This story was originally published by Reveal from The Center for Investigative Reporting.
For years, honeybees were dying, and no one knew why.
There have been some glimmers of hope recently. The number of bee deaths wasn't as dramatic last winter. Studies began pointing the finger at pesticides.
But a simple fact remains: Bees still are on the decline, and no one's sure why.
They're dying in large numbers, and scientists are scrambling to identify the cause. Beekeepers used to see about 5 or 10 percent of the bees in their hives die every year, but starting in 2006, losses jumped to 30 percent. About 10 million beehives, worth an estimated $2 billion, have been lost since then. The numbers are down slightly for last winter, when beekeepers lost about 23 percent.
A lot has changed since the issue exploded into public consciousness. Here's what you need to know about what could be causing the bee die-off and what can be done about it.
We need honeybees.
Bees are responsible for about one-third of the food we eat. They add $15 billion annually in value to American crops, according to the U.S. Department of Agriculture. And commercial agriculture depends on them.
Without honeybees, whole harvests of fruits, vegetables and nuts would fail. Alfalfa couldn't survive. That would lead to trouble in the beef and dairy industries, as well. Bees also pollinate oilseeds, which make up much of the world's supply of fat. Plus, cotton is an oilseed, which means the cotton trade would be in trouble, too.
A world without honeybees would look very different. See this slideshow.
Colony collapse disorder is the most famous phenomenon.
Colony collapse disorder leapt into headlines after a bad winter in 2006-07. It was dramatic, mysterious and unprecedented. Beekeepers and farmers sounded the alarm: The bees are disappearing.
With colony collapse disorder, the swarm vanishes without a trace. No dead bodies – just a lonely queen, her larvae and maybe a couple of nurse bees left caring for the larvae.
The disorder still occurs, and scientists still don't know what causes it. It is happening less, though.
Yet the bee population remains in decline.
It's not just colony collapse disorder that's destroying beehives.
Lately, beekeepers have been attributing more of their losses to problems with queen bees. They're not living as long, usually because they run out of sperm supplies too early. It's unclear why.
A queen mates once in her life. The sperm she gets should last her entire reign. When she runs low on sperm, the worker bees kill her, and a new queen takes the throne. In a healthy hive, this happens every few years.
Gene Brandi of the American Beekeeping Federation said that when he first started in the 1970s, he'd need about 500 new queen bees a year. Now, he's replacing as many as 1,500.
A shorter lifespan means the queen has less time to fertilize eggs. Therefore, there are fewer worker bees in the next generation to tend to the new round of larvae. And that means even fewer worker bees the following generation.
The higher queen turnover puts enormous stress on the hive. There might not be a new queen ready to replace her. Worker bees switch into overdrive as they race to raise a new queen – but it only works if larvae are younger than 3 days old.
If they're unable to raise a new queen, the hive is considered "hopelessly queenless." At that point, worker bees develop ovaries and lay eggs, but those eggs remain unfertilized. Unfertilized eggs can develop only into males. Once the all-male generation dies out, the hive is finished.
Why are the bees dying?
There's no one answer. But there are a lot of different theories. The answer likely is somewhere in these theories' overlap.
Theory 1: Parasites and pathogens
Many of the hives affected by colony collapse disorder were found to harbor varroa mites. These tiny parasites once were rare, but now they infest hives all over.
Varroa mites cause problems on two fronts. First, the mites suck fluids from the bees' bodies. That makes the bees weak and compromises their immune systems.
Second, the mite's bite leaves an open wound. That makes it easy for viruses to get in. The mites themselves pass along viruses that can lead to deformed wings and paralysis.
This combination of a compromised immune system and viral infection can team up to create a lethal effect.
But while varroa mites are found in many hives affected by colony collapse disorder, they're not always there.
Plus, the treatment for mites is a little like chemotherapy. It's hard on the bees, and the buildup of miticides could be part of the bigger problem. The chemicals can accumulate in beeswax, and that can lead to a weak queen or prevent a queen larva from developing, a 2006 study from the USDA's Bee Research Laboratory found.
Theory 2: Poor nutrition
Bees can survive a lot of stress, so long as they get enough good food.
But with more farmland being used to grow just one crop, bees aren't getting the mix of plants they need to eat well.
For example, bees pollinate watermelon crops, but watermelon pollen isn't particularly nutritious. Without time off to forage in other fields, they won't stay as healthy as bees that have access to a variety of pollens.
Even where there's uncultivated land, invasive plants that lack nutrition are edging out the wildflowers bees need.
