Dark Banquet (27 page)

According to Gwilym O. Evans, author of
Principles of Acarology,
acarines are unlike other arachnids because of the intimate associations they've developed with other animals. In mites, these associations range from symbiosis to commensalism to parasitism.

Briefly, symbiotic relationships are those between two different organisms in which both derive some benefit. Among the acarids, perhaps the strangest example of symbiosis is the relationship between the eastern subterranean termite
Reticulitermes flavipes
and the slime mite
Histiostoma.
Researchers have found that termite colonies often become infected with a pathogenic fungus
(Metarhizium anisopliae).
The fungus invades the termite's body, secretes a fatal toxin, and then derives nutrients from the decomposing wood muncher. Finally, the rootlike fungal mycelia erupt through the cadaver's exoskeleton to grow and spread reproductive spores throughout the termite colony. So destructive is this fungus that it's even been considered for use in the biological control of termites. Fortunately for the termite (although unfortunately for homeowners and pest-control types), the slime mites living in the nest not only scarf down the pathogenic fungus, but as they cruise around the nest they spread a trail of bacteria, yeast, and other microbial organisms. This sets up competition between the pathogenic fungus and these nonlethal decomposers with the result being the suppression of growth and sporulation (release of the reproductive spores) in
Metarhizium.
In many ways, it's as if the slime mite is able to serve as an external immune system for the termite.

Commensalism (another type of mite/animal association) is a relationship between two organisms in which one benefits and the other neither benefits from the relationship nor is harmed. One example, in the case of mites, is a form of commensalism known as phoresy, in which a smaller organism (in this case, the mite) attaches itself to other organisms (like an insect) for the purpose of transportation. Since the carrier isn't harmed, you can think of phoresy as a milder version of the passive transport we saw in bed bugs. In perhaps the strangest case of phoresy, hummingbird-flower mites
(Proctolaelaps kirmsei)
are chauffeured from flower to flower within the nasal cavities of the hummingbirds. Although the hummingbirds aren't physically harmed by the mites, they both wind up competing for the same pollen and nectar—and so this isn't really a textbook example of commensalism.

Acarologist Tyler Woolley lists five significant ways that mites affect humans:
health
(through transmission of diseases as well as our bodies' allergic and inflammatory reactions to them),
agriculture
(they infest crops, household and garden plants, and farm animals),
stored agricultural products
(they cause tremendous damage to grains, cereals, and veggies in which they live and multiply),
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biological control
(in which predatory mites are involved in controlling pests like fire ants or even other mites), and
aesthetics
(nobody likes a mangy mutt or mite-damaged houseplants).

As a group, mites exhibit a bewildering variety of ways to make a living. For example, approximately 140 species of them have been identified as living in house dust. Additionally, if you look closely enough you'll find mites infesting algae, books, cheese, dried fruits, dried meats, drugs, flour, fungi, furniture, grains (like corn, wheat, oats, barley, rye, buckwheat, and millet), jams, jellies, mattresses, mildew, mushrooms, nectar, nuts, paper, plant bulbs, pollen, seaweed, seeds, spores, straw, sugar, vanilla pods, and wallpaper. Mites affect hundreds of plant species, and pretty much every type of wild animal, farm animal, and pet you can name. For creatures troubled by mites, infestation sites range from ears to anuses and all stops in between.

Besides an allergic reaction to dust mites and their droppings, perhaps the most commonly encountered mite-related health problem is scabies. Caused by
Sarcoptes scabiei.
Scabies is a condition that produces a rash and intense itching.
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The symptoms result from the host body's reaction to mite-secreted and-excreted substances released as the mites go about their parasitic business. Young female scabies mites, which are about one-fiftieth of an inch long (a half millimeter), excavate a burrow in the host's skin where a male soon joins them. Copulation occurs only once and renders the female fertile for life. Soon after, she emerges from the honeymoon suite (leaving the male behind to die). The pregnant female motors around the surface of the host (reaching speeds of up to 60 inches per hour) until she locates a site for a permanent burrow (hands and wrists are popular). Burrowing at a rate of about one-fifth of an inch per day (five millimeters), the female feeds on liquid from ruptured host cells. She also takes time to pump out several eggs per day, which are applied to the walls of the ever-lengthening burrow. When the larvae hatch, they leave mom and their nursery burrow behind, passing through several instars before reaching adulthood. During their wanderings topside, scabies mites are commonly spread to new hosts during periods of prolonged physical contact.

Until relatively recently, scabies was thought to be a disease of the poor, the unwashed, and the sexually promiscuous. This view was challenged in a rather unique manner in an article titled “Scabies Among the Well-to-Do,” published in 1936 in the prestigious
Journal of the American Medical Association:

Scabies is a disease of herding, promiscuity and travel, of family school and vacation life. A plague of armies, tenements and slums. It may with equal force invade a pedigreed school, Camp Wawa Wawa or the baronial castle on the hill. An ever present differential consideration, wholly without social boundaries, the possible explanation of the itches of the tycoon, the socialite and the university professor equally with the mechanic's daughter on relief.

Another mite causing
major
concern today is
Varroa destructor,
which preys on several types of bees, including honey bees
(Apis)
and bumble bees
(Bombus). Varroa
can be considered an invertebrate vampire because it feeds on hemolymph. Since the bee's circulatory system doesn't function in gas transport, there is no oxygen-carrying hemoglobin, and as a result hemolymph lacks the red color of vertebrate blood. It is, however, a complex liquid containing a variety of hemocytes, cells that carry out many of the same functions as their leukocyte counterparts—functions that include phagocytosis and a role in the immune response. There's even a hemocytic version of stem cells.

