Researchers say neonicotinoids not solely responsible for honeybee deaths

European Honeybees are thought to be a bit more tolerant to certain pesticides than bumblebees, according to university researchers.

Neonic debate seeks to sift bad science from good

Colony Collapse Disorder first coined in 2006 Imidacloprid thought to be most lethal neonicotinoid to bees Researchers, beekeepers believe cause of bee decline is complex and multifaceted

As answers remain forthcoming on the toxicity of neonicotinoids to pollinators a mix of scientists and regulators recognize the need for more university research into potential causes of bee deaths know more commonly as colony collapse disorder (CCD).

A recent seminar at UC Davis set out to address the “truths and myths” of neonicotinoids and their impacts on pollinators.

If there was anything to come from the day-long seminar, it was summed up succinctly by the university’s extension apiculturist, Elina Lastro Niño.

“What I’ve learned and what is obvious from all of this is it’s a complicated topic and situation,” Niño said. “It’s not just pesticides in general or neonics specifically that are responsible for colony collapse disorder.”

Just what is responsible for declining bee health? Experts do not fully understand.

While researchers seek answers to what was first seen about 2004 and coined about two years later as CCD, hyperbole continues to spread, and not just through popular media sources; sadly, some scientific research papers have been chastised by other researchers for their “bad science.”

What are Neonicotinoids?

According to Texas A&M Extension, neonicotinoids are a class of insecticides chemically related to nicotine. The name literally means “new nicotine-like insecticides.” Like nicotine, the neonicotinoids act on certain kinds of receptors in the nerve synapse.

Because neonics are much more toxic to invertebrates, like insects, than they are to mammals, birds and other higher organisms, attention has focused on them as the chief cause for CCD. The phrase has become a catch-all for what are really the unexplained deaths of bee colonies in the United States, Canada and Europe.

Neonicotinoids come under a variety of names or active ingredients, including: Acetamiprid, Clothianidin, Dinotefuran, Imidacloprid, Nitenpyram, Thiacloprid, and Thiamethoxam.

It’s the accusation that neonics are the primary cause for CCD that has the companies using and selling these products on the defensive. Some like The Home Depot and Scotts are looking to either reduce or eliminate neonics from their shelves and product line-ups.

Honeybee impacts

While the debates continue to be quite animated university researchers say there remains a lack of conclusive evidence that neonics are the sole cause of declining bee health, yet they do not discount the class of insecticides as being at least partially responsible for declining bee health issues.

According to UC Davis Ph.D. candidate Margaret Scampavia, 75 percent of university studies looking into the effects of neonics on pollinators focus on one species – the European Honeybee. Nineteen percent of the studies look at the estimated 250 species of bumblebee. The rest of the studies are scattered across over 20,000 species of wild bees.

Scampavia, who studies in the Department of Entomology and Nematology at UC Davis, used this to illustrate how little is known about the widespread impacts of neonics on other insect pollinators.

What is suspected, according to research Niño and Scampavia highlighted during their discussions, is the numerous potential causes of bee health issues.  Habitat loss and fragmentation, genetics, nutrition, invasive species, climate change, parasites, overwintering and pollination stress, pesticides and pathogens are said to all play a role in affecting bee health, according to the two UC Davis researchers.

Some of these impacts may even be interconnected, they said.

Beekeeper perspective

Gene Brandi is the vice president of the American Beekeeping Federation and a commercial beekeeper in central California who manages about 2,000 bee colonies. He’s seen first-hand mass die-offs of his bee colonies through the application of pesticides and through more mysterious means.

Brandi spoke at the UC Davis symposium, agreeing that more research is needed into the cause of CCD, a phrase he admits he does not care to use.

“I don’t really like the term CCD because it kind of denotes the picture that there’s really just one thing wrong here, that if we could just fix this one thing then everything would be just wonderful,” Brandi told an audience of several hundred.

Still, Brandi believes that “pesticides are most certainly an issue” in CCD.

Brandi has been a commercial beekeeper since the 1970s. In that time he’s seen his colony losses during the winter climb from under 5 percent to upwards of 45 percent. He says he is fortunate today if his queen bees survive a year when they used to last upwards of two years or sometimes longer.

