How Do Pesticides Affect Honey Bees?

How Do Pesticides Affect Honey Bees?

There’s a lot of information out there about impacts of pesticides on honey bees, and on other pollinators that have agricultural importance (like bumble bees), in addition to information on keystone organisms with social-economical relevance like Monarch butterflies. 

Here, we have pulled together the main findings regarding pesticides and their impacts primarily on honey bees.  We want to also point out that some studies we cite were conducted on bumble bees, which may or may not have the exact impacts on honey bees. While not all pollinators are alike, we can derive an overall imprint about how certain chemicals impact social insects through collectively assessing these studies.


First – Define Your Chemical! There Are Many Pesticides & They Don’t All Act Alike

What are Pesticides?

  • Herbicides
  • Fungicides
  • Insecticides
How herbicides have non-intended consequences on pollinators through their mechanisms of action on plants.

Herbicides are chemicals that target plants for death and/or reduced growth. They can either kill the plant, or they can restrict the flowers and seeds it can produce.  

Fungicides are chemicals that target fungi, protozoa for death and/or reduced growth. They can be applied to a wide range of things including plants, animals, bacteria and other fungi.  

Insecticides are chemicals that target insects for death and/or reduced growth. These include miticides targeting mites (arachnids) typically applied to other animals (insects and mammals).


Second – Let’s Name Names!

There are some widely used chemicals that are quite frankly – KILLING US! They are bad for the environment, they are bad for bees, they are bad for us.  Sadly, they are also still widely used, especially in the US.

Here, we have highlighted only TWO of the WORST of the WORST (WOTWO, pronounced WHAT-whoa) chemicals– GLYPHOSATE & NEONICOTINOIDS. Technically, neonicotinoids (or neonics) are a class of chemicals so there are MANY different chemicals in this category.

Below we lay out how these chemicals are bad for bees, and how they are bad for the environment. Do yourself + your bees a favor – STOP using these WOTWOs!

WOTWO Chemical #1: GLYPHOSATE

What Is It? HERBICIDE

Commonly Known As: Roundup, Enlist Duo

This image has been altered to reflect the more accurate impacts of the active ingredient, glyphosate, which has been scientifically shown to cause harm to bees, humans, and the environment.

How Does Glyphosate Impact Honey Bees?

  1. reduces foraging success
  2. impairs memory & learning
  3. disrupts gut microbiome
  4. depresses immune system by inhibiting essential amino acid synthesis
    • targets the shikimate pathway – plants & many microbes use this pathway to biosynthesize 3 key amin0 acids: tryptophan, tyrosine & phenylalanine
      • IMPACTS to PLANTS: these 3 amino acids are backbones of aromatic compounds used by plants for defenses
        • these plant defenses are called secondary metabolites, which plants use as defenses against being eaten by herbivores
      • IMPACTS to BACTERIA: this biosynthesis pathway is also used by gut bacteria to provide essential amino acids assimilated from things in the diet
      • IMPACTS to HIGHER ORGANISMS (like HUMANS): these are listed as essential amino acids that are required through diet since most higher organisms cannot synthesize them

How Does Glyphosate Impact the Environment?

  1. Soils treated with glyphosate had higher loads of fungal plant pathogens.
  2. Residual time in soils lasts years, and builds up over repeated uses.
  3.  Soil microbial diversity declined in soils exposed to glyphosate.
  4. Glyphosate interferes with essential nutrient uptake in crop plants & disrupts nitrogen-fixation.
  5. Causes DNA mutations in Earthworms.
  6. Decreased plant diversity in landscapes neighboring crops due to exposure from drift.
  7. Monarch declines are linked to use of glyphosate on GM corn, which nearly eradicated all native milkweed species (their sole host plant for caterpillars).
  8. Glyphosate was found in nearly 30% and the breakdown product was found in over half of all surface waters tested.
  9. World Health Organization (WHO) has listed glyphosate as a potential carcinogen.

For more details on how GLYPHOSATE impairs honey bee health and the environment, you can read the studies HERE and HERE


WOTWO Chemical #2: NEONICOTINOIDS

What Is It? INSECTICIDE

Commonly Known As: Imidacloprid, Clothianidin, Thiamethoxam, Acetamiprid, Dinotefuran

List of common neonicotinoid garden products sold in the USA and their active neonicotinoid chemical, how they work, and the names sold under for commercial products. Table source: http://xerces.org/sites/default/files/2018-05/16-009_02_XercesSoc_Protecting-Bees-From-Neonicotinoids-in-Your-Garden_web.pdf

How Do Neonicotinoids Impact Honey Bees?

  1. impairs foraging success
  2. delays brood & larval development
  3. impairs memory & learning
  4. damages the central nervous system
  5. increases susceptibility to diseases
  6. causes significant loss of hygiene
  7. some neonics are 5,000 -10,000x more toxic to bees than DDT
  8. neonics are as addictive to bees as nicotine is to humans

How Do Neonicotinoids Impact the Environment?

