Diseases and Parasites Come to the Americas
- Part 3

Karen Edmundson Bean is a nationally published freelance journalist specializing in science and the environment. She is also an award-winning producer/writer/cinematographer of natural history and backcountry videos (www.Walking-Wild.com) and one of the few women to hold director of photography status in the International Cinematographers Guild. Her farm in Maple Falls is home to her cashmere goats, Shetland sheep and, of course, honeybees.

Part 3

“Technology … is a queer thing. It brings you great gifts with one hand, and it stabs you in the back with the other.” — C.P. Snow

The last 60 years have presented honeybees and native pollinators with a number of formidable challenges. In that time, nearly 60 percent of managed honeybee colonies vanished in the United States, and feral honeybee colonies were nearly wiped out. Native pollinators suffered an equally heavy blow in the United States and throughout the world.

In Great Britain and the Netherlands, native bees have suffered an 80 percent decline in areas examined in a recent study. Pesticides and the loss of habitat, including the rise of monocultures, are responsible for some of these losses. These factors were addressed in Part 2.

Technology keeps delivering both benefits and blows to pollinators. The modern age has brought the world closer together with high-speed travel and international trade. It also brought new diseases and parasites that found hosts in the bees established in the western hemisphere. Some of these deadly invaders have devastated honeybee colonies; one of them has caused the virtual disappearance of at least one native bee in the United States.

Bumblebees are bred for use with greenhouse tomatoes. An error in breeding may have nearly wiped out one species, Bombus occidentalis. Some of these bumblebees were sent from the United States to an established European breeder with markets in Europe and North America. When their decedents returned to the United States, they carried a virus for which our native bumblebees have no resistance. Had the imported bees remained inside of their greenhouses, as required by law, there might have been no effect. But bumblebees are small and fast.

Some of the European-bred bees escaped and carried their new virus to their wild relatives. Today, Bombus occidentalis, which was once common from California to British Colombia, has all but vanished. “It has become rare, not extinct, but hard to find,” explains Mace Vaughan of the Xerces Society for Invertebrate Conservation. “This year an expert found one bee in the Willamette Valley [Oregon]. In Utah one worker bee was found, and a handful are still hanging on in the Rocky Mountains.”

Bombus occidentalis has been designated a very endangered species by the Xerces Society. Five other bumblebees also carry this designation; imported diseases threaten all of them. The Franklin bumblebee, Bombus franklini, is considered critically endangered by the Xerces Society, and is considered a “Species of Concern” or a “Special Status Species” by the U.S. Fish and Wildlife, the Bureau of Land Management, as well as the Oregon and California Departments of Fish and Game. The Franklin bumblebee flies in a small area of the Siskiyou mountain range in California and Oregon. Imported diseases are among the threats that hang over this unique bumblebee.

Diseases caused by bacteria, fungus and microbes have long been a hazard to honeybees and a bane to beekeepers throughout the world. One fungal disease, chalkbrood, a larvae killer, was documented for the first time in Germany in 1911. It quickly spread throughout Europe. In 1972 chalkbrood hit honeybees in California. It soon spread throughout the United States. Its arrival here is suspected to have been in a shipment of pollen that was imported from Europe in the 1960s.

Larger threats to honeybees travel on a free ride into the United States. In 1998 an arrival from South Africa, the small hive beetle, began to wreak havoc among hives in Florida. These recent imports tunnel through honeycomb, destroying the bees’ stores of honey and pollen. If the infestation becomes severe, the bees will abandon their hive. Beekeepers are continuing to explore ways of defeating this pest, but none have proved completely effective. While the battle continues, the hive beetle travels along with bees used in pollination throughout the South and is now entering the Midwest. The small hive beetle is just the latest in a line of imported pests who threaten honeybees’ survival.

The tracheal mite, the first parasitic import, arrived in Florida and Texas the early 1980s. These tiny mites infest the breathing tubes of honeybees. They spread throughout the hive, and suffocate the bees one by one until the hive dies. In 1904 they nearly devastated honeybees on the Isle of Wight, and in 1921 they were found in Great Britain where they nearly decimated all honeybees before they spread to Europe.

The massive die-off of infested bees prompted the United States Congress to pass the Honey Bee Act in 1922, which restricted the importation of honeybees. The mites never heard about the law. It’s believed they flew across the border in Texas, and arrived with a shipment of bees in Florida. When they finally made an appearance, they made their presence well known. In Florida, they caused the destruction of nearly all the hives in the area where they were first discovered.

The tracheal mites soon spread throughout the United States. Honeybees throughout the world have survived this infestation by adaptation through natural selection. Those bees who had a resistance to the mites survived and continued to breed. It’s been discovered that the longer the mites are in an area, their effect on hives has less impact, although that impact can still be deadly.

