The Lives of Bees

by Thomas D Seeley

  to water sources, so they can meet their water needs without maintaining

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  large water reserves in their nests. Reliance on external water sources,

  however, requires activation and deactivation of a colony’s water collectors

  as conditions change. Recently, Madeleine M. Ostwald, a Cornell under-

  graduate student, worked with me and one of my PhD students, Michael

  L. Smith, to investigate how a colony’s water collectors are activated and

  deactivated. To do so, we moved a colony living in a glass- walled observa-

  tion hive into a greenhouse, where we could control the bees’ access to

  water. We provided the bees with just one water source, which was set on

  scales; by measuring its drop in weight, we could measure precisely the

  colony’s water collection during our experiments. We then stimulated the

  colony’s water collection by heating the observation hive with an incan-

  descent lamp, and when bees began visiting the water source, we labeled

  these water- collector bees for individual identification. By closely watch-

  ing the behavior of the water collectors inside the hive on days when we

  again gave the colony a heat stress, we saw how the colony’s water collec-

  tors sprang into action (Fig. 9.10). These bees did so about one hour after

  the heat stress began, which showed that the water collectors were not

  responding to the high temperatures in their nest. Instead, these bees were

  stimulated to resume their work by experiencing either greater personal

  thirst or more frequent beggings for water, or both. A previous study, by

  Susanne Kühnholz and myself, found that once a water collector has sprung

  into action, she keeps informed about her colony’s water need by paying

  attention to what she experiences when she returns to the hive and seeks

  to unload her water to other bees (water spreaders). The higher the colo-

  ny’s water need, the fewer unloading rejections she experiences and the

  faster she delivers her water load.

  Fig. 9.10. Changes in behavior of water collectors in a colony when it experienced

  brood- nest overheating and was temporarily deprived of water collection.

  Experimental treatment: brood nest was not heated for first hour, then was

  heated and water was withheld for two hours, and finally water was provided ad

  libitum outside the hive. Six focal water collectors were observed repeatedly over

  the five hours, to determine the proportion of time these bees spent standing,

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  Broodnest

  ) 40

  Ambient

  30

  Temperature (˚C 20

  d 0.8

  Standing

  Walking

  Begged

  0.4

  Proportion of observation perio 0

  20

  10

  Number of collectors visiting water source 0

  ) 8

  4

  Water collected (g 0 9

  10

  11

  12

  13

  14

  Time of day (h)

  walking, or being begged for water. A roll call was made every 15 minutes of the

  water collectors (labeled with paint marks for individual ID) that visited the

  water source. Amount of water collected was measured by weighing the water

  source every 15 minutes.

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  While it is true that honey bee colonies do not maintain large water

  stores in their nests, beekeepers have reported finding some water

  (amounts not specified) stored in the combs of colonies during droughts

  in Australia and South Africa. A second means of water storage is for

  worker bees to hold water in their crops (honey stomachs). O. Wallace

  Park reported finding clusters of reservoir bees—workers with swollen

  crops containing dilute nectar—in a colony in Iowa in early spring, when

  the weather was chilly and the bees were rarely able to obtain water for

  rearing brood. He also observed water collectors flying out en masse from

  a colony living in an observation hive. These bees gathered water from

  grass blades and puddles, and upon return to the hive they transferred

  their loads to other bees that served as the water reservoirs. Madeleine M.

  Ostwald, Michael L. Smith, and I also found water- filled bees standing

  quietly on the combs in our observation hive in the evening after the study

  colony had experienced a day of heat stress combined with water depriva-

  tion. Moreover, we found water stored in the comb cells located just inside

  the hive entrance. It now seems clear that temporary water storage in

  reservoir bees, and in comb cells, is an important part of the social physi-

  ology of honey bee colonies.

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  10

  COLONY DEFENSE

  Life consists with wildness.

  The most alive is the wildest.

  —Henry David Thoreau, “Walking,” 1862

  Every living system faces a legion of predators, parasites, and pathogens,

  each of which is equipped with a sophisticated tool kit for penetrating the

  defenses of its prey or host. In the case of a honey bee colony, there are

  several hundred species, ranging from viruses to black bears, whose mem-

  bers are forever trying to breach the bees’ defenses. What makes a bee

  colony so attractive to so many is, of course, the store of delicious honey

  and the horde of nutritious brood that lies inside its nest. In summer, the

  combs inside a bee hive or a bee tree typically hold 10 or more kilograms

  (20- plus pounds) of honey, plus thousands of immature bees (eggs, larvae,

  and pupae). Moreover, these brood items are neatly packed together in the

  warm center of the bees’ nest, making them an absolute bonanza for any

  viruses, bacteria, protozoa, fungi, and mites that succeed in infecting or

  infesting this host of developing bees. Clearly, a colony of honey bees is an

  immensely desirable target. It is also a perfectly stationary target. Because

  a colony’s beeswax combs are a huge energetic investment, and because

  these combs are often filled with brood and food, a honey bee colony can-

  not afford to find safety by fleeing its home when threatened. Instead, it

  must cope with its foes by standing its ground, and usually it succeeds, by

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  drawing on a sophisticated arsenal of biochemical, morphological, and

  behavioral weapons.