  1. About 5% of the active ingredient is taken up by crop plants, most leaches into the environment.
  2. Non-flowering crops treated with neonics risk non-target organisms through increasing mortality in beneficial predator populations.
  3. Can persist in ag soils for years, leading to chronic contamination & accumulation over time.
  4. Found in a most waterways – ditches, puddles, ponds, mountain streams, rivers, temporary wetlands, snowmelt, groundwater & water treatment outflows.
  5. Aquatic insects are several orders of magnitude more sensitive to neonics than the model organisms used in pesticide regulatory assessments.
  6. Found in pollen, nectar & foliage of non-crop plants next to ag fields exposing non-target insects & non-bee pollinators in pollinator conservation areas.
  7. Use in ag areas was negatively correlated with population metrics for butterflies, bees and insectivorous birds across 3 countries.
  8. Migratory birds died from eating insects exposed to neonics applied to a crop – an example of detrimental & unintended impacts up the trophic cascade.

Graphic depicting how neonicotinoids impact non-target organisms, like birds and beneficial insect pollinators. Source: http://www.beyondpesticides.org/programs/organic-agriculture/eating-with-a-conscience?pid=610

For more details on how NEONICOTINOIDS impair honey bee health & the environmental impacts, you can read more HERE, HERE, HERE, and HERE.


Futurama: WOTWO Chemicals Replaced with Biotechnology?

The solution to this problem could be as simple as no longer using and manufacturing these WOTWO chemicals. Yet this would require a cold-turkey cut off from chemical applications replaced with what? Organic farming practices? I WISH!

But alas, Big Ag is the elephant in the room, as they are driving both the chemicals and the alternatives to them. Science has stepped into the fray by providing an alternative to changing our behaviors – another option now is on the horizon, thanks to mRNA technology!

RNAi INSECTICIDES

This is a newer technology, and several mega-corporations (Bayer, BASF, Syngenta) have pushed to bring them to market fast.  In RNAi-based crop protection, insecticidal double-stranded RNA (dsRNA) is taken up by the target organism (often called ‘pest’) through ingestion of the material (typically plants) and subsequently directs the degradation of specific, targeted messenger RNA (mRNA) inside the host target. Degradation of this mRNA prevents the synthesis of essential proteins in the organism (pest), resulting in reduced growth or mortality.

RNAi technology is a ds RNA biocontrol which can be sprayed onto the plant. It gets taken up into the targeted “pest” insect when the insect feeds on the plant. Ideally, in theory it is specific for a target organism, so it does not harm non-target insects, pictured here as the beneficial honey bee. Once inside the target insect cells, it triggers the RNAi process, which prevents essential proteins from being produced. This ultimately controls the insect before it can become a pest to the plant. The plant can then complete it’s life cycle providing safe resources to the beneficial insects and other consumers up the trophic chain.
Replicated from . M. Bramlett, G. Plaetinck and P. Maienfisch, RNA-Based Biocontrols—A New Paradigm in Crop Protection, Engineering,https://doi.org/10.1016/j.eng.2019.09.008

  1. What is RNAi?
    • RNA interference = post-transcriptional sequence-selective gene silencing
    • RNAi  i = interference refers to the cellular mechanism (HOW IT WORKS)
    • RNAi  i = insecticide refers to the ecological function (WHAT IT DOES)
  2. How does it work?
    • Small RNA fragments bind to mRNA, the workhorse making proteins for cell functions
    • Binding then promotes cleavage on mRNA
    • Cleavage of mRNA reduces gene expression – no proteins made = no WORK done!
    • Plants, fungi, & 1 animal (nematode) naturally do this to combat viruses.
  3. How does insecticidal RNAi differ from RNAi used in the natural world by plants & fungi?
    • Insecticidal RNAi silences specific genes
    • Insecticidal RNAi  is designed to overcome natural cellular defenses that destroy small RNAs
    • Insecticidal RNAi is designed as small + well defended molecules that kill higher organisms
    • Natural RNAi evolved to combat viral infections in plants & fungi
  4. Are there adverse impacts of insecticidal RNAi?
    • Can silence unintended genes in target organisms: this shuts down wrong genes in the bug you wanna kill & doesn’t work!
    • Can silence target genes in non-target organisms: this shuts down correct genes in WRONG organism, like beneficial pollinators!
    • Can stimulate the immune system in non-target higher organisms: this creates a trophic cascade triggering immune defenses in higher animals.
    • Residuals remain in soils, requiring uptake by microbes to break it down.

So What To Make of RNAi Technology?

RNAi technology is likely to be what replaces wide-spread and chronic use of chemical pesticides in agriculture. But before it replaces it, we are more likely to see it added into the cocktail in GM crops. This technology is typically applied to plants and/or to soil to target various insects considered as pests, but it can be applied to feed for beneficial insects being parasitized by fungal or viral infections. A promising study by the USDA showed this RNAi technology could be fed to honey bees in sugar syrup to successfully rid them of Nosema cerana infection, a microsporidia that targets the gut of the bee and rapidly kills honey bee colonies if left untreated.

