What are neonicotinoids? An Auckland doctor explains why threats to bugs should be taken seriously

Illustration: Anna Crichton

Insect numbers have declined shockingly in recent years. But perhaps the biggest problem is that most of the world doesn’t realize how alarming this is.

Words: Dr Roderick Mulgan

Sex is tricky for plants. Although they have male and female appendages, they can’t move. Early in evolution, plants such as conifers did their best by releasing clouds of pollen from male cones and hoping some wound up on a female cone nearby. Martyrs to hay fever continue to pay the price.

More efficiently, flowers were invented; colourful nectar dispensers entice an insect to crawl in for a drink and get stuck with some pollen, which winds up in the flower next door soon after. The system has been a runaway success, particularly for plants that produce food. Nuts, fruits and vegetables all make widespread use of it, which means they — and us — rely utterly on insects continuing to provide the service. Unfortunately, there is a real question mark over whether they will.

The word crisis is overused in environmental discussions — few ecological issues are described as anything less — but there is a quiet and shocking calamity unfolding with insect life that deserves no other label. Multiple surveys in multiple countries have shown dramatic collapses in insect numbers in the past 20 years. These disasters don’t photograph as well as bulldozed rainforests or polar bears on melting ice floes, but they are every bit as sinister for business as usual on planet Earth. Sadly, they generate few headlines.

Modern agriculture bends much of the natural world to its will. Plants are engineered, chemicals are sprayed on, and water is piped in, but we really, really (and I mean really) have nothing to replace pollinators. In field trials in regions of rural China, where labour is plentiful and human rights are not (and insects no longer exist in adequate numbers to keep orchards going), lightly reimbursed people are sent out to move pollen between apple tree flowers with chicken feathers and fine paintbrushes. The technique is unlikely to catch on. The wind, like the conifers mentioned above, pollinates some high-volume crops such as wheat and corn but almond milk, that lunchtime apple, coffee, orange juice, roast pumpkin and most other interesting and healthy botanical edibles come into the world courtesy of pollinating insects.

Which are not just bees. Bees are the poster bugs of pollination because they are most amenable to being carted around in wooden boxes to do the job where farmers want it, but they are only the most visible. There are dozens of types of wild bees that labour alongside their commercially cultivated cousins, but multiple species of butterflies, moths and hoverflies are also dedicated pollinators, as are beetles and wasps. Some pollinators have evolved a focused co-dependency on a single plant. Chocolate, for instance — or more properly, cacao — starts with flowers that are so tiny only a particular midge species can do the business. If anything happened to that midge, it would end unctuous foil-wrapped treats worldwide.

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Insects also decompose stuff. When plants and animals die or lose bits of themselves, such as leaves, that biomass needs to be returned to the food chain, which means something has to eat it. Flies, beetles and ants regularly oblige. If they didn’t, it is not just a case of the world being awash in dead things that don’t break down. It is a case of no humans existing to observe it. We are all composed of atoms that have done duty in multiple other bodies before our one, and there would be nothing to make us out of if building blocks didn’t cycle.

The third great contribution insects make is being edible, often although not exclusively by other insects. Losing some insects means losing others that need them. It also means a serious dent in birdlife and populations of freshwater fish. There is no viable ecosphere without insects, yet recent data shows they will not continue holding up the whole edifice if things continue.

Readers of a certain age will recall that long car trips used to mean squashed bugs on the windscreen at the end. This doesn’t happen anymore, and similar observations abound. Monarch butterflies in the United States once migrated to México for winter in such numbers they appeared on weather radar and buckled the branches of roosting trees when they arrived (that is a lot of butterflies!)

Today, a fraction of the traditional hordes make the journey and scientists anticipate the phenomenon will soon disappear. Much the same is found everywhere experts look.

A study in Germany monitored sticky traps in 63 different places and found insect biomass had declined 76 per cent during the past 27 years. A similar study found ground insects in Puerto Rico’s Luquillo rainforest have fallen to a tiny proportion of their numbers in the 1970s.

Numbers of insect-eating frogs and birds had fallen in parallel. Dozens of other studies have produced equivalent findings. A recent summary of 73 of them concluded that the sword of extinction hovers over 40% of all the world’s insect species.

