In April 2018, the European Union voted to ban all outdoor uses of neonicotinoid insecticides, also known as neonics. First introduced in the 1990s, this new class of insecticides has rapidly gained popularity to become the most widely used pesticide in the world. Neonics, which are chemically similar to nicotine, affect the central nervous system of insects. Farmers and gardeners apply them as seed coatings, foliar spray or granules, and the insecticides are absorbed into the plants as they grow.
What’s the good news? As systemic pesticides, these chemicals are incorporated into plant tissues to protect them against many insect pests. And because neonics were designed to bind specifically to insect nerve cells, they have low toxicity for humans and other mammals.
What’s the bad news? Once applied to crops, lawns, or gardens, neonics hang around for a long time and accumulate in soil, rivers and ponds, and groundwater. And studies conducted in the last two decades have revealed some alarming, though unintended, consequences for beneficial insects and other invertebrates.
Let’s start with bees, since everyone knows they provide vital pollination services for crop production. Dozens of studies have established that at typical dosages, neonics are highly toxic to both native bees and honeybees. In addition to outright mortality, they cause many adverse symptoms like paralysis, impaired mobility and orientation.
Fewer studies exist for other insects, and I know of no work done to see how neonics affect fireflies. But when the most commonly used neonic, imidacloprid, was applied as a lawn treatment, it lowered the abundance of non-target insects overall by 50 percent. In other studies using ground beetles and ladybird beetles (predatory insects commonly used in integrated pest management and as bioindicators), imidacloprid-treated soil or seedlings caused high mortality and neurotoxicity (paralysis, trembling, loss of coordination) for both adults and larvae. In yet another test, adults of 18 different ground beetle species were exposed to corn seedlings treated with realistic doses of 3 different neonics; in all cases, nearly 100% of these beetles died within 4 days.
While multiple factors are undoubtably at play, insect populations have recently shown startling declines worldwide. Since 1990, butterfly populations in Europe have been cut in half. A 2017 study done in German nature reserves discovered that flying insects have declined by more than 75% over the past 30 years. Vanishing insects are a big problem, because insects forge an essential link in nearly all terrestrial food chains. Without insects, our world would be unrecognizable.
So what about fireflies? Remember – in spite of their various common names (including lightningbugs), these luminous being are neither bugs nor flies. They’re beetles. And they may seem like creatures of the skies, but fireflies actually spend most of their lives down in the dirt. Firefly larvae spend up to two years underground, eating and growing. Once they transform into adults, they will only live a few short weeks.
So during their juvenile stages, fireflies can get exposed to pesticides in the soil or from treated plants. And considering the fact that they’re beetles, the negative impacts of neonics already shown for other beetles might apply to fireflies, too.
Neonics could also harm fireflies through a more circuitous route. Although designed to combat pest insects, neonics have also been shown to be highly toxic to earthworms, which are a major food source for larval fireflies.
What’s the bottom line? We don’t know for certain that neonics can harm fireflies. But reliable scientific evidence has already proven that neonics hurt many non-target, beneficial creatures, including bees, beetles, and earthworms. So I think it’s just common sense that anyone who wants to protect fireflies should avoid using neonics on their crops, their lawns and their gardens.
Learn more about how neonics harm bees: https://xerces.org/neonicotinoids-and-bees/