to water sources, so they can meet their water needs without maintaining
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240 Chapter 9
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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242 Chapter 9
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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244 Chapter 10
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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Colony Defense 245
( 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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246 Chapter 10
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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Colony Defense 247
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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248 Chapter 10
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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Colony Defense 249
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
The Lives of Bees Page 30