Sudden, rapid, and enormous declines of insects world-wide, an ‘insect apocalypse’, has received a wave of media attention since 2004. Since then, scientific studies have sought to quantify the phenomenon and to understand what it causing it. Declines of commercial honeybee populations have received the most attention since the global food supply depends significantly on them. But butterflies, beetles, dragonflies, grasshoppers, and other insects have declined precipitously as well. Quantifying the decline across so many species is challenging, but several studies have attempted to do so. One study in Germany found that the flying insect biomass dropped by 76% in 27 years. Subsequent reports have attempted to quantify particulars of declines in abundance and diversity, but the decline of insect populations is a complex and heterogeneous story.

Scientists may argue about the particulars, but there is general acknowledgement that insect biomass is declining globally. Perhaps the most compelling aspect of the story is the rapidity of the decline – massive declines in just decades. There are many reasons that may account for insect declines, e.g. climate change, increasing agricultural acreage, shift to monoculture and industrial agriculture, and increased insecticide use generally. It is difficult to assign causes to such a widespread phenomenon, but there is one correlation that is of high interest. The use of neonicotinoid insecticides has increased dramatically in the past few decades, i.e., approximately the same timeframe as the dramatic insect reductions. The annual use of neonicotinoids in the US increased from near-zero in 1994 to almost 8 million pounds in 2014, and they are used widely for maize, canola, soybean, oilseed rape, cereal, rice, cotton and sunflower crops. Neonicotinoids have been widely adopted as safer replacements for previously used insecticides because they are selectively toxic to insects while relatively nontoxic to vertebrates, and because of growing insect resistance to carbamates and organophosphates (which were killing farmworkers).

There is insufficient evidence to say unequivocally that neonicotinoid compounds are responsible for a widespread decline in insect numbers. Still, some countries are very concerned about the global insect declines, and about the correlation with neonicotinoid use. The 28 countries of the European Union have passed legislation to ban the use of three neonicotinoids for all outdoor settings, although neonicotinoids are permitted for use in permanent greenhouses. In the U.S., the Environmental Protection Agency has been reviewing assessments of neonicotinoids for risks to ecological systems, human health, pollinators, and non-target insects, and plants, and microbes. A final interim decision in expected in 2024.

As the U.S. and Europe have diverged in their approaches to neonicotinoids, insect populations will reflect this policy difference if neonicotinoids are a significant factor in the rapid declines of the past several decades. Until a ‘smoking gun’ is found, or possibly a range of factors that have contributed to the insect apocalypse, we in the U.S. can make personal decisions that can make a difference in our local environments.

First, what the heck is a neonicotinoid? Neonics are insecticides, which are pesticides specifically targeting insects. ‘Pesticide’ and ‘insecticide’ are not synonyms, rather, insecticides are a class of pesticide. Other common classes of pesticides are herbicides, fungicides, and rodenticides. Yes, they are related to nicotine, an organic* chemical occurring naturally in tobacco plants. But neonics are a group of organic compounds that do not occur naturally. So why go to the trouble to make something in the laboratory that resembles nicotine, but isn’t?

Nicotine is a well known systemic insecticide that is toxic to sucking insects. The trouble is that it is also toxic to mammals. A favorite home-made insecticide of our great-grandparents’ time was cigars soaked in water, then run through a blender, sieved and sprayed. Extremely effective, toxic, and dangerous! And a perfect example of how not everything home-made is safe. By identifying the specific way that nicotine targets the receptor chemicals in an organism’s cells, a nicotine-like chemical can be designed that will retain toxicity toward insects but minimize its effect in mammals. An entire class of neonicotinoids has been developed with highly specific toxicity to insects, but with lower risk for other species, specifically humans, other mammals, and birds. Still, there is growing evidence that neonicotinoids can adversely affect the health of invertebrates, birds, fish, and mammals, including humans, even if its effects are not lethal.

The most common neonicotinoids used currently are: imidacloprid, clothianidin, thiamethoxam, dinotefuran, acetamiprid. Other compounds continue to be developed for sale, so this is only a current listing. These compounds are widely used because of their effectiveness in killing target insects, but also because of their stability and wide range of possible application methods. They can be used in irrigation mixtures, sprays, coatings, soil drenching, and stem and trunk injections. They are widely used for agricultural production of field crops, and for growing ornamental plants, grapes, and tree fruit. They are also used to treat forest trees, and trees and grass in a variety of urban settings (parks, golf courses, public right of way, etc.), as well as for residential use and as a topical flea treatment on cats and dogs.

