The multiple effects of crop chemicals – herbicides, pesticides and fungicides – remain some of the most visible and, coincidentally, some of the most poorly covered players in the worldwide decline of honey bee populations.
There are other factors in play as well. Forage losses, diseases and transport stress are three other reasons why world governments and local orchard and grove owners are concerned about the fate of bees.
Forage loss is a significant problem. The continued conversion of farmland and open space into commercial and residential uses has significantly reduced bee pastures. Flowers are also less available, due to state practices of spraying back rights-of-way to reduce the risk of fire.
Any solution to this problem must be long-term. Since land-use and right-of-way maintenance policies are handled by states, change will come slowly.
Whatever the reason, the numbers don’t lie. For the last seven years, just as those in the rest of the world, the U.S. bee population has been in steep decline.
An acceptable over-winter colony loss rate is 15 percent. In the U.S., over-winter losses in 2012 and 2013 ran around 30 percent. Last winter, losses dropped to just over 23 percent.
Any celebration would be premature. While average losses last year were lower, there are quite a few states that continue to suffer heavy winter losses. There are also more than a few entomologists who would say annual losses are far more significant than winter losses.
“It is clear bees are dying all year long,” said Reed Johnson, an Ohio State University research entomologist. “Our annual losses are nearly 50 percent.”
Many entomologists now feel colony collapse disorder is an overrated threat. It is responsible for only 7 percent of U.S. annual bee population losses.
The popular press has focused attention on pesticide exposure as a principal culprit in bee population declines. Although there is some substance to this concept, the scientific community is unable to determine exactly how serious the threat is.
Assigning risk has been hampered by an inability to measure it with a large degree of accuracy.
“No one has been able to nail a standardized protocol useful for risk assessment,” Johnson said.
The only widely accepted risk assessment tool is known as LD50. Scientists expose a group of bees to low, medium and high doses of a pesticide. Over a 48-hour period, the test determines the dose at which 50 percent of the bees in the test group will die.
Johnson describes LD50 as “a conservative tool.” When dealing with compounds requiring medium or high application rates, field studies are a much better way to go.
Additionally, death by direct contact is a less serious threat than what entomologists refer to as “sub-lethal dosage.” Instead of killing bees outright, this kind of exposure weakens them to the point where they are far more susceptible to disease over a longer period of time.
“When bees are exposed to pesticides, their detoxification processes use a considerable amount of the bees’ energy to reduce the threat,” said Eric Mussen, a UC-Davis Extension apiculturist.
Chris Mullen, a Pennsylvania State University entomology researcher, feels surfactants represent a significant toxic risk to bees. Materials used to decrease the surface tension in liquids; surfactants increase the surface area liquid applications cover on plants.
“There are lots of formulations of these chemicals,” said Mullen. “The ones we should be particularly concerned with are non-ionic detergents. Organo-silicon surfactants have proven to impact bees’ abilities to learn how to associate odors with nectar sources.”
Still another pesticide-related risk is related to pesticide seed-coatings. It seems they don’t always stick to the seeds where they are applied.
Corn seeds’ outer sheaths often prevent pesticide seed coatings from sticking to the seed’s surface. For this reason, chemical polymers called “stickers” must be applied to seeds to assure pesticides stay where they are applied all the way through the planting process.
Planters that use air to move seed from the planter boxes down through the seed injectors have proven to be capable of stripping seed coatings from kernels. Coatings then gather within dust clouds behind planters and will spread to nearby fields, where foraging bees will pick it up.
Some time ago, a concern was voiced that systemic pesticides might pass through plants to eventually reside in pollen or nectar and get picked up by bees. Research has shown that while pesticides do travel through plants this way, they arrive in flowers and blossoms in concentrations too low to be called a threat.
Noise over neonicotinoids
Last year, the European Union (EU) announced a two-year ban on a family of compounds called neonicotinoids. Less toxic than organophosphates or carbamates, they are currently the most widely used insecticides in the world.
Examples of products using them as active ingredients include Confidor, Admire, Gaucho and Advocate.
Neonics, as they are called, have also been identified as one of the two most serious pesticide threats to bees. The other consists of pyrethroid materials derived from chrysanthemums.
The EU ban specifically cites the risk of their use in the presence of bees and covers their use in proximity to bees and on vegetable crops. It went into effect this year and is being used as a means to gather data.
The threat is real, said Dennis vanEngelsdorp, a University of Maryland entomology researcher. “Neonicotinoids can cause colony-level mortality. It has also been found in waterways at high enough levels to kill insects.”
Mullin thinks the two-year ban may not provide enough data or show anything that is relevant. Similar to Reed, he has little faith in regulatory evaluation. Available testing regimens can only evaluate one chemical at a time.
“There are so many formulations of the pesticides,” he said.
Mullin also noted that there is recent research indicating there are also fungicides on the market that present serious risks to bees in sub-lethal doses.
When asked, the entomologists we interviewed for this story agreed the European ban resulted from how the EU deals with potential pesticide risks.
“In Europe, if a concern is raised over an herbicide or a pesticide, their regulators are more likely to ban it until it can be proven safe,” Johnson said.
In the United States, we do things differently. Johnson noted that after the Food and Drug Administration (FDA) registers a chemical, it is used until it is proven unsafe.
Mites and disease
The single greatest biological threat to the U.S. bee population is the varroa mite. A microscopic insect, it attaches itself to bees and drains their blood.
Bees typically pick them up when workers go out to forage. Having attached themselves to the workers, they are carried back to the hives where they attack other bees in the colony.
Another way they spread is during a kind of bee behavior called robbing. In September and October, the bee food is gone. In order to sustain themselves, stronger hives will range outward to locate and raid weaker hives for food.
“If the weaker hives were set back by varroa mites, the bees from the stronger hive, which may have fought off their own mites, are subject to attack again, but this time by stronger mites,” Mussen said.
Mites are starting to show resistance against nearly all of the miticides available. Amitraz remains the best defense against the varroa mite.
Similar to transport stress, varroa mites’ presence in bees makes them susceptible to outside pathogens. There are 22 named viruses known to affect bees and 16 of them are carried by the varroa mite, noted vanEngelsdorp.
“A half-dozen of them are outright killers,” Mussen said. “Normally, the bees can fight them off. But when stressed, the viruses become big problems.”
Like humans, bees can also be stricken by bacterial diseases. Chief among those are Nosema ceranae.
“You can knock it down, but when the protection wears off, it usually comes with twice the strength,” Mussen said.
American foulbrood is another bacterial infection. Beekeepers have been using antibiotics to control American foulbrood since the 1950s. The two antibiotics effective in the control of american foulbrood are terramycin and tylosin; when treated Foulbrood is resistant to terramycin, then tylosin is used to control it.
While there has been a lot of rhetoric from the federal government on how important honey bees are to the country, the monetary commitment to more research has been trivial. This year, USDA announced two research initiatives totaling $9 million.
Bees are responsible for the pollination of much of the nation’s commercial fruit orchards, almond plantations, to say nothing of cukes, squash and pumpkins. And yet the federal government’s commitment to finding new means to control mites and prevent viral and bacterial disease spread is less than $10 million.