We hear that pollinators are in dire straits as harmful and invasive insects seem to proliferate. But how are all other bugs do?
In recent years, scientists have started to sound the alarm bells about a suspected “insect apocalypse”. Research initially outside Europe suggests that arthropods – a category of invertebrates that include insects – are experiencing sharp declines globally in terms of diversity and abundance.
Half of the million animal species that scientists say will be threatened with extinction in the next few decades are insects, according to an article from 2020 in the review Biological conservation. Granted, there are a lot of insects to begin with – around 5.5 million species worldwide. The number is so high that only about a fifth of the species have been named.
Some researchers suggest declines may only be cyclical or regional, but most say there is no time to waste in reversing troubling trends. And, while data on the local population isn’t easy to come by, they say many of the trends happening globally are likely happening in the Chesapeake Bay area. These declines could also present obstacles, or at least complications, in the effort to restore the bay.
“We know different places have different environmental stressors, different climates, different local managements,” said Daniel Gruner, associate professor of entomology at the University of Maryland. “But we can, from these global studies, identify some major threats that are probably quite universal.”
Many of the factors that work against overall environmental health – habitat loss, urbanization and the widespread use of pesticides – have a disproportionate impact on insects. In many ways, the health of insects is an approximation of that of the entire ecosystem.
Insects recycle nutrients, maintain pest balance, and disperse seeds. Pollinators and soil-improving insects also make an irreplaceable contribution to agricultural production.
“Insects are very good indicators of the quality of the environment,” said Alejandro Del-Pozo, assistant professor in the department of entomology at Virginia Tech University. “If we’re going to look at the streams and streams and understand if something specific is going on… look at the bugs.”
But tracking insect populations can be tricky, and trends vary widely by region and species. It can also be difficult to find historical demographic data collected using methods similar enough to allow comparisons over time.
Yet the 2020 article indicates that between 5% and 10% of insect species have been lost over the past two centuries and that the rate of loss is accelerating. To 2021 paper published by the National Academy of Science estimated that annual declines in insect abundance hover around 1 to 2%.
Why the decline?
Several environmental factors could put insects at risk. Fragmentation and habitat destruction can greatly reduce some populations and lead to co-extinctions – the disappearance of not only a single species but also one or more that depended on it. Climate change and an influx of invasive species are also believed to play a major role.
And pollution, especially the use of broad-spectrum pesticides, is seen as a major culprit. A study published this spring in Science magazine found that the chemical makeup of modern pesticides, although applied in decreasing amounts since the 1960s, has dramatically increased in toxicity, especially to insects and aquatic invertebrates. These pesticides also harm soil invertebrates such as earthworms, beetles and ground-nesting bees, according to another study.
Bonnie Raindrop, program director at the Maryland Pesticide Education Network for the Pesticides and the Chesapeake Bay Project, said she talks a lot about the impact of these chemicals on bees and other pollinators.
“But it’s important to connect the dots so that people understand [that] what happens to bees happens to all other insects, ”she said. “Losing the insect world would have devastating effects on all of us.”
The losers and the winners
In the Bay Area, some insects do worse than others. The number of native ladybugs, for example – including the New York State insect, the nine-spotted ladybug – has declined dramatically over the past 30 years.
Meanwhile, the populations of non-native species like the multi-colored Asian ladybug flourished. These so-called Halloween ladybugs were brought to North America to consume plant pests. Now, they compete with native ladybugs for food and are known to invade homes in droves in October to overwinter.
Big silk butterflies, like the bright green moon butterfly, are also much harder to find, according to a study. Scientists believe this is likely due to another non-native species: a deadly parasitic fly introduced over a century ago to control gypsy moth caterpillars, but which now “controls” hundreds of other moth species. .
“I’ve only seen a few of them over the years,” Gruner said of the large moths in the Saturniidae family, such as the red-brown and imperial yellow-brown cecropia. “In the past, we have introduced [species to combat unwanted pests] without much testing to see if they would also consume native insects.
Many arthropods play a specific role in a specific ecosystem. This makes them less resilient to change.
The insect of the state of Maryland, the Baltimore Checkerboard butterfly, is one of these specialist insects. Its caterpillars feed almost exclusively on the head of the white turtle, a wetland plant with large white flowers. But the turtle head has become rarer as invasive plants, development and sea level rise have transformed many wetland habitats. Maryland now considers the checkerboard to be a species at risk.
Tyler Rippel, a doctoral student at Georgetown University, was studying how a loss of specific habitats in coastal environments can interrupt the delicate dance of insects in these ecosystems. Many are affected when a single type of seagrass, for example, invades a once diverse wetland.
“People don’t really follow that in coastal ecosystems unless they’re studying fish or oysters or molluscs or some kind of important agricultural species,” Rippel said. “Not many people care about these insects, so we wanted to highlight how they influence the environment.”
Gruner said there are winners and losers in the vibrant world of insect populations, with species like the Asian tiger mosquitoes thriving in a modern Chesapeake watershed as some native species struggle.
In these scenarios, Gruner said, “Even if the total abundance and biomass of the insects are found to be stable over time, the underlying biodiversity is almost certainly in decline.”