Unfortunately, when you’re shopping for an insecticide, the labels are not going to specify if something’s a neonicotinoid. All neonics are systemic, but not all systemic insecticides are neonics. There are web resources that allow you to quickly research pesticides by brand name or by active ingredient, so you might want to bring reading glasses and your smart phone when shopping.

Because neonicotinoids are systemic toxins, they are taken up throughout the entire plant. A major use of neonicotinoids in commercial agriculture (both for food and nursery stocks) is treated seeds, eliminating or minimizing the need for insecticide treatments of growing plants. Primary exposure to insects occurs by ingesting any part of the treated plant – tissue, pollen, nectar, flowers, fruits, and roots, and by ingesting untreated plants contaminated by residues from treated plants. Human exposure occurs through ingesting or handling treated plants, ingesting water contaminated by neonicotinoids, inhaling dust generated during planting treated seeds, and inhaling pollen released by treated plants. Studies of neonicotinoid bioaccumulation are of interest, but have not yet been conclusive.

The stability of neonicotinoids means that these compounds take months to years to break down in soil, depending on the specific compound and soil conditions. Persistence in water is on a timescale of weeks to months. A recent report documented the ‘ubiquitous’ presence of imidacloprid in Florida surface water finding its presence in 24 of 25 watersheds. Concentrations varied depending on location and season, but could be high enough to produce ‘deleterious, and in some cases fatal, effects on aquatic invertebrates’. In California, 89% of the samples taken from rivers, creeks, and agricultural ditches contained imidacloprid. In the Midwest, a small study detected multiple neonicotinoids in all nine streams that they sampled. This mobility and nationwide ubiquity is important because even plants that have not been treated with neonicotinoids are able to absorb them from contaminated soil and water. It seems likely that neonicotinoids could become widespread throughout the plant world and the entire food chain in the U.S.

Even if neonicotinoids are not lethal to non-target species, they have been shown in recent studies to impair flight behavior and migratory ability in locusts and songbirds. Direct and indirect effects of neonicotinoids on non-target vertebrates have also been reported from rats, mice, rabbits, birds, frogs, fish, reptiles and deer. Some recent studies reported that human prenatal and adult exposures to neonicotinoids are linked with Autism Spectrum Disorder, heart defects and neurological symptoms.

With all this bad news, what can we can all do to positively impact our local, if not global, environment? Here are a few thoughts:

• seek alternative solutions to pesticides. Integrated Pest Management involves using cultural and mechanical techniques in addition to chemical, to manage pests. The simplest methods might include planting pest-resistant selections (cultural), and pulling or smothering weeds rather than using an herbicide (mechanical). An alternative to neonic use in gardens would be to squash aphids with your fingers! Extremely effective mechanical control. But the best-adapted plants will not have defenses against introduced insect pests or diseases. And, some pests just cannot be controlled without at least some use of chemicals, and are detrimental to ecosystems and/or human health without some level of control. Balancing all this is the Art of Integrated Pest Management. Unfortunately it is not as simple as ‘Just Don’t Spray’, or using chemicals that claim to be ‘Organic’ or ‘Safe’. Organic fungicides made from copper and sulfur are very toxic to bees, and neem and horticultural oils, marketed as safe for beneficial insects, are not. Insecticidal soaps are another example. Like neem oil and horticultural oil, they work by smothering and dessicating soft-bodied insects, but that includes all larval forms of predatory insects.

• use contact insecticides at night and/or when insects are not flying. Contact insecticides have to be sprayed directly on the target to work and will have little effect on insects that wander by once the spray has dried.