Some of the forces in play have been creeping up on us (and them) for decades, particularly the assault on plant diversity. Monoculture crop fields are oceans for pollinators, who exist to fly between the different variegated flowers nature throws up. Worldwide, agriculture continues to swallow wild spaces, and even hedgerows and mixed crops, which can be lifelines for insects, are considered unhelpful for maximum profits.

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Suburbia is often a better bet than farmland because we like to surround ourselves with plants, but there are still serious insect limitations, particularly with grass. Grass is designed to be wild and weedy, but humans think grass is carpet, not savannah, and expend much trouble to cut down its natural urges. Humans even want grass to be carpet when there is no imperative to walk on it, like roadside berms. Berms are an ideal opportunity to compromise with nature; they tend to be manicured to an inch of their lives, usually by a council contractor with a ride-on, for little more than appearance.

If we saved rates and fossil fuel and left them alone, they would quickly become a tangle of seed heads and weed flowers to the delight of flying wildlife, but the cultural shift in how we like our streets to look would be massive.

Modern light pollution undermines night flyers such as moths, who are programmed to navigate by the moon and die circling street lights. Juvenile insects don’t develop properly if the day-night cycle is hijacked by artificial light, and insects that make bioluminescence to find mates can’t compete.

Insect numbers have also been observed in steep decline far from human habitation, as with the Luquillo rainforest, which has prompted experts to wonder if the world getting hotter is a factor. It is difficult to draw direct cause and effect conclusions, but when temperatures exceed historic levels, it is plausible that tiny lifeforms with delicate and complicated lifecycles will be vulnerable.

All of which is dire, but one final factor is more alarming than most. Diverse swamps and woodlands have been giving way to efficient agriculture for a very long time, and roads with streetlights keep getting laid, but something new and much more serious has happened just recently. Insect loss has been dramatically worse in the past 20 years, and the difference is widely believed to be due to new pesticides called neonicotinoids.

There is nothing new about pesticides per se or their collateral damage. Growing food at scale uses measures that kill off insect pests, and desirable insects get poisoned along with the others. It has always been this way, but neonicotinoids, related to nicotine, are a relatively recent development. Nicotine has a long history as an insect poison — Victorian gardeners mashed tobacco with water to make insect spray — but neonicotinoids are a modern tweak introduced in the mid-1990s and are now the most widely used pesticides in the world.

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They are popular because they are not particularly toxic to vertebrates, which is all very well, but they are indiscriminately toxic to insects. They work by percolating through the tissues of a growing plant, so an insect that eats the plant will be poisoned, but they also wind up in pollen and nectar. Neonicotinoid persist a long time, which farmers like because they don’t have to be applied often, but that also means they accumulate in soil and water.

Studies have found them on fruit and vegetables, in sparrows’ feathers (from eating insects), in wild honey, in human hair. It is difficult to prove their role in insect collapse, but the circumstantial case is disturbingly strong. Something known to kill insects indiscriminately, which lasts a long time in the natural world and passes up the food chain, has been sprayed around the planet in the same time frame that the insect collapse became exponential. If I were on the jury, I’d convict.


A fast-growing British campaign aims to encourage people to let their lawns go wild. Rather than knocking the grass into shape, the goal for No Mow May is for grasses and weeds to go to flower to feed insects.

May, of course, being the ideal month in the northern hemisphere for plants to flower. An adult bumblebee needs the nectar of eight flowering dandelions to meet its baseline requirements for survival.

Citizens are encouraged to regard unruly lawns as a badge of good environmental citizenship, and if that’s a bridge too far, they are asked to at least let their berms go to seed.


1. Hallmann CA, Sorg M, Jongejans E, Siepel H, Hofland N, Schwan H, et al. (2017) More than 75 per cent decline over 27 years in total flying insect biomass in protected areas. PLOS ONE 12(10): e0185809.
2. Lister BC, Garcia A. Climate-driven declines in arthropod abundance restructure a rainforest food web. Proc Natl Acad Sci U S A. 2018 Oct 30;115(44):E10397-E10406.
3. Sánchez-Bayo, F., & Wyckhuys, K. A. G. (2019). Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation, 232, 8–27.


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