An unusually large influx of tiny insects called aphids have been sucking on Dallas-area pecan trees in recent weeks. After they’ve had their fill, they “excrete” the waste out their back ends and onto cars, driveways and sidewalks. “Texas is covered in a sticky, icky goo,” declared a Dallas Morning News headline. Other news outlets offered tips on how to clean up the mess.
It’s not just Texans who should be grossed out. Scientists who study the relationship between insects and plants have long predicted that a warming climate would benefit aphids and other plant-eating pests. The Texas drought, which occurs as the state experiences rising temperatures under the influence of climate change, is just one example. Elsewhere, surging populations of plant-eating insects are disrupting farms and the food supply chain, causing problems far more serious than sticky windshields.
Discussions around climate change and its impact on animals is often limited to large, charismatic species like polar bears and sea turtles. Butterflies and pollinators might earn mentions, but generally insects get far less attention than species that translate easily into stuffed animals. That’s an understandable but grave oversight that needs to change if we want to have a chance at mitigating hundreds of billions of dollars in potential losses.
Insects, unlike sea turtles, provide services critical to the functioning of the environment and human societies. According to a 2015 study, 5% to 8% of global crop production — worth as much as $577 billion — is dependent on pollination. A less obvious but no less important service is the processing of dung into fertilizer, a function that’s performed by many organisms. A recent study suggests that the dung-eating services provided by just one, the simple dung beetle, saves the US cattle industry around $380 million in dung recycling services annually. Other ecosystem services provided by insects, including pest control, are far more difficult to price. Forensic entomology, the science of using insects to investigate crime-scene deaths, is highly dependent upon decades of data on corpse decomposition rates pegged to specific temperatures. And what price would Texans pay for a swarm of aphid-eating ladybugs to stop the goo?
Alas, these crucial organisms are facing what some prominent scientists have recently started calling the “insect apocalypse.” Last year, a group of scientists estimated that insect abundance is declining by 1% to 2% a year due to a range of stressors, including insecticides, herbicides and climate change. This year, a different study assessed samples of nearly 20,000 different insects and found a 63% decline in insects in climate-stressed agricultural areas where most natural habitat has been removed (removal of trees intensifies heating effects, among other problems). Another recent study found that the rising frequency of unusually hot days in North America and Europe is contributing to higher local bumblebee extinction rates. And in forensic entomology, a growing body of research suggests that disappearing and migrating insect species — such as the blowfly — are undermining the usefulness of the investigative method, potentially hindering law enforcement.
Not every insect species will suffer losses due to a changing climate, and many that won’t are precisely the kinds of bugs that humans would rather do without. Many pests, especially the varieties that feast on crops, are beneficiaries of climate change. In 2013, scientists observed that the home ranges of many pests have been shifting toward historically cooler regions since at least 1960. That shift continues. Scientists estimated this year that a warmer climate was contributing to a 70% expansion in the US habitat for the brown marmorated stink bug, a common and destructive agricultural pest.
Greater amounts of precipitation generated by warming oceans is also affecting harmful bug populations. For example, over the last 15 years the western Indian Ocean has experienced historically powerful cyclones. In 2019 and 2020, the rain from those events created ideal conditions for locusts to breed, hatch, develop and, ultimately, damage hundreds of thousands of acres of sorghum, corn and wheat in Ethiopia, alone.
There are also more subtle means by which climate change can promote pests and the destruction of economically significant plants. One study found that increases in temperature were accompanied by an increase in the numbers of Maize Stem Borers, a pest common in parts of Africa, and a decrease in the parasites that feed on them. That disconnect, in turn, led to greater devastation of corn crops. Drought, such as what Texas has faced, can weaken a plant’s natural defenses, thereby attracting pests, while higher CO2 levels can decrease the nutritional value of plants. “If insects face a plant that won’t give them all the nutrients they need, they’ll consume more,” explained Esther Ndumi Ngumbi, an assistant professor of entomology at the University of Illinois. “That’s another unfortunate side-effect of drought,” said Ngumbi, who studies the relationship between plants and insects and spoke to me by phone.
Her research is also focused on the impacts of pests on farmers, and she’s been troubled by what she’s observed, especially among small farmers in emerging markets. “A Kenyan farmer works one acre of land. If insects come, if drought comes, that takes away their crop, which means they can’t provide for their family.” In more developed regions, the farms are larger, but the impacts are still significant, especially as consumers face higher inflation.
Research efforts to develop and disseminate — for free — drought-resistant crops is a critical step to addressing the growth of pests on farmlands. But that’s a longer-term process. For now, Ngumbi would like to see a global effort to better monitor for pests and notify farmers before they migrate onto their lands. In addition, she and others argue that crop diversification, rather than single-crop monocultures, can help to slow pests.
None of these steps can reverse climate change’s impacts on insects. But they can prepare humans for the consequences that are already happening and inspire long-term thinking about adaptation. If we’re not talking about it then we’re not going to be doing anything about it, and doing nothing will only benefit the pests. That should bug everyone.
Bloomberg
