More research shows neonic pesticides compromise bee immunity

Our Nation’s bees are in a tail spin, and victims include commercial honey bees, wild bumble bees, and other native bee species.  This isn’t just a bee problem – it’s our problem too because we rely on the pollination services of our buzzing invertebrate friends to grow food and make flowers bloom. According to the US Department of Agriculture Honey Report, honey production is down, as it has been almost every year since the neonicotinoid pesticides were approved (see graph below from Dr. Susan Kegley, Pesticide Research Institute). Honey production.jpg

The decline of bee colonies almost certainly has numerous causes.  Much of the pesticide industry is focused on pathogens like Nosema parasites and Varroa mites, shifting attention away from their own harmful pesticide products. But, science is bringing pesticides and bee deaths closer together. 

It is now evident that even low field-realistic levels of neonicotinoids (‘neonics’) – a class of pesticides purposely designed to soak into the whole plant – are compromising the immunity of bees, leaving them unable to fend off viruses and other deadly pathogens that stress and eventually kill bee colonies. It is a deadly one-two punch. The bees are immune compromised from the pesticides, and then fall prey to mites and other viruses that kill them.

A new study (Di Prisco et al 2013) suggests a mechanism for how these neonics are compromising bee immunity. Researchers exposed honey bees to clothianidin – a neonicotinoid pesticide commonly used as a seed treatment and to spray on field and tree crops, turf, and ornamental trees and flowers - and then infected the bees with a virus. Compared to unexposed (control) bees, the pesticide neonic bees had reduced immune system function and impaired signaling of a molecule called “NF-kappa B” (NF-kB), normally required for proper function of the immune system. Interestingly, when chlorpyrifos, an organophosphate pesticide that shares a mechanism of toxicity with the neonicotinoids, was tested under the same conditions its effects on immune response were negligible, suggesting this toxic mechanism may be specific to the neonic pesticides.

This research supports the findings of earlier studies.  US Department of Agriculture chief scientist Dr. Jeff Pettis and his research collaborators at Penn State University reported in 2012 that honey bees born and raised in hives with low sub-lethal levels of neonicotinoid pesticides had a significantly higher risk of infections of the deadly gut parasite Nosema.

And an earlier study found that imidacloprid – a neonicotinoid used as a seed treatment and to spray field and tree crops and ornamental plants, trees, and turf – when coupled with the Nosema parasite resulted in more bee deaths than either the pesticide or the parasite alone (Alaux et al 2010). This study used field-realistic levels of imidacloprid, at 0.7, 7, and 70 parts per billion (ppb).

In addition to immune system damage, a handful of well-conducted studies on honey bees and bumble bees suggest that bee colonies exposed to field-realistic levels of neonic pesticides in small but repeated or lasting (several weeks) doses have significant behavioral and functional impairments such as impaired learning, food collection, navigation, immune function, and reduced fecundity and queen production. While not likely to cause immediate (acute) death, such abnormal behavior can hinder the ability of the colony to survive winter. (See the Xerces Society report and my blog here for details).

The neonic pesticides were developed to replace the highly acutely toxic war-era organophosphate (OP) pesticides that were not only highly toxic to bees, but also responsible for fish kills, bird kills, farmworker poisonings, poisoning of children from residential uses, and even long-term neurological impairments to the children born in the womb to exposed mothers.(see my blog here for details)

However, the systemic neonic approach has two major failings that make these pesticides potentially even more dangerous to pollinators and other beneficial insects than the OP pesticides that they replaced. First, their use undermines the principles of Integrated Pest Management (IPM) which requires that pesticides only be used if they are needed, and then only where they are needed, and in the least amount possible to be effective. ‘Use only when needed’ is important to reduce the development of pesticide-resistant pests.  Systemic pesticides are the opposite of IPM – they are prophylactic and unavoidable by design. Second, whereas the OP pesticides could be avoided by not spraying when bees are foraging (a label requirement), the neonics cannot be avoided because all the components of the plant – and particularly the pollen, nectar, and guttation drops – carry the pesticide at measurable levels.

These problems combined with the accumulating evidence that neonics are likely a significant factor in recent bee declines means that it’s time to reconsider the now pervasive use of these pesticides.

Recent research by USDA scientist Jeff Pettis found 35 different pesticides in bee pollen in addition to neonics that appear to weaken the immunity of bees, leaving them unable to fend off the viruses that eventually kill them. (Pettis et al 2013)

Many landscape and ornamental  trees or flowering plants for homes and gardens are pre-treated with neonicotinoid pesticides, often at levels are exceeding those used in agriculture. Friends of the Earth US (FoE US) and the Pesticide Research Institute (PRI) issued an important report in August 2013 called, Gardeners Beware: Bee-toxic pesticides found in bee-friendly plants sold at garden centers nationwide. The report found that 54% of garden plants purchased from major retailers (including Lowes and Home Depot) contained system neonicotinoids at levels that could harm bees. Since the plants are not labeled consumers have no way of knowing that their garden may poison bees, so ask your retailer and let them know that you won’t purchase bee-poison plants.

The “Saving America’s Pollinators Act of 2013” was introduced into Congress by Representative John Conyers, Jr. (D-Mich.) and Representative Earl Blumenauer (D-OR). The Act directs EPA to suspend use of the most bee-toxic neonicotinoids for use in seed treatment, soil application, or foliar treatment on bee attractive plants within 180 days – with some exceptions - and to review these neonicotinoids and make a new determination about their application and safe use. If this Act passes Congress it will certainly be a big step in the right direction to protecting pollinators.

About the Authors

Jennifer Sass

Senior Scientist, Health program

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