Industry Perspective: Systemic Insecticides And Bees: Are We Revisiting “Silent Spring”?

Greenhouse Tomato BeesEditor’s Note: The author is currently evaluating neonicotinoid systemic insecticides’ efficacy against phloem-feeding insects and says he hopes to have study results available next year. Research on neonicotinoids and bees is a potential project on the horizon.

Recently, there have been concerns associated with the potential direct and indirect effects of neonicotinoid systemic insecticides on bees. The neonicotinoid systemic insecticides include imidacloprid, thiamethoxam, dinotefuran, clothianidin and acetamiprid. These active ingredients are present in many products available to both professionals and homeowners. The concern is affiliated with exposure from foliar applications and exposure to pollen and nectar that may be contaminated via applications to the soil or growing medium. These insecticides have a higher selectivity for insects compared to mammals than other insecticides in the chemical classes organophosphate and carbamate. The mode of action of a neonicotinoid is as an agonist at an insect’s nicotinic acetylcholine receptor. (An agonist is a chemical that binds to a receptor and activates the receptor to produce a biological response.)

The specific proposed benefits of any systemic insecticide (not just neonicotinoids) includes:

  • plants are generally protected throughout most of the growing season without the need to make repeat applications
  • minimal issues regarding drift (when applied as a drench or granule) compared to foliar applications of insecticides
  • less direct impact on natural enemies and bees

Despite these benefits, there have been many sound scientific studies conducted, although primarily under laboratory conditions, that have demonstrated both lethal (direct mortality) and sub-lethal (affecting reproduction and/or survival) effects associated with neonicotinoid systemic insecticides on honey bees and bumble bees.

Missed Opportunities For Education And Outreach

Ultimately, this entire issue regarding the concern of how neonicotinoid systemic insecticides may directly and indirectly affect bees is related to two factors. One is the Oregon incident that occurred in June 2013 in which a landscaper sprayed 55 blooming European linden trees with dinotefuran (Safari) for control of aphids. The use of the insecticide was mainly as a contact and ended-up killing approximately 55,000 bumble bees in a Target parking lot in Wilsonville, Ore. However, the label states specifically, “This product is highly toxic to bees exposed to direct treatment or residues on blooming crops or weeds. Do not apply this product or allow it to drift to blooming crops or weeds if bees are visiting the treatment area.”

What should have been a great outreach opportunity to educate people on the importance of reading the label was twisted into a means to promote the banning of neonicotinoid systemic insecticides. It is difficult to understand why the Oregon Department of Agriculture did not stress the point regarding the off-label use more. In fact, the landscaper was fined a modest $555 for killing 55,000 bumble bees and not reading the insecticide label. What is wrong here?

The second instance was related to a 2013 publication, Gardeners Beware: Bee-Toxic Pesticides Found In “Bee-Friendly” Plants Sold At Garden Centers Nationwide, by the Friends of the Earth. The publication was based on an extremely poorly constructed preliminary study regarding the sampling of nursery plants treated with neonicotinoid systemic insecticides from three locations (California, Washington, D.C. and Minnesota). Overall, this study demonstrated nothing, especially since the study failed to quantify the concentration of active ingredient in the pollen and nectar (they simply combined leaves, stems and flowers). Furthermore, only seven out of 13 (54 percent) of the plants sampled (tomato, squash, salvia, gaillardia, pumpkin, zinnia and aster) tested positive for one or more neonicotinoid insecticides.

No general inferences can be justifiably made on the impact of neonicotinoid systemic insecticides on bees. However, this information was accepted as demonstrating that ornamental plants treated with neonicotinoid systemic insecticides are toxic to bees. So, this represents another instance of misinformation or lack of substantial reliable information.

It is important to remember that the impact of systemic insecticides (non-neonicotinoids) on bees and other pollinators is not a new phenomenon. Below are three publications from studies that demonstrated the direct impact of certain systemic insecticides on bees.

  1. Glynee-Jones, G. D., and W. D. E. Thomas. 1953. Experiments on the possible contamination of honey with schradan. Ann. Appl. Biol. 40: 546-555.
  2. Jaycox, E. R. 1964. Effect on honey bees of nectar from systemic insecticide-treated plants. J. Econ. Entomol. 57: 31-35.
  3. Lord, K. A., M. A. May, and J. H. Stevenson. 1968. The secretion of the systemic insecticide dimethoate and phorate into nectar. Ann. Appl. Biol. 61: 19-27.

What Will Banning Neonicotinoids Accomplish?

One question that needs to be addressed is — will the banning of neonicotinoid systemic insecticides in actuality preserve bees? In all likelihood, producers and homeowners are going to use contact insecticides such as carbaryl (Sevin) and pyrethroid-based insecticides as sprays on a frequent basis, which in the long-term will be more detrimental to bees than systemic insecticides. In addition, there could be problems associated with pesticide drift, direct and indirect effects on natural enemies (e.g., parasitoids and predators), issues affiliated with residues on leaves and flowers and the potential for insecticide resistance due to the selection pressure placed on insect and mite pest populations.

Currently, the emphasis has been on the neonicotinoid systemic insecticides; however, what about other systemic insecticides such as acephate (Orthene), disulfoton (Di-Syton), and dimethoate (Cygon) that are still commercially available to homeowners, although both disulfoton and dimethoate have been or are being phased-out? And what about chlorantraniliprole (Acelepyrn) and spirotetramat (Kontos)? Will these be the next targets?