In California, the drought also has had a major effect. Annual flowers aren't blooming, and perennials aren't producing nectar.
Plus, the honeybee isn't native to the United States. It's from Europe. As an invasive species, it's in constant competition with native pollinators such as bumblebees for the best flowers.
Theory 3: Pesticides
Scientists long have worried about pesticides' effects on bees.
But in the mid-2000s, major bee die-offs began making nationwide news. Around that time, beekeeper Brandi of the American Beekeeping Federation first noticed major losses among his and his colleagues' colonies. It also happened to be the 10th birthday of a new class of pesticides.
The use of neonicotinoids, or neonics for short, was exploding. In 1994, growers in California used about 5,000 pounds of neonics. In 2004, when Brandi's colonies first suffered major losses, growers in the state applied almost 129,000 pounds.
These new insecticides were celebrated for being less toxic to humans and birds, while being more toxic to insects.
Neonics are what's known as systemic pesticides. They aren't sprayed. Instead, the chemicals are applied to the seed itself, so as the plant grows, the pesticide is incorporated into the plant's tissue. When a bug takes a bite of a leaf, it ingests the neonic. Like nicotine, neonics are neurotoxic. They block a particular neurotransmitter, which allows a certain enzyme to build up. The insect's nerves overexcite. Paralysis and death follow.
Because the use of neonics was on the rise at the same time that bees began disappearing en masse, scientists wondered whether the chemicals could be the culprit.
Years later, there are a lot of studies that suggest that neonics are harming bees. For example, scientists increasingly are finding that it's the nonlethal doses that can wreak havoc, scrambling bees' sense of direction, making them more susceptible to disease or poor nutrition and causing bad reactions to cold weather.
But there are also studies that suggest that neonics are not harming bees. Researchers on these studies found that the level of neonic residue in pollen and nectar wasn't high enough to kill honeybees or harm them in the first place.
And plenty of others are inconclusive. For example, a report by the Xerces Society for Invertebrate Conservation found no link between neonics and colony collapse disorder. But it did draw attention to studies that found that neonics may have nonlethal effects on bees.
One analysis looked at 15 years' worth of previous neonic studies in 2012. It ended up calling for more research. It concludes that the existing body of evidence does show that neonics can harm bees in lab settings, but there's not enough evidence to prove those same effects happen in the field.
No study has taken the step of claiming neonics definitely cause colony collapse disorder. But there is growing evidence that at the very least, neonics play some role in the declining bee population.
Then there's the question of whether neonics do any good in the first place. Last year, Environmental Protection Agency researchers found that soy crops didn't benefit much from neonics.
Europe has banned some of the pesticides; the U.S. hasn't.
The European Union banned the three most common neonics at the end of 2013. The idea was to give researchers more time to study what effects these chemicals have on bee health. The EU will begin reviewing new neonic research in May.
In the United States, these three neonics, plus three others, still are used. The EPA plans to review the most common, imidacloprid, by 2017. It won't complete reviews on the other five until between 2017 and 2019.
The White House has convened a task force to make recommendations on how to better protect pollinators – not just honeybees, but also bats, birds, beetles, butterflies and other types of bees. The final report is expected by March.
Beekeepers and environmental groups are in the midst of a lawsuit against the EPA. They want the agency to suspend the use of clothianidin and thiamethoxam, two of the neonics now banned in Europe. These two pesticides were part of the EPA's conditional registration process, which speeds up the approval and registration of new pesticides.
A second legal action focuses on sulfoxaflor, a new type of neonic that the EPA approved in 2013. It is considered highly toxic to bees. The groups behind the action are requesting changes in the chemical's label and in the EPA's risk assessment process. They argue that the EPA didn't adequately address their concerns about the pesticide's effects on honeybee health before approving sulfoxaflor.
Europe is more cautious about the potential risks
The European Union banned neonics because of evidence that they pose a high risk to bees. The ban is in place until scientists determine whether they're the reason for the bee population decline.
The United States has not banned neonics because others argue that there isn't enough evidence that they harm bees. Regulators worry that banning neonics could cause economic problems without a guarantee it would solve the bee problem.
The Washington Post's Wonkblog has a good post breaking down the different approaches.
So what's the bottom line?
Bees still are dying in larger-than-average numbers in North America, Europe, parts of Asia and elsewhere. We're still not sure why. The debate over neonicotinoid pesticides, especially, continues to be heated.
But beekeepers and bee researchers generally agree that it's not just one thing killing the bees. In reality, some combination of the four P's is the culprit: parasites, pathogens, poor nutrition and pesticides.