Having to replace queen bees one or two times per year gets costly at $21 to $22 per queen, Brandi says.

Brandi suspects that there are causes outside of direct pesticide contact that could be prematurely killing his bees. The Varroa mite is just one of these known causes. These tiny parasites vector diseases that can kill honey bees.

Drought is another factor he blames for declining bee health.

Brandi’s experience with neonics includes foliar applications on a variety of crops, including those that bees tend not to frequent, though he suspects could have a role to play in his bee deaths.

Brandi recently experienced a bee kill from the use of Dinotefuran on tomatoes and has seen similar issues with Clothianidin, Imidacloprid and Thiamethoxam in cotton.

He praises the label removal of Imidacloprid from almonds as much of the nation’s honeybee population is needed each year to accommodate almond pollination. Current research suggests of all the neonics out there, Imidacloprid is the most toxic to honeybees.

Brandi shared the story about an issue he had in melons over the course of several years. After watching about 1,000 colonies of honeybees not overwinter well after coming out of the melons he began looking into the issue with the farmer.

On the surface the farmer was doing things right. Pyrethroids were sprayed only at night when the bees weren’t flying, yet he continued to lose about half the bees used in melons during the winter months.

“I didn’t know until about the fourth or fifth year that they were chemigating with Imidacloprid through their subsurface drip, and I had about 1,000 colonies on this ranch,” Brandi said.

Brandi no longer pollinates for that ranch.

“Bees can pick up pesticides through nectar or water … and I can guarantee you that on the west side of the San Joaquin Valley the only water available for bees to drink is irrigation water. There is just no other water available for them.”

It is sub lethal impacts of pesticides like this that concern Brandi because they can be lethal to the entire colony. Spray drift is another concern for Brandi.

Some of the effects Brandi has seen include damage to queens, drones and the brood. He has also seen changes in adult bee behavior, which is detrimental to individual bees and entire bee colonies.

Among the other things concerning to Brandi include the length of time neonics can remain toxic to bees after an application, and the use of neonics as seed treatments in certain crops.

Scampavia pointed to several research studies that suggest how neonic-treated seed can be lethal to bee colonies.

Early research

According to Scampavia, bumblebee declines have been reported in four of the eight U.S. species and in six of the 16 United Kingdom species. Three U.K. bumblebee species are now extinct.

Because of bee declines in Europe, the European Commission issued a two-year restriction on certain applications of Clothianidin, Thiamethoxam and Imidacloprid to allow time for scientific research to catch up with neonic use, Scampavia said.

What is generally known, according to Scampavia, is there are two basic routes of pesticide exposure in bees: oral and contact.

Of the seven neonics listed – Imidacloprid, Clothianidin, Thiamethoxam, Dinotefuran, Nitenpyram, Acetamiprid and Thiacloprid – Imidacloprid is said to be most toxic to honeybees. Thiacloprid is said to be the least toxic to honeybees based on 24 hour LD50 figures.

The LD50 figure is the standard of measure used to determine the toxicity of a product wherein a product, when given all at once, causes the death of 50 percent of a given population within 24 hours.

For honeybees, the LD50 number for Imidacloprid is 18 nanograms per bee. That number climbs to 15,000 ng/bee for Thiacloprid, meaning it is less toxic to honeybees.

According to Scampavia, 78 percent of research has focused on Imidacloprid toxicity to honeybees.

Some of those studies suggest that a single, acute dose of Imidacloprid can impair learning, motor activity and memory in honeybees, whereas chronic, sub lethal doses can impair learning and foraging.

Study results start to break apart in several areas, she said.

For example, there is a high variability between studies relating to the oral toxicity of neonics. Furthermore, some studies fed bees levels of neonics much greater than what are widely considered to be “field-realistic” levels of pesticide residue.

Still others like Michael Parrella, professor and chair of the Department of Entomology and Nematology at UC Davis, and James Bethke, nurseries and floriculture farm advisor for the University of California Cooperative Extension, recognize that “bad science” exists, which remains “a big problem,” according to Parrella.

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