• be very selective of what plants you apply neonics or any other systemic insecticide to, taking care not to exceed recommended dosage. Pesticide labels aren’t there for amusement value, they represent millions of dollars in research, and your use of the pesticide constitutes a legally binding agreement to follow the label requirements. Yes, you can be investigated and prosecuted for misuse.
• support organic production of agricultural products, seeds, and nursery plants
• vote for politicians (and write letters to let them know how you feel) who support agricultural reform

• share your thoughts with interested parties. But, keep in mind that shaming and judging don’t work – people shut down when they feel shamed or judged. ‘Just Don’t Spray’ is also too simplistic to be useful. Yes, there are situations where it may not be necessary to use a chemical spray, and some uses ought to be discouraged, but it’s a complicated subject without a one-size-fits-all solution. What works in your little city garden, won’t work at a larger scale on a farm or forest.

Alternative insect controls in gardens:

First of all, bugs eating your plants are what’s feeding the birds and other wildlife in your garden. Try to share

• Aphids can be easily controlled in small gardens by either squashing them with your fingers, or hosing them off your plants. Birds will gladly eat your aphids if you let them, and would appreciate their not being contaminated with any kinds of insecticides, neonic or not.
• Mites are creatures of hot dry dusty weather, so a regular hosing of the undersides of the foliage will keep mites down. Avoid planting mite-susceptible plants next to hot surfaces like concrete or brick. A thick organic mulch can help too. Neem oil in particular seems to cause explosions of mite populations – it’s killing off mite predators, which are susceptible to most ‘safe’ insecticides.
• Scale, mealybugs, lace bugs and thrips are difficult to control and big reasons neonics are so popular. Best to ignore them if you can, or prune them off if necessary, or even remove infested plants. Natural predators can exert reasonable control if allowed to do so. This means avoiding the ‘safe’ insecticides like soaps, oils and neem, which one might think are the safer alternatives to neonics; but they kill larval predatory insects.

Other pesticides such as herbicides and fungicides are often accused of harming insect populations, probably mostly through confusion of ‘pesticide’ with insecticide’, although some do have deleterious effects. Organic fungicides in particular tend to be poisonous to bees and other insects – anything based on copper or sulfur. This is a direct effect. Herbicides tend to have an indirect effect, if any. You’ve probably heard Roundup accused of being bad for Monarchs. But it’s an herbicide, and the active ingredient does not have insecticidal activity. The problem is two-fold. The primary problem is that broadcast spraying of Roundup on genetically-modified Roundup-Ready (herbicide resistant) crops like corn and soy eliminates larval and nectar plants in and around agricultural fields, eliminating Monarch habitat over huge areas of the Midwest. Secondarily, the proprietary surfactant that makes plain glyphosate into brand-name Roundup is known to be deleterious to invertebrates. Plain glyphosate by itself is considered safe. Limited applications of plain glyphosate that don’t wipe out host plants are not a real concern and in fact are invaluable in habitat restoration. You can buy plain glyphosate for home garden use, and careful spot-spraying of difficult weeds will not affect insect populations. (Unless you’re Regina’s neighbor eliminating his reed canarygrass, normally a laudable activity, but in this case you cut her Woodland Skipper population in half with a single application of glyphosate. Despite her having plenty of unmowed and unsprayed weedy grasses available for them.)

* Organic compounds are chemicals that contain carbon and hydrogen, but can also contain oxygen, nitrogen, and sulfur. Organic pesticides are generally those derived from natural sources, e.g. pyrethrins extracted from chrysanthemum flowers. But not all organic pesticides are safe, either for insects or other organisms. See the discussion of nicotine, above. To use the pyrethrin example, these are highly toxic to bees and moderately to highly toxic to other beneficial insects. Mammals can also be affected. Dogs are less reactive, but cats and fish are very sensitive to these compounds. This is just one example. More information is available at:

Resources

https://xerces.org/sites/default/files/publications/13-053_web-screen.pdf. However, this publication is oriented toward larger scale farming and is focused primarily on bees.

General information on pests and pesticides: University of California‘s Integrated Pest Management Program: https://ipm.ucanr.edu/index.html

Their Pesticide Information page is here: https://ipm.ucanr.edu/GENERAL/pesticides.html

WSU Extension Home Gardener Fact Sheets on pests and Integrated Pest Management: https://hortsense.cahnrs.wsu.edu/

National Pesticide Information Center: http://npic.orst.edu/ Search for product names by active ingredient, or active ingredients by product name: http://npic.orst.edu/NPRO/# (AI means Active Ingredient, not Artificial Intelligence

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