Female mites enter bee nests (or hives) where they lay their eggs just before the brood chambers containing the developing bees are capped by the adult bees. The parasites feed on larval and pupal instars as well as the emerging adult bees, which are also used for transportation. As with other arthropod parasites, as
Varroa destructor
feeds it can transmit viral and bacterial pathogens to its host.

Recently, the dramatic and nearly worldwide loss of honey bees has become a major concern not only within the beekeeping industry but also among farmers who raise the more than ninety commercial crops commonly pollinated by bees.
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Colony collapse disorder (CCD, formerly known as fall dwindle disease) is characterized by the sudden departure of most of the adult worker bees from the hive, leaving behind the queen, a few young workers, and an abandoned brood of larvae and pupae. Although the cause of CCD is still under investigation, the list of potential suspects includes mites, bacteria, fungi, viruses, long-term exposure to substances like pesticides—especially neonicotinoids (chemicals that mimic the neurotoxic effects of the compound found in tobacco), and poor nutrition.
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There is even a suggestion, albeit far-fetched, that cell phones are the causative agent.

In a pilot study published by the International Association of Agriculture Students, researchers at the University of Koblenz/Landau in Germany, placed cell phone handsets near four of eight beehives. They set out to measure hive-building behavior (by comparing before and after photographs of the hive chambers) as well as the tendency of the bees to return to their hives after they'd been captured, marked, and released some eight hundred meters away. Although the researchers reported that during the experiment “it became clear that both weight and area (of the hive) were developed better by non-exposed bees” statistical analysis “never showed a difference between exposed and non-exposed colonies.” Oddly, in their Results section, the authors presented only
half
of their bee return data. They reported that in one exposed colony, only six of twenty-five test bees returned home within forty-five minutes, while in a second exposed colony, no bees returned. These incomplete findings triggered the publication of several articles (e.g., “Scientists Claim Radiation from Handsets Are to Blame for Mysterious ‘Colony Collapse' of Bees,” “Cell Phone Plague Obliterates Bee Colony,” “Honey Bees Can't Call Home”) purporting to inform readers of the dramatic new scientific developments. Typical was an editorial in the
Waco Tribune Herald
(April 16, 2007) in which the author stated that “a growing theory is that cell phones cause bees to become so disoriented that they cannot find their way back home.”

The original researchers were clearly not amused. According to Dr. Wolfgang Harst, the lead author, “This evolved as a case study for us in the new ‘copy and paste' journalism.” Harst slammed “the erroneous depiction of our study,” from “faulty facts” about the study itself, to the claim that “handsets are to blame for ‘colony collapse.'” He informed me that the follow-up study is set for publication in the journal
Environmental Systems Research
and that “although the findings are not so ‘alarming' or ‘breathtaking' as in 2005, the differences we found between the full irradiated and non-exposed bees were significant.”

A number of researchers have published studies strongly suggesting that CCD is caused instead by a virus transmitted to bees (and/or activated) by
Varroa destructor,
the previously mentioned, hemolymph-sucking bee parasite.

Two closely related viruses have been implicated: Kashmir bee virus and Israeli acute paralysis virus.
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These viruses are thought to be common infective agents within bee colonies (approximately eighteen bee viruses have been described) until stress or another problem (like
Varroa
) causes them to become epidemic and lethal.

“They've been selectively breeding different honey bee strains for years—for traits like mild temper, honey production, and resistance to mites,” said Kim Grant, biologist and beekeeper. “It's certainly possible they've also bred in some things they
hadn't
planned on—like susceptibility to some of these bee viruses or compromised immune systems.”

Currently, scientists are trying to determine methods to stop the spread of CCD—many of which involve
Varroa.
These include the development of new miticides and the introduction of
Varroa-
resistant bees into European and American bee colonies. Clearly, though, beekeepers and farmers are taking CCD extremely seriously since the potential exists for a global nightmare should the world's bee populations disappear.

Scientist and
New York Times
best-selling author Dr. Charles Pellegrino, a polymath whose novel
Dust
took an apocalyptic view of what would happen should the earth's insects go extinct, was less than optimistic about the ramifications of a honey bee extinction event.

“So what do you think is causing this?” I asked him in the spring of 2007, as we sat on my favorite bench in Washington Square Park.

“The feeling from people I've talked to with the CDC is that weakened bee immune systems seem to be the issue here, with mite infestations more of a secondary symptom.”

“What's compromising their immune systems—cell phones?”

There was a pause and Dr. Pellegrino frowned. “You're kidding me, right?”

I shrugged.

“Well, it's still a bit of a poser,” he continued. “If it's a viral agent like they're saying—even something akin to ‘bee AIDS'—then I'm not terribly worried. Viruses usually adapt very quickly to their hosts—and a bad parasite usually ends up dead, inside its dead host. A viral problem can be expected to quickly self-correct.”

“You mean evolve into a nonlethal strain?”

“Right. But if it's a fungus weakening their immune systems, that could be much more problematic.”

“Why's that?”

“Fungi adapt more slowly than viruses or bacteria. Plus they're resistant to all but the sorts of antimicrobial agents that would kill the bees as well as their parasites.”

I figured it was time to bring out the big guns. “What would happen if all the bees went extinct because of CCD?”