  Given that honey bees have a 30- million- year history, it is likely that

  most of the relationships between Apis mellifera and its predators and agents

  of disease are long- established. We can expect, therefore, that colonies

  living undisturbed in the wild possess defense mechanisms that usually

  prevent pathogens and parasites from multiplying sufficiently to cause se-

  vere disease. Indeed, it is likely that wild colonies of honey bees have

  perpetual, endemic infections of parasites and pathogens, and it is also

  likely that symptoms of disease arise in these colonies only when
they are

  weakened by adverse environmental circumstances, such as food shortages

  or damage to their nests. We will see, however, that the balance of power

  between the bees and their pathogens and parasites can be upset by intru-

  sive beekeeping practices, and that these practices can lead to severe losses

  of colonies. For example, a common feature of several diseases of honey

  bees—including American foulbrood and chalkbrood—is that the caus-

  ative pathogens persist over winter as resting stages on the combs. In na-

  ture, these combs would be cleaned by the bees in live colonies or de-

  stroyed by scavengers of the nests of dead colonies (e.g., the greater wax

  moth, Galleria mellonella). Either action would control the infections. But

  ever since beekeepers switched from using hives with fixed combs (such

  as skeps) to working with hives with movable combs (such as Langstroth

  hives), they have recycled the honey storage combs after extracting the

  honey from them. Beekeepers generally store the emptied combs away

  from the bees for the winter, which means that these combs are not natu-

  rally cleansed by the bees. Then in the spring, when they are returned to

  the bees, the combs can reinoculate the colonies with pathogens.

  A sad example of how beekeeping practices have disrupted some of the

  balances that once existed between honey bee colonies and their agents of

  disease is the recent rise in the virulence of the deformed wing virus. The

  history of this problem begins in the late 1800s, when beekeepers in the

  Russian Empire began exporting colonies of the western hive honey bee

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  ( Apis mellifera) from Europe to eastern Asia, specifically to the Primorsky

  region of the Russian Far East. This intercontinental transplanting of colo-

  nies occurred first by sailing ships but later via the Trans- Siberian Railway,

  which links Moscow and Vladivostok. Eventually, somewhere in the Pri-

  morsky region, the ectoparasitic mite Varroa jacobsoni underwent a host

  shift from colonies of the eastern hive honey bee ( Apis cerana), which is

  native to eastern Asia, to colonies of the western hive honey bee ( Apis mel-

  lifera), which had been introduced to eastern Asia. Then, after making this

  host shift, the population of Varroa mites living on the Apis mellifera colonies in the Primorsky region speciated into Varroa destructor. Because Varroa

  mites feed on the hemolymph (blood) of adult and juvenile honey bees,

  they are highly efficient vectors of the bees’ viruses, and this has created

  major health problems for colonies of Apis mellifera, especially those that

  live crowded in apiaries, where the mites and the viruses they carry spread

  easily among colonies. As will be explained shortly, the dispersal of Varroa

  mites and the deformed wing virus among unrelated colonies—so- called

  horizontal transmission—has favored the evolution of at least one highly

  virulent strain of the deformed wing virus.

  What follows is a look at how the lives of wild colonies and managed

  colonies of European honey bees differ in ways that affect the endless

  problem of colony defense. We will see that even though colonies living in

  the wild receive no human protection from predators, parasites, and

  pathogens, they tend to experience fewer problems—and incur lower

  costs—of colony defense relative to colonies living in apiaries.

  LIVING WITHOUT VS. WITH TREATMENTS

  FOR VARROA DESTRUCTOR

  Since the 1970s in Europe and the 1990s in North America, most beekeep-

  ers have found that they must routinely treat their colonies with miticides;

  otherwise they will die after a year or two from severe infections of viruses

  spread by Varroa mites, most importantly the deformed wing virus. In the

  last 10 or so years, however, several beekeepers and research biologists

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  have reported populations of European honey bee colonies that are thriv-

  ing without receiving treatments with miticides.

