A Canadian chemist who's also an amateur beekeeper recently grabbed international science news headlines as part of a team that unraveled the elusive chemical secrets governing life in the beehive.
For more than 40 years, scientists had been seeking the active ingredients of a pheromone produced in the queen honeybee's mandibular gland. One whiff of this pheromone compels worker bees to raise the queen's young and basically do her bidding, explains Keith Slessor, a chemistry professor at Simon Fraser University in Burnaby, British Columbia. By synthesizing the queen's hypnotic perfume, Slessor and his colleagues were able to answer questions about bee behavior that had stumped a long list of researchers stretching all the way back to Aristotle.
"I thought this was a neat thing to do and started keeping bees myself," Slessor says of his honeybee hobby, which he picked up from his father, who was also an amateur beekeeper.
Pheromones (from the Greek words pherein, meaning "to transfer," and hormon, meaning "to excite") are chemicals released into the environment by a variety of organisms--even you. Chemical codes in pheromones may help an organism attract a mate, compete more effectively for food, or protect life and limb from predators. Once they're out there, sex pheromones serve as signals to attract and sometimes alter behavior in members of the opposite sex. But don't get hormones confused with sex pheromones: Hormones are those rowdy internal secretions racing through your bloodstream. Pheromones, on the other hand, are your very own chemical calling card. Typically, pheromones are produced as liquids by specialized cells or glands. Then they're transmitted as liquids or gases.
Thus far, researchers like Slessor have analyzed pheromones from insects, algae, nematodes, spiders, crustaceans, fish, various cuddly mammals, and--you guessed it--humans. Read on to learn more about the chemistry of courtship and survival among bees, beetles, elephants ... and us.
"THE BEE GUYS": Chemist Keith Slessor (left) and biologist Mark Winston of Simon Fraser University won a BC Science & Engineering Gold Medal for their work on honeybee queen pheromones. JAMES LABONTE
Insects Win the Pheromone Prize
Because insects are so dependent on pheromones for survival, their chemical signals are especially fascinating to scientists who study animal communication. Over the years, pheromone chemists have picked up all sorts of interesting tidbits about insects. Female moths, for example, release a tiny bit of pheromone to call potential suitors. Flying males can detect the stuff from distances of several kilometers.
Meanwhile, back at the hive, pheromones released by the queen honeybee (Apis mellifera) stimulate worker bees to congregate, feed, and groom. Much of a queen's power over her subjects may be attributed to her primer pheromone, which primes worker bees to work. Wafting through the hive, this long-lasting pheromone "prevents worker bees from rearing a new queen," Slessor explains. It also forces them to lavish attention on the queen's offspring.
Scientists had previously identified compounds in the pheromone, according to Slessor. In fact, he says, beekeepers now use a synthetic spray version of the chemical, to help farmers enhance pollination and increase yields by attracting bees to blooming crops such as pears, kiwi fruit, and apples. But researchers didn't understand how queen bees make primer pheromone in the hive--until now. Turns out the queen makes primer pheromone in much the same way that worker bees crank out food for little larvae. (For details, check out Slessor's diagram of the two manufacturing processes.)
Life goes on, unless the colony gets too big. It's the job of messenger bees to pick up material from the queen and transport it to the rest of the colony. If the hive is crowded, Slessor says, those on the periphery may think the queen is missing, so they'll raise a new queen. He thinks this chain of events triggers swarming and the establishment of a new bee colony.
Beware of Beetles Bearing Gifts
In scientific literature, reports of female insects using chemical attractants are commonplace. But a study at the Cornell Institute for Research and Chemical Ecology recently revealed just how resourceful male insects can be when they're seeking a mate.
FOR YOU, MY DARLING: From a gland on his head, the male fire-colored beetle Neopyrochroa flabellata makes a chemical offering to a potential date. If she likes his chemical style, she'll like him, too. She'll also pass his sperm along to her offspring, to protect them from predators. TOM EISNER
As described in the June 25, 1996, issue of the Proceedings of the National Academy of Sciences, the male fire-colored beetle Neopyrochroa flabellata entices the female by presenting her with a chemical offering contained in a gland on his head. If the female likes the suitor's chemical style, she proceeds to mate with him. Since the male's sperm includes more of the chemical, the female passes it along to her eggs, thereby protecting them from predators.