“Bees have the ability to deal with tracheal mites. There is evidence for that in Europe, where all the susceptible colonies were eliminated [by the mites]. I think the same thing will happen here,” explains Dr. Steve Sheppard, who holds the Thurber Chair of Apiculture, Department of Entomology, Washington State University in Pullman.

In the meantime, many researchers continue to look for a way to deal with tracheal mites. Sheppard helped to get mint oil, the same component in cough drops, registered as a treatment in Washington state. His studies later found that it only aided one out of eight colonies. In 1999 Sheppard and his students stopped all treatment and began to select for resistance to tracheal mites through natural selection.

A far more deadly foe of honeybees arrived in the late 1980s: the varroa mite (see Part 2). These mites, who have a scientific designation any thriller movie would be proud of — Varroa destructor — live up to their name. In the last 15 years, millions of honeybees have died. Tens of thousands of hives were lost, which drove many commercial beekeepers out of business. This mite is the vampire of the bees’ world. It feeds on hemolymph, the equivalent of blood in bees.

Varroa mites chow down on both adult bees and larva. They ride on the bees and spread through contact. When infested bees visit other hives or swarm to new nesting areas, the mites go with them and discover new hosts.

Beekeepers may inadvertently spread mites when they manipulate frames of bees and brood (young larvae) between hives during the course of their work. The mites may also hitch rides on queen bees and packages of bees that are shipped from one area of the country to another.

How the varroa mite arrived in the United States is still unclear, but they were first identified in Wisconsin in 1987. It’s assumed that, by this time, they were already well established in the United States. Their unrelenting spread had been watched for years with dread by beekeepers.

Varroa mites hail from Asia where they prey on Apis indica, a bee that has long adapted to their presence. Over a century ago, settlers in Asiatic, southeast Russia introduced a new bee to the area, the western honeybee, Apis mellifera. This is the same species of bee that was imported to North America. The varroa mites found these bees as tasty as their original hosts, and spread throughout the hives.

With the arrival of modern transportation, they spread throughout the world. In the 1950s varroa mites moved through Asia, Russia and the Middle East, and kept on going: 1960 to Bulgaria, 1971 to Paraguay, 1975 to Tunisia, 1987 to Wisconsin. Today they are on every continent in the world, except Australia.

Initial treatments for varroa mites in the United States have been pesticides, which are placed in the hives to kill the mites. One of these chemical treatments uses the insecticide coumaphos as its active ingredient. Coumaphos is approved for use on varroa, but banned for most other purposes in the United States. This organophosphate was developed for chemical warfare during World War II.

Organophosphate insecticides, when used on crops, were responsible for the death of 43 percent of the honeybees in the United States after World War II, according Dr. Nan Vance, research plant physiologist at the Pacific Northwest Research Station of the National Forest Service. The treatment is intended for use only after all honey for human consumption has been removed from the hive.

The placement of an organophosphate in a hive comes with side effects. Studies have shown that queen bees in hives where coumaphos is used have lower weights, shorter lives and are often rejected by the hives. Many commercial beekeepers feel that this is a small price to pay for keeping their hives alive.

“People with 10 colonies may get by without chemical treatments, but commercial beekeepers can’t,” Sheppard explains. “So miticides are used in colonies. We can’t let the 2.3 million remaining colonies die. Commercial beekeepers will say that without pesticides, they will be out of business.”

Varroa has hit hard, Sheppard points out. Today good beekeepers may face a loss of 20 to 50 percent of their hives in a year, a loss Sheppard cites as being primarily caused by varroa mites.

The dependence on pesticides to fight varroa is due in part to the shift in demographics of beekeeping as people moved from small farms to the cities. Miticides could be abandoned “… if we had 100,000 people with 20 hives, but we have a few people with 5,000, 10,000 or 20,000 hives. Their bees are handled like an industry,” he explains.

Coumaphos is the third miticide to be used on honeybees. There is a fourth in the works. New miticides need to be constantly invented because mites quickly develop resistance to the pesticides. This resistance is often aided by the actions of the very people who are fighting the parasites. “Beekeepers dream up their own treatment, using the active ingredients in the miticides,” sighs Sheppard.

Fulvalinate, used in the second miticide developed, has an active ingredient present in cattle dip. Some beekeepers soaked tongue depressors in the dip and placed it in hives. This reduced the beekeepers costs. It also helped varroa mites in many areas to develop a resistance to the insecticide. Fulvalinate is traditionally used against moths, beetles and bugs, like aphids and cicadas that pierce and suck their prey.