  Primorsky Kray, Russia

  One of these populations is a commercial line of honey bees available in

  the United States that is based on stock imported by the U.S. Depart-

  ment of Agriculture from the Primorsky Kray (region) of eastern Russia.

  As mentioned above, colonies of Apis mellifera were brought here from

  western regions of the Russian Empire starting in the late 1800s, and

  some time thereafter the mite Varroa jacobsoni made a host shift from Apis

  cerana to Apis mellifera. This host shift by the mites must have happened

  only rarely (possibly just once), because the gene exchange between the

  mites living on A. cerana and those living on A. mellifera was rare enough

  for these two populations of Varroa mites to diverge in morphology and

  behavior and eventually to live as two distinct species. The result is Varroa

  destructor, a mite that is, alas, superbly adapted for life as an ectoparasite of

  Apis mellifera.

  Once Varroa mites began to parasitize colonies of the European honey

  bees that had been introduced to eastern Russia, these bees began to un-

  dergo natural selection for resistance to these mites. Eventually, the colo-

  nies of Apis mellifera living in eastern Russia evolved a stable host- parasite

  relationship with Varroa destructor. The resistance mechanisms of these

  honey bees have been studied closely by a team of researchers led by

  Thomas E. Rinderer, at the Honey Bee Breeding, Genetics, and Physiology

  Research Laboratory in Baton Rouge, Louisiana. A series of studies started

  in the late 1990s has revealed that workers in colonies of Russian bees—

  compared to workers in colonies of stocks used commercially in the

  United States—are superior at grooming Varroa mites from their bodies,

  at removing mite- infested pupae from their cells, and perhaps also at bit-

  ing the legs off the mites. The net result is that populations of Varroa mites

  grow much more slowly in colonies of Russian bees than in colonies of

  U.S. domestic stocks (Fig. 10.1).

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  12,000

  s

  Domestic

  10,000

  Russian

  8,000

  6,000

  4,000

  2,000

  Mean number of adult female mite

  0 Jun Jul AugSep Oct Nov FebMar AprMayJun Jul AugSep Oct Nov

  1998

  1999

  Fig. 10.1. Infestation levels of Varroa destructor mites over time in colonies of

  Primorsky, or Russian, bees (black bars) and domestic colonies of North Ameri-

  can stock (white bars). The two types of colonies lived together in two shared

  apiaries.

  Gotland, Sweden

  The Russian bees demonstrate unequivocally that a population of Apis mel-

  lifera colonies of European origin can evolve mechanisms for survival de-

  spite being infested with Varroa destructor. Unfortunately, nobody tracked

  this evolutionary change, so we do not know how rapidly the bees’ resis-

  tance to Varroa mites evolved in eastern Rus
sia. In the early 2000s, how-

  ever, an answer to the question of how quickly resistance to Varroa mites

  can evolve emerged from a remarkable experiment that was conducted in

  Sweden under the leadership of the late Ingemar Fries, then a professor at

  the Swedish University of Agricultural Sciences. The goal of the experi-

  ment was to see whether Varroa mites “will eradicate European honey bees

  in an isolated area under Nordic conditions, where no mite control or

  swarm control of honey bee colonies are implemented.”

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  Fig. 10.2. One of seven apiaries that were set up in isolation on the south end of

  the island of Gotland, Sweden.

  This experiment began in 1999, when a population of 150 genetically

  diverse colonies—headed by A. mellifera mellifera, A. m. ligustica, and A. m.

  carnica queens from various sources in Sweden—was established in

  isolation on the southern end of Gotland, a 3,200- square- kilometer

  (1,200- square- mile) island in the Baltic Sea, about 90 kilometers (56

  miles) east of the Swedish mainland. These 150 colonies were distributed

  among seven apiaries (Fig. 10.2). Each colony was housed in a two- story

  Swedish hive, which is like a Langstroth hive, with two full- depth, 10-

  frame hive bodies. Once in place, the colonies were basically left alone and

  allowed to swarm. The only management was the feeding of a few colonies

  whose honey stores were insufficient for winter survival. Each colony

  started out free of Varroa mites but was inoculated with approximately 60

  mites when the investigators gave each colony 1,000 bees they had col-

  lected from mainland colonies heavily infested with the mites. Also, each

  colony’s queen was given a paint mark, so the investigators could detect

  turnovers in the colonies’ queens, usually due to swarming. The colonies

  were disturbed only four times each year, when inspections were made to

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  check for colony survival in late winter, colony size in early spring, colony

  swarming over summer, and mite infestation level in late October. Swarms

  from the colonies were collected during regular checks of the apiaries by

  a local beekeeper and by putting up bait hives. These swarms were installed