According to Cornell University biologist Thomas Eisner, the chemical in question is none other than cantharidin, or "Spanish fly," the notorious "aphrodisiac" so graphically described in the last century (see sidebar).
"Isn't it ironic that a compound with a misplaced reputation in human sexual behavior is actually used for a sexual purpose by insects?" Eisner muses. In another interesting twist, it turns out that the fire-colored beetles don't produce the cantharidin themselves. Instead, they get it from blister beetles (probably by eating blister beetle eggs or dead beetles).
"It goes to show that we aren't the first to prospect for useful compounds (in nature)," Eisner says. "Here is a beetle that has become intimately involved in chemistry, and it pays off for him."
HE'S ONE HEADSTRONG DUDE: A scanning electronmicrograph of a male N. flabellata reveals the gland that contains chemicals for luring females. MARIA EISNER
Agricultural Fun With Pheromones
Since the 1960s, pheromone and pheromone-like substances (from plants that mimic pheromones) have come in handy for detecting and sometimes wiping out agricultural pests like moths and fruit flies.
California, home to 8 of the nation's top 10 agriculture-producing counties, grossed $22.1 billion in agricultural production in 1995 alone, according to the California Department of Food and Agriculture (CDFA). Since fruit flies can hatch, complete a larval stage, pupate, and start laying eggs in as little as two and a half weeks, they can devastate crops at an alarmingly rapid pace, resulting in heavy economic losses for farmers.
Fortunately, pheromones now help California researchers spot infestations at an early stage by luring unsuspecting male fruit flies to baited traps. By trapping a single male, the CDFA reports, authorities can respond quickly to control the infestation, applying the smallest possible amount of pesticides in exactly the right location. Without the pheromone detection system, the CDFA says, researchers would have to use many, many more pounds of pesticides.
Unfortunately, many destructive species of fruit flies can't be lured into traps because scientists still haven't figured out how to synthesize their specific pheromones. The field is, um, ripe for would-be pheromone chemists. "These are very interesting research topics, and we would love to have analogues or equivalent materials that are more volatile and more attractive to catch flies better," says Robert Dowell, an entomologist for the CDFA.
Chemists working with pheromone and pheromone-like materials can generally find job opportunities in government and university labs and in the private sector. "This is very applied research, all of which is funded by the agricultural industry," says Harry Shorey, a research entomologist with the University of CaliforniaRiverside. An expert on Lepidoptera (moths and butterflies), he has been working on pheromones since the 1960s.
"If the problem is Lepidoptera, then I come in and help," says Shorey, who knew early on that he wanted to devote his life to understanding insects. "As a kid growing up in Quincy, Massachusetts, I loved to lie on the ground and watch bugs crawl over me. I never grew out of it."
And You Thought Your Lab Was Funky
It never fails: Graduate students and postdocs always have to do the dirty work around the lab. Consider the case of chemist Terry Lee. He was a postdoctoral fellow at the Oregon Graduate Institute of Science and Technology in Portland when biologist L.E.L. ("Bets") Rasmussen asked him to help her analyze elephant urine--lots of it.
"Urine is a messy matrix containing thousands of components," Lee says diplomatically, when asked to describe his sinus-clearing search for elephant sex pheromone.
ELEPHANT EROTICA: Researchers sifted through 4000 liters of elephant urine to isolate this sex pheromone, known by the common name cis-7-dodecenyl acetate.
Several years and 4000 liters of urine later, Rasmussen, Lee, and their colleagues successfully isolated a pheromone released by female elephants just before ovulation. Apparently, Lee says, the pheromone lets bull elephants know that the time is right for romance. The work helps explain why a male elephant can always find his partner during mating season, even if he was separated from her for the rest of the year. Surprisingly, the elephant pheromone--commonly known as cis-7-dodecen-yl acetate--is the same compound used by various insects. (Of course, insects don't need as much pheromone as elephants do.) Practical applications for the research might include a technique for inseminating elephants in zoos, Rasmussen has reported.
