogen levels. These synthetic fertilizers also contribute to the decline of aquatic insects through reducing the oxygen content of surface water. Industrial chemicals are also known to be responsible for the decline of some aquatic insects though their general impact is less well-understood.

Invasive species are known to be responsible for many extinctions, both regional and general. However, the authors do not believe them to be nearly as serious a threat as human activity. Furthermore, introducing certain species to use as pest control – such as ladybugs to control aphids – can reduce reliance on synthetic pesticides, which is necessary to prevent the decline of other species. Parasites and diseases have also been implicated in the decline of many species. However, these are aided by human activity in many cases: for example, insecticides weaken the immune systems of honeybees, enabling pathogens to spread more easily. Climate change is not listed as a major cause of insect declines, and may actually benefit some insects in temperate regions. The impact in the tropics will likely be greater, as species there are more susceptible to increased heat.

The intensification of agriculture is stated to be the primary driver of insect extinctions and declines in the past 100 years. Slowing or reversing these losses will be essential to prevent widespread ecological and humanitarian disaster. Given that a massive portion of our cropland is currently used to grow animal feed, shifting to a plant-based diet will enable us to reduce the amount of land that is currently used for agriculture. This will allow us to restore much of the habitat that was destroyed and possibly reverse some species’ decline and reintroduce extirpated insects.

The authors also argue that we need to change the way we grow our food. We need a greater diversity of crops, and our pesticide use must be reduced. The types of pesticides we use must be more carefully examined, and alternative methods like introducing predatory insects should be considered. Wildflowers and grasses should be planted between fields to increase habitats for pollinators. Crops should be rotated with other plants, such as clover, for the health of the soil and to provide additional insect habitats. Marshlands and wetlands must be restored as well, and pollution of surface water must be kept in check. For animal advocates, this meta-analysis gives us a strong argument for the end of animal agriculture, among other agricultural reforms.

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Owen Rogers is from northern Illinois, raised in the suburbs of Chicago. He became interested in animal ethics at a very young age, when he had several companion animals ranging from a dog to a corn snake. In college, he majored in philosophy with a focus on ethics, and became a vegetarian. In addition to working with Faunalytics, he has also volunteered at animal shelters and participated in environmental cleanups.

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