Professionals and homeowners can utilize pesticides without harming bees by using selective products (e.g., Dipel) with short residual activity, time applications accordingly when bees are less active, such as the early morning or evening, and use plants in landscapes and gardens that are less susceptible to pests.

Important Questions And Ideas That Must Be Considered

Below are a number of general comments and questions regarding neonicotinoid systemic insecticides that need to be taken into consideration:

  1. Can neonicotinoid systemic insecticides (NSI) be absorbed into plants and become present in pollen and nectar, thus making floral resources toxic to bees?
  2. Are NSI present in pollen and nectar at concentrations that cause lethal or sub-lethal effects?
  3. Will exposure via pollen and nectar result in lethal, sub-lethal effects or no effects?
  4. Can NSI contaminate or accumulate in weeds and/or wildflowers?
  5. Exposure to contaminated pollen and nectar may increase honey bee susceptibility to parasites and pathogens by compromising the immune system.
  6. What about interactions and multiple factors? For example, what about the effect of combination products and interactions with fungicides?
  7. What about timing of application? In general, and based on scientific research, residues of the active ingredient may occur at higher levels in pollen and nectar when applications are made before or during bloom.
  8. What about the effects of the metabolites, which tend to be more toxic to insects, associated with the NSI?

Some of the points mentioned above have been demonstrated based on scientific research. Furthermore, there are numerous factors that may influence variation in residue levels in pollen and nectar including timing of application, application method, application rate, number of applications (carry-over effect), formulation, water solubility, plant type and flower morphology, plant age and size, soil type and organic matter content, environmental conditions (e.g, light intensity) and bee age and size. This clearly highlights the complexity of the issue.

Also, it should be noted that honey bees can travel four miles from a hive, and they typically gather nectar and pollen from a wide-range of flowers (in fact, the primary food source of the European honey bee is clover and alfalfa) during the season, thus possibly diluting “contaminated” pollen and nectar by collecting from different flowers.

We need to be aware of the direct and indirect impact of all pesticides (e.g., insecticides, miticides and fungicides) on bees. Furthermore, it is critical to read the label of any pesticide to determine if there are any effects on bees.

We also have to understand that there is no clearly defined “smoking gun” because many factors may be contributing to bee decline globally, including parasites such as the varroa mite (Varroa destructor), pathogens (e.g., Nosema cerane), loss of habitat, nutritional deficiencies, habitat fragmentation, intense management strategies (bee feedlots), poor beekeeping and pesticides.

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10 comments on “Industry Perspective: Systemic Insecticides And Bees: Are We Revisiting “Silent Spring”?

  1. I’m glad to see that we finally have some people doing sound research that will offer better information regarding the use of these chemicals. We all want to protect our environment and this will help us make sound decisions regarding the use of any pesticides..

  2. Very good summary of the situation with this pesticide family. As so often happens these days, individuals or organizations have an agenda and look for anything that will support their “side”. The results are so-called “bumper-sticker” (i.e. simplistic) responses to complex problems. There’s almost always more to the story, as research has shown. Good luck in trying to help sort some of this out.

  3. Great article! The University of Florida Bee College and the State of Florida Department of Plant Industry DPI give day long hands on workshops to hundreds of interested enthusiasts throughout the year at county extension offices. According to the college and DPI there are NO incidences of CCD Colony Collapse Disorder outside of commercial honey producers. Commercial producers truck hives to Florida from 26 states in the winter and the stress of the move combined with the increase of parasites inherent with the widely used imported Italian Honey Bee Queens and poor beekeeping practices are thought to be the primary causes of CCD. With honey prices on the rise and better management, CCD might be on the wane but the cat is out of the bag with pesticides and bees in the media. Just like they know that Poinsettias are poisonous.

    1. Another problem of migratory beehives is that it helps spread pathogens among hives. Despite all the noise about CCD, the varroa mite continues to be the single worst killer of honey bees.

  4. I am impressed about the well rounded and fact based article that shows many different sides of the argument without the PR bias that exists far too often. I am stunned about a fine of $555 for mis-use of a pesticide by a “professional”. I am concerned that all neonicotinoid are being lumped together as the class is as varied as annual plants

    Thanks for the article!

  5. I truly feel that trying to make this whole topic more complicated than it is leads to.. well..confusion The facts as I see it are now plain and in sight, this group of chemicals has been proven to be lethal to our honey bees and like it or not, the honeybee is now part of our ecosystem, both here in North America and in Europe. We need to now be working tirelessly to come up with viable, sustainable,and SAFE alternatives. I have been involved in commercial horticulture since the mid 1980’s and do not feel proud that parts of industry relies on some of these chemicals.

    1. Please, don’t forget all the native pollinators. Honey bees are not part of the ecosystem in North America, but the much ignored native bees are. They do more pollination than they get credit for and are more vulnerable to pesticides because they are not protected. At least a beekeeper can move the hives to a safe place when pesticide applications are going on. Almond fields are sprayed relentlessly after the hives are gone and this destroys all native bees and other beneficial insects.
      Despite all this, 40% of crop pollination in California is done by native bees.

  6. Considering the sorry state of government funding for Ag Research and Ag Extension, researchers now have to constantly scramble for any available funding. A significant amount now comes from the major Ag chemical companies, which leads to the best research money can buy. More public money needs to be invested. Do think that economic poisons need to be seriously restricted from home garden use.

  7. Hey Ray,

    Good article. I cannot believe that Disyston and Cygon are :
    1. Available and labeled for homeowner use
    2. Still on the market
    We stopped using organophosphates years ago and it just scares me the damage homeowners can do.

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