Lee, now a research scientist at the City of Hope National Medical Center in Duarte, CA, credits a multidisciplinary approach with helping his team unlock some of the secrets of elephant reproductive behavior. "Biologists observe a phenomenon, but in order to really understand it, chemists bring it down to a molecular level," he says. (His findings, by the way, were reported in the Feb. 22, 1996, issue of Nature.)
Eau de Pheromone?
Compared with many other creatures, human guys and gals simply don't rely too heavily on their noses for sniffing out a Macarena partner. But new studies suggest that our sense of smell may be more important than was previously assumed. In fact, says Alan Hirsch, neurological director at the Smell & Taste Treatment Research Foundation in Chicago, people can lose sexual function if they lose their sense of smell.
Some researchers think olfactory research in animals may help explain human behaviors. Let's start with mice. Claus Wedekind, a zoologist at Bern University in Switzerland, says female mice sniff for mating partners with DNA that's different from their own, to help their offspring resist a wider range of diseases. Specifically, Wedekind says, female mice look for a mate with a different MHC (major histocompatibility complex), a protein complex that lets the immune system know when disease is present, spurring killer T cells into action. Similarly, researchers say, human females are more likely to be turned on by a guy's body odor if he has different MHC.
Even if a gal turns up her nose at first, researchers have learned, a relationship may flower later, when her body is more receptive. In studies at the Ludwig-Bolzman-Institut in Vienna, 290 young women who were ordinarily turned off by androsterone (a key component in a guy's sweat) were less grossed out by it while they were ovulating. Androsterone, it seems, may act as a pheromone that sorts women, increasing the likelihood of fertilization by making even smelly guys seem more appealing. In a companion study, 66 nonsmoking guys were asked to sniff water or copulines (that's right--components of female vaginal secretions). Next, researchers asked the guys to check out photographs of women and rate their attractiveness. Because the scent of a woman made guys give women higher marks, researchers say copulines may help level the reproduction playing field, allowing all women to compete in the reproductive game.
Fragrance makers have been adding animal pheromones to their products for centuries. Alas, animal pheromones may work better for pigs and deer than for humans. In 1993, however, the Erox Corp. in Northern California started selling fragrances based on synthetic versions of human pheromones, isolated from skin tissue by researcher David Berliner, now chief executive officer of Pherin Corp. in Menlo Park, CA. After sniffing Erox fragrances, sold under the Realmª product name, company literature says, women feel warm and sensual, while men supposedly gain confidence. The company is careful to steer clear of aphrodisiac claims, but it points out that the vomeronasal organ (VNO), a tiny cone-shaped receptor inside the nasal passages of most mammals, may be a pheromone receptor in humans. Because the human VNO wasn't thought to respond to odors, researchers had long described it as a nonfunctional artifact of evolution. But new studies, primarily by Berliner and crew, suggest that pheromones cause the VNO to trigger nerve impulses linked to the hypothalamus--the part of the brain that controls your fight-or-flight response, hunger ... and yes, your sex drive.
Swatting Spanish Fly Claims
Cantharidin or Spanish fly gained notoriety as an aphrodisiac in the last century, when a French Foreign Legion doctor reported examining soldiers with painful, prolonged erections, says Thomas Eisner,
a biologist at Cornell University.The soldiers' discomfort, Eisner explains, was attributed to eating the legs of frogs known to feed on blister beetles, which produce cantharidin. (Common names for blister beetles include cantharides or Spanish flies.)
Cantharidin (hexahydro-3,7-dimethyl-4,4-epoxyisobenzofuran-1,3-dione) will most definitely irritate your genitourinary tract and dilate your associated blood vessels, causing real (and very painful) physical symptoms. So it does, like any poison, give you the hots, but researchers say its aphrodisiac effects have never been substantiated. In people, the toxic dose is a mere one-tenth of an ounce, and 32 mg is likely to kill you, according to Peter
V. Taberner, who wrote Aphrodisiacs: The Science and the Myth (University of Pennsylvania Press: Philadelphia, 1985).But fire-colored beetles seem to like cantharidin. Eisner's research show that male beetles use cantharidin as a sex pheromone.