Insecticide Inflicts Collateral Damage on Soil LifeColony collapse disorder (CCD) is something I have been monitoring since it was first identified by entomologists two decades ago. CCD occurs when the vast majority of bees in any given colony – generally worker bees – die unexpectedly. Because the queen bee needs the nectar provided by these workers to nurse new bees, ultimately the entire colony collapses.

Since its emergence and identification, CCD has remained a major threat to most of agriculture. This is not an exaggeration. According to CNN science reporters, honeybees and wild bees are the most important pollinators of many of the fruits and vegetables we eat. Of 100 crop species that provide 90% of our global food supply, 71 are bee pollinated.

The dollar value of pollination of food crops by bees in the U.S. alone is estimated at $16 billion, and insect pollinators in general contribute $29 billion to U.S. farm income. There are at least seven factors triggering CCD events, the two most major ones being Varroa mites and pesticide poisonings.

With respect to the latter, I recall my involvement as a field crops Extension agent with the pesticide applicator certification pilot program in 1975 in Otsego County – one of two New York counties chosen for that pilot program. I remember learning that the ULV (ultra-low volume) concentrations of the insecticide carbaryl (Sevin) were declared toxic to honeybees by the newly formed Environmental Protection Agency.

Evidently, the honeybees mistook carbaryl crystals for pollen granules, taking them back to the hive to feed their larvae what amounted to their last meal. ULV formulations are sprayed by crop-dusting aircraft to minimize cargo weight. CCD events are very visible, even to untrained observers. Less visible, but equally devastating – ecologically as well as economically – is the biological trauma taking place under our feet, or just at foot level.

To help me investigate such trauma, a former fellow county ag agent forwarded me a scientific paper titled “Neonicotinoid Seed Treatments Have Significant Non-Target Effects on Phyllosphere and Soil Bacterial Communities,” by Mona Parizadeh et al. This paper was published on Jan. 13, 2021 and can be read at the Frontiers in Microbiology website at

I’ll try to hit the high spots of this document, but first a couple definitions are in order. Neonicotinoids (neonics) are defined thusly: “a family of systemic and neuro-active insecticides, chemically similar to nicotine, introduced in the late 1980s. Like nicotine, they interrupt neural transmission in the nervous system by binding to the nicotinic acetylcholine receptors (nAChRs). Because of the fundamental distinctions between the nAChRs of invertebrates and vertebrates, neonicotinoids are selectively more toxic to invertebrates, like insects (particularly honeybees).”

The second term is phyllosphere: “In microbiology, the phyllosphere is the total above-ground surface of a plant when viewed as a habitat for microorganisms. The phyllosphere includes the total aerial (above-ground) surface of a plant, and as such includes the surface of the stem, flowers and fruit, but most particularly the leaf surfaces.” (The rhizosphere, on the other hand, is the underground environment directly contacting the plant’s root system.)

Scientists state that the phyllosphere and soil are colonized by microbial communities (microbiota), which are of great importance in the regulation of host and ecosystem function. These microbial communities, including beneficial bacteria, play a crucial role in plant growth promotion, decomposition and health control as well as in soil fertility, nitrogen fixation and organic matter production.

Quoting these researchers, “Environmental disturbances (such as cultivation methods, drought, climate change and pesticide treatments) can also alter the bacterial community structure and composition. If a disturbance is persistent, it can cause long-term changes in bacterial community structure and affect bacterial succession. During the last decades, the widespread application of chemical pesticides in agro-ecosystems has influenced many non-target species and their succession patterns. Pesticides can change the interaction between plants and some bacteria, such as nitrogen-fixing rhizobacteria, which may lead to the inhibition of nitrogen fixation. They can also (adversely) affect soil fertility and quality by impacting soil bacterial diversity and function and altering their nitrification, denitrification and mineralization of organic matter.”

In this study, the workers joined forces to assess the effects of pesticides on the phyllosphere and soil bacterial community, specifically focusing on a class of the most widely used insecticide pesticides – neonicotinoids.

Neonic compounds are tiny molecules, highly soluble in water. In North America, neonics have mostly been used as seed treatments to control a variety of foliar and soil early-season insect pests in corn, soybean, wheat and other important crops. These treatments are most widely applied preventively, without any information on the actual presence of the targeted pests. As a result – according to Cornell researchers William J. Cox and Jerome H. Cherney – multiple studies have indicated that neonics often have no significant beneficial impact on crop yield. (Their evaluation was in 2011.)

A more recent study (published in 2020 by Quebec scientists G. Labrie et al.) extensively evaluated yield variations in response to neonic seed treatment with regards to the abundance and incidence of pest populations. That study also reported that there is no significant difference in crop yield when pest pressure is low, which was the case in most of the sites being studied.

Given neonics’ systemic nature, plants take them up from the seed coating and translocate them to different tissues and products, including nectar, guttation and pollen. (Note: Guttation is a process in which water seeps out at the tips or edges of a plant’s leaves instead of the stomates. The water comes from xylem – the main water transport tissue in a plant.) Neonics may remain active for 20 to 30 days in soybean and corn, and up to 200 days in winter wheat. Plants only absorb about 20% of the neonic seed coating. The rest of pesticide persists in soil for up to three years, depending on its active ingredient and soil properties.