The first miticide developed was pulled from the market by the manufacturer, following a lawsuit filed by beekeepers when the pesticide failed to protect all their bees. The fourth miticide is expected to be available in one to two years. Researchers believe it, like the others, will be viable for four to five years; then the mites will, once again, become resistant to the pesticide.

Alternative treatments are constantly being developed to control varroa mites. The substances are as varied as their proponents. They include powered sugar, the essential oil thymol, mineral oil, formic acid, oxalic acid, sugar esters, fungus and tiny predators; the list is extensive. Sheppard points out that most of these treatments are not as affective as miticides, and others are too time-intensive for commercial beekeepers with tens of thousands of hives.

Varroa mites changed beekeeping in many ways, including the physical construction of hives. Before varroa, all beehives traditionally had solid floors. It was found that when bees picked the varroa mites off each other, they would toss them down to the hive floor. The mites would simply walk back up and climb onto a passing bee. This inspired some beekeepers to integrate a screened floor above the bottom of their hives. When the mites fall through the screen, they have a much more difficult time climbing back into the main body of the hive.

Throughout the disaster, bee breeders have continued to work toward bee stock that is mite tolerant. “The real arena is in genetics and the breeding of bees,” Sheppard says. “We will never eliminate the mites … . Bee breeders need to select for a bee more tolerant to mites. That hasn’t been done by commercial queen producers in the past … . They are now realizing that they need to bring selection pressure from mites into breeding programs.”

Some bee breeders and beekeepers now introduce mite tolerant bees to their bee yards. Sheppard’s programs at Washington State University “have a breeding program for bees that are tolerant to mites.” He says, “In 2005 we didn’t treat at all for mites.”

At the University of Minnesota, entomologist Marla Spivak breeds bees with the ability to protect themselves through good housekeeping. They’re called the Minnesota hygienic bees. Varroa mites breed on bees’ larvae. When Minnesota hygienic bees sense the presence of mites on larvae, or larvae that is ill, they remove the mites and/or larvae from the hive.

Sue Cobey used Carniolan bees, Apis carnica, to develop New World Carniolans in 1982 in California. In 1990 the breeding project relocated to Ohio State University. These bees are also being selected for resistance to tracheal mites and for hygienic traits that will encourage tolerance to varroa mites.

In 1997, the United States Department of Agriculture added a Russian race of Western honeybee too the mix. These imported queens were descendants of Western honeybees which had lived for over 150 years in southeast Russia alongside both varroa and tracheal mites. Through years of natural selection, the bees had built up a degree of tolerance to mites. These Russians were the decedents of the first Western honeybees to encounter varroa mites; they were the bees that traveled with settlers to eastern Russia. Russians, New World Carniolans and the Minnesota hygienic bees are part of the effort to establish a substantial population of mite tolerant bees.

“We will have varroa tolerance within the next 10 years,” Sheppard exclaims. “We need to because mites have such a short lifespan compared to bees, so they will continue to become resistant to miticides.” Then the challenge will be to incorporate the new stock into bee breeding programs.

Sheppard looks to smaller bee breeders and queen producers to spearhead the move toward the use of genetically tolerant stock. “As work here at WSU and at the other breeding programs shows some success, the big guys will catch on.” The large breeders have a system in place and “they want to see results before they switch.”

Those results are beginning to appear as researchers and bee breeders work toward bees tolerant to Varroa destructor. Nature, and the miracles of modern transportation, however, have more challenges in store for honeybees. “There are some other nasty mites on the horizon” according to Sheppard. Varroa jacobsoni, another varroa mite, has the potential of reaching the United States. Varroa destructor was at first mistaken for this mite.

Southeast Asian bee mites Tropilaelaps spp. (T. clareae and T. koenigerum) have already been found on colonies of the Western honeybee in Thailand. “They are much more damaging than varroa,” says Sheppard. These mites are an active group of parasites. They run about the hive, feeding on bee larvae and pupae. The result is deformed brood and dead bees. The hive will ultimately die, or the survivors will leave to form a colony away from the infected hive. Northern beekeepers may be spared this onslaught because Tropilaelaps mites need brood (young larvae) to survive. Bees in northern regions have no brood during winter months.

Southern and migratory beekeepers, whose bees never experience a true winter, are watching the movements of this new mite with dread. “There’s nothing much we can do about them right now,” Sheppard admits. “It’s wait and see.”

New parasites and diseases that attack honeybees and native pollinators will probably always be on the horizon. The speed at which they now travel around the world is a hazard of the modern technology that surrounds us. That same technology can help bring genetic solutions to aid honeybees’ survival and progress to the research needed to halt the decline of native pollinators. Hope still exists for native and nonnative pollinators, but it will take the efforts of all concerned people. The next series in this article will look at what we all can do to help ensure the survival of pollinators. §

Next Month: The Future of Pollinators