The Xerces Society is pleased to announce our new Searchable Systemic Insecticides List, which allows anyone to understand the dozens of insecticides currently registered in the U.S. that are designed to permeate plants from within. Systemic insecticides can render some or all of a plant toxic to insects that feed on plant tissue and are commonly used to suppress herbivorous sucking or chewing insects like aphids, caterpillars, and root nematodes. Unfortunately, systemic insecticides also harm beneficial insects.
Beneficial insects consume systemic insecticides, too
Just as humans have arteries and veins that circulate nutrients and waste products around the body in the bloodstream, plants also move water and nutrients through a system of vessels. Systemic pesticides (whether insecticides, fungicides, herbicides or other pesticides) are absorbed into plants and then transported through plants via these vessels.
Once absorbed into the plant, a systemic insecticide may reach stems, leaves, pollen and nectar. This means that the chemicals can be consumed not just by insects that may cause damage to plants, but also by bees, larval and adult butterflies, and the many beneficial predators and parasitoids that eat pollen or nectar as adults. Systemic insecticides have also been detected in guttation droplets, (tiny droplets exuded from plants on hot, humid nights, utilized for water and nutrition by some insects), in autumn-shed leaves from treated deciduous trees, and in honeydew, a sticky substance excreted by aphids and some other species and an important food for many insects.
Forty systemic insecticides in use in U.S.
Systemic insecticides include those in the neonicotinoids family, which have been widely recognized for their risk to bees in part because they are far more toxic to bees than most other insecticides and are very persistent, frequently detected inside plants years after application. However, dozens of other systemic insecticides are in use in the U.S., including many newly approved chemicals that are not as commonly known. They are used in a wide array of agricultural crops and applied to landscape plantings, turf, trees, nursery and greenhouse plants, and non-crop areas.
An overview of these chemicals and their impacts is now available on our new webpage: Systemic Insecticides: A Reference and Overview. From there, you can link directly to the Searchable Systemic Insecticides List to look up information about specific systemic insecticides. There you will find more details about these insecticides, including use sites, degree of toxicity to bees, persistence, and predicted strength of systemic activity. You can also download the full table, sorting through the information presented for all the insecticides.
Because systemic insecticides are usually quite water-soluble, they have become common water pollutants across the country, putting aquatic insects, including mayflies, at risk. Photo: Flickr /Ian Boyd, CC BY-NC 2.0
EPA approval doesn’t mean pesticides are safe
As neonics have made the headlines, many have turned to other, supposedly safer systemic insecticides. Many people mistakenly believe that if approved by the U.S. Environmental Protection Agency, a pesticide is de facto safe. But this isn’t exactly true. Not only does EPA accept some risk for pesticides, sometimes they don’t know the impact of the pesticide uses that they approve.
For example, the new systemic insecticide cyantraniliprole is permitted for use in nurseries and on greenhouse plants – including on ornamental landscape plants that may be planted in pollinator gardens later – at rates three times higher than the highest rate studied in the field prior to EPA’s approval. Pollen studies on food crops showed that the highest residues occurred in fruit trees treated before bloom, resulting in cyantraniliprole in pollen at levels concerning to bees. Even with this data in hand, the EPA approved applications to nursery plants, including trees, at far higher rates than those that were studied on the fruit trees. A general rule in toxicology is “the dose makes the poison” and this means that higher rates usually result in higher residues. In this case, EPA didn’t require data on how those higher residues affect bees before approving the chemical. Given that this insecticide is highly toxic and highly persistent, this permissive approach is very concerning.
Caterpillars of dwindling butterfly species, such as this monarch caterpillar, are vulnerable to injury or death if they consume plant tissue contaminated with insecticides. Systemics are often found in greater concentrations in leaf tissue than in pollen or nectar. Some newer systemic insecticides, such as chlorantraniliprole, are promoted as bee-safe but are actually very toxic to monarch caterpillars. Photo: Xerces Society /Stephanie McKnight.
Systemic insecticides may still drift
One touted advantage of systemics and perhaps a reason leading to widespread adoption, is that they can result in less drift, since they are often applied directly to the soil as granules or drenches, or are injected or painted on some plants. But the “no-drift” advantage has been shown to be more illusory than real under certain circumstances: abrasion of seeds coated in systemic insecticide generates dust that is highly contaminated and moves off-field during planting (Krupke et al. 2012).
Another concern with soil applications is that some systemic insecticides exhibit very slow soil degradation rates (Bonmatin et al. 2015) and thus may be available for plant uptake over an extended period of time.
We know it’s hard to pronounce individual chemical insecticides and harder still to keep track of them all, but knowledge is power. Please learn more about these insecticides by perusing our new resource, and to protect the little things that run the world, avoid the use of insecticides in every way you can.
Bonmatin, J-M, C. Giorio, V. Girolami, D. Goulson, D. P. Kreutzweiser, C. Krupke, M. Liess, et al. 2015. “Environmental Fate and Exposure; Neonicotinoids and Fipronil.” Environmental Science and Pollution Research International 22 (1): 35–67. https://doi.org/10.1007/s11356-014-3332-7.
Krupke, Christian H., Greg J. Hunt, Brian D. Eitzer, Gladys Andino, and Krispn Given. 2012. “Multiple Routes of Pesticide Exposure for Honey Bees Living near Agricultural Fields.” PloS One 7 (1): e29268. https://doi.org/10.1371/journal.pone.0029268.
For Further Reading:
Visit the new Systemic Insecticides: A Reference Guide and Overview website.
Read the Xerces Society Recommendations to Protect Pollinators from Neonicotinoids.
Read about some of the general concerns posed by the use of systemic insecticides in this 2013 open-access paper by Sanchez-Bayo, Tennekes and Goka.
Learn simple steps for Buying Bee-Safe Plants.
Browse science summaries featuring systemics insecticides and other pesticides at Xerces’ Impacts of Pesticides to Invertebrates database.