Stinging the Bees

girl holds bee hive in front of cross

It's unseasonably warm for a February afternoon: The bees are sure to be flying. I gaze at the semi-circle of 14 crates, each like a stack of extra large shoe-boxes, as Jamie Fisher disappears into a tiny wooden shed, its red paint cracked and peeling. A moment later, she reemerges, her face hidden beneath a wide-brimmed hat covered with yellow netting. She hands me my own headgear, and I pull the mesh protection tight. A lone bee circles the hive, and my eyes dart anxiously, tracking his every move.

Fisher, a microbiology major with a passion for honeybees, ignites a small piece of wood and shoves it into a metal carafe. The bee lands on the handle, while a thin stream of smoke flows from the spout. "When a hive is disturbed, bees release alarm pheromones to warn other bees of the intruders," Fisher explains. "Smoke masks the pheromones and disguises our arrival—at least for a few minutes."

Fisher lifts off a super—the top layer of one of the crates—and quickly blows smoke into the hive. The colony is already alive. A bee buzzes around my head, zeroing in on my nose, poking against the netting over my face. I tense up despite Fisher's warning that bees sense fear. Trying to relax, I focus my attention on a bee resting on Fisher's thumb. She doesn't even notice it.

With her bare hands, Fisher brushes away about 50 insects, creating an opening in the comb. "Taste the honey," she invites. I hesitantly dip my finger and bring the honey to my lips. It is thick and warm from the sun. The sweetness lingers on my tongue.

In the fall of 1995, 11 wild colonies of Apis mellifera—honeybees—were located in the State College area. By spring, only two remained. Phone calls poured into Penn State's entomology department as beekeepers across Pennsylvania wondered where the bees had gone: Losses reached as high as 80 percent.

Surveys revealed a trend of failing queen bee health during the previous year, so with a sample of 325 queen bees, Scott Camazine, assistant professor of entomology, took on the task of scrutinizing every part of the queen, from thorax to ovaries. He and Fisher, along with others in his lab, discovered a possible culprit: microscopic mites in the queens' breathing tubes. These tracheal mites captured Fisher's attention.

The summer before her first year of college, Fisher already had more than 11 years of bee experience under her belt. She grew up with a 300-colony apiary in her backyard, the daughter of prominent beekeepers in the Stroudsburg area. Fisher first extracted honey from a hive at age seven and spent spring afternoons moving bees for pollination. (Honeybees are needed to pollinate many crops, from blueberries in Maine to oranges in Florida; they are more valuable for their pollination services than for the 209 million pounds of honey they produce annually.)

Fisher knew, for instance, that Mexican beekeepers had reported infestations of tracheal mites in the 1970s, and that by 1984, similar accounts had surfaced in Texas. Beekeepers had reacted with chemical insecticides, yet tracheal mites built up resistance, and fears of contaminated honey arose. Biological methods of control did not exist, because the microscopic mites live in the bees and separating mite and bee is nearly impossible.

In Camazine's lab, I gazed through the lens at the magnified honeybee trachea—delicate, diaphanous tubes joining together in the center of the bee's thorax. "In a healthy, mite-free trachea, like this one, the tubes are uniformly translucent," Fisher explained, as she poked at the trachea with a pin the length of a thumbnail. "In a mite-infested trachea, the two main branches would be clogged with mites."

Suddenly an eight-legged creature scuttled across my field of vision, and I jumped back from the microscope, startled. "Just a little varroa mite," Fisher said, laughing.

The reddish-brown varroa is about five times larger than the tracheal mite and is studied far more often. Female varroa lay their eggs in the cells of developing bees. After the bees hatch, they latch onto the spaces between the bee's body segments, feeding and passing along diseases. Entomologists have discovered more than 20 pathogens (seven of which are being studied at Penn State) that are transmitted by varroa mites.

Fisher plucked another honeybee from one of ten mini glass canisters lined up behind the microscope. With her fingers, she peeled away the cuticle from the exoskeleton of the thorax, revealing an infected trachea. The difference was astounding. The tissue had browned—a process known as melanization. Fisher delicately tugged on the trachea with a dissecting pin and pulled it from within the bee's thorax. She unzippered it to reveal hundreds of tiny mites.

"Their entire life cycle—from eggs to mature mites—occurs within the tracheal walls," Fisher said. They pierce the tracheal wall and feed on the hemolymph, or bee blood, living entirely within the bee's breathing tubes. Not only do they physically clog the tubes, the mites may also bring on an immune response, Fisher theorized.

The honeybee's exoskeleton is the first line of defense against foreign invaders, explained Diana Cox-Foster, the insect immunologist with whom Fisher worked on this part of her study. "Bees lack antibodies," Cox-Foster continued. "Instead they have blood cells, equivalent to human macrophages, which attack and ward off pathogens." Fisher and Cox-Foster looked at the bees' levels of glucose dehydrogenase (GLD)—enzymes active in insect immune responses. Where the trachea was ripped, GLD should be present.

But they found the opposite. Infected tracheae had less GLD than healthy ones. Something didn't add up, so Fisher and Cox-Foster decided to approach the problem from a different angle. "Ticks, distant cousins of mites, secrete substances that suppress the immune systems of their hosts," Cox-Foster said. It appeared that tracheal mites might also do so.

Mites peak in the winter and spring months. In cold weather, honeybees cluster together to stay warm, reproduction drops off, and their life span lengthens to three to four months—ample time for mites to enter a colony and infest it. When bees are buzzing in the summer, foraging for food, they live only three to four weeks—not enough time for mites to infest a colony.

This February afternoon is prime time for studying the honeybee-tracheal mite interaction. Fisher gathers a sample of bees from the apiary and totes them back to the lab in wire cages. She doesn't know which ones are infected, but some 30 percent of the colony has tracheal mites.

Fisher begins by anesthetizing the bees with carbon dioxide, not out of fear—Fisher has been stung hundreds of times—but because when honeybees sting, they lose their stingers and die. "Dead honeybees don't work in this study," jokes Fisher. With a micro-liter amount of bacteria on a tiny pin, Fisher stabs each bee in the muscle tissue of the thorax with one of three types of bacteria—Serratia, Pseudomonas, or Micrococcus. Then she waits, periodically monitoring the bees until their deaths, about 42 hours later.

If the immune systems of the mite-infested bees are compromised, sick bees should have more difficulty fighting off harmless bacteria. The results of this test are right on target. Serratia, a known pathogen, kills all of the bees quickly. Pseudomonas, fatal given the right conditions, kills some bees. Micrococcus, a nonpathogenic bacterium, does not kill healthy honeybees. Yet the mite-infested bees die.

"These mites are messing with the honeybee immune systems," says Fisher. "The bee's strength is zapped, and it's hard to fight off even small infections." Figuring out precisely how the mite does it ultimately will keep the bees alive.

Jamie Fisher is a microbiology major in the Eberly College of Science. Her adviser is Scott Camazine, Ph.D., assistant professor of entomology, 539 Agricultural Sciences and Industries Bldg., University Park, PA 16802; 814-863-1854; smc14@psu.edu. Diana Cox-Foster, Ph.D., is associate professor of entomology, 536 ASI Bldg.; 865-1022; dxc12@psu.edu. Their research is funded by the Pennsylvania Department of Agriculture. Writer Alison Balmat will graduate in May 2002 with a B.A. in French and geography, with honors in geography.

Last Updated September 01, 2000