What we still do not have enough information about are the impacts to the environment with long-term, chronic, habitual and wide-spread use – similar to the use of WOTWO chemicals GLYPHOSATE & the class of NEONICOTINOIDES that this technology is likely to replace. Due to the highly specified nature that each RNAi insecticide will have, we need robust, complete and transparent research into the impacts on non-target organisms. And preferably not by scientists that are funded and/or work for some of these Big Ag corporations – which I do have linked in my sources, too.

One of the problems is rather than replacing the wide-spread use of chemicals in agriculture, the technology is being added to existing GM plants. The biggest players in the RNAi game are mega-corporations with deep pockets interested in capitalizing on adding RNAi into their cocktails, rather than replacing things like RoundUp Ready genes. We must use caution when applying ANY technology across wide swaths of our landscape before we approve for wide public use, and each one of these RNAi insecticides will need to be tested before released to market.

That being said, the first RNAi corn already hit the market. Are you shocked? Well, the EPA approved it back in 2017 in a very quiet manner, so you might already be eating it – Dow-Monsanto added the gene into their GM corn cocktail, sold as SmartStax, which now contains 8 modified genes. Corn is not the only food getting the RNAi treatment, others like soybean and cotton are coming soon. Using RNAi technology, Monsanto has enhanced the oil profiles of soybeans, while Intrexon has made non-browning apples. Other food items made with RNAi include decaffeinated coffee, non-allergenic peanuts, and nicotine-free tobacco.

For more information about this emerging new technology, you can read more HERE, HERE, HERE, HERE, HERE, and HERE.

If you are looking specifically for more information on the safety of this new technology on humans and vertebrates, read more HERE.


Works Cited

Sources: Pesticides in General

Pettis JS, Lichtenberg EM, Andree M, Stitzinger J, Rose R, et al., 2013. Crop Pollination Exposes Honey Bees to Pesticides Which Alters Their Susceptibility to the Gut Pathogen Nosema ceranae. PLoS ONE 8(7): e70182. doi:10.1371/journal.pone.0070182

Wu, Anelli & Sheppard, 2011. Sub-Lethal Effects of Pesticide Residues in Brood Comb on Worker Honey Bee (Apis mellifera) Development and Longevity. PLoS ONE 6(2): e14720. doi:10.1371/journal.pone.0014720.

Sources: Glyphosate

Herbert et al., 2014. Effects of field-realistic doses of glyphosate on honeybee appetitive behaviour. J Exp Biol 217:3457-64. doi: 10.1242/jeb.109520

Motta, Raymann & Moran, 2018. Glyphosate perturbs the gut microbiota of honey bees.https://www.pnas.org/content/pnas/early/2018/09/18/1803880115.full.pdf

Sources: Neonicotinoids

Arce, et al., 2020. Foraging bumblebees acquire a preference for neonicotinoid-treated food with prolonged exposure. Proceeding of the Royal Society-B 285: 20180655. http://dx.doi.org/10.1098/rspb.2018.0655

Hallman, et al. 2014. Declines in insectivorous birds are associated with high neonicotinoid concentrations. Nature doi:10.1038 nature13531. https://www.nature.com/articles/nature13531/

Wood & Goulson, 2017. The environmental risks of neonicotinoid pesticides: a review of the evidence post 2013. Environ Sci Pollut Res Int 24(21): 17285–17325 doi: 10.1007/s11356-017-9240-x

Sources: RNAi

https://www.oecd.org/chemicalsafety/pesticides-biocides/conference-on-rnai-based-pesticides.htm

Bramlett, M., G. Plaetinck and P. Maienfisch. 2019. RNA-Based Biocontrols—A New Paradigm in Crop Protection, Engineering, https://doi.org/10.1016/j.eng.2019.09.008

Huang, Q., Li, W., Chen, Y., Retschnig-Tanner, G., Yanez, O., Neumann, P. and Evans, J.D. 2019. Dicer regulates Nosema ceranae proliferation in honeybees. Insect Mol Biol, 28: 74-85. https://doi.org/10.1111/imb.12534

Mogren C.L., Lundgren J.G. 2017. In silico identification of off-target pesticidal dsRNA binding in honey bees (Apis mellifera) PeerJ 5:e4131 https://doi.org/10.7717/peerj.4131

Rodrigues, T. B., Petrick, J. S. 2020. Safety Considerations for Humans and Other Vertebrates Regarding Agricultural Uses of Externally Applied RNA Molecules https://www.frontiersin.org/articles/10.3389/fpls.2020.00407/full

SzékácsA., Mendelsohn, M.L. 2021. Editorial: RNAi Based Pesticides, Frontiers In Science, https://www.frontiersin.org/articles/10.3389/fpls.2021.714116/full

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