Note a very recent publication in ANIMAL BEHAVIOUR, 2006, 71, 161-171
doi:10.1016/j.anbehav.2005.04.009
How does an informed minority of scouts guide a honeybee swarm as it
flies to its new home?
MADELEINE BEEKMAN , ROBERT L. FATHKE & THOMAS D. SEELEY.
The authors posed the question of how the swarm knows in which
direction to fly, when only 5% of the bees, i.e. the nest-scouts who
had visited the new nest-site know where it is? The study used
man-made swarms, and prospective nest-sites in the form of small
wooden-hives, baited with one empty (apparently used) comb, and a lure
made of the major components of Nasanov-glands secretion. The authors
tested the vision hypothesis, (the possibility that the scouts
visually guide the swarm in the right direction by fast streaking
through the swarm, actually in the upper part of the swarm), vs the
olfactory hypothesis (the possibility that the scouts guide the swarm
by emitting odors from the 2 Nasanov-glands on their abdomen, so that
this results in an odor-gradient in the direction of the new
nest-site). To test the olfactory hypothesis the authors used swarms
where all the bees had the openings to their Nasanov-glands sealed. The
study showed that the treatment did not interfere with the ability of
the swarm to fly quickly and directly to the new nest, compared to
control-swarms with unsealed glands.
It is well-known that the scouts expose their Nasanov-glands once the
swarm reaches the new nest-site, and that the odors from the exposed
glands aid the swarm in entering the new nest. The results of the
study, however, led the authors to discard the olfactory hypothesis, as
far as guiding the swarm in flight is concerned. The vision hypothesis
also poses problems, because the "streakers" streak in the direction
of the new nest (for stretches of about 30 mm.), at a speed of about 10
m. per second, which is the fastest speed a swarm in flight achieve .
The swarm achieves this maximum speed only gradually, but the
"streakers" do not increase their streaking speed; which means that
they do not fly faster than other bees in the swarm, once the swarm
achieves maximal speed, so how could the streaking guide the swarm,
when the swarm has already achieved maximum speed?
The authors are, therefore, still faced with a mystery. There is,
however, a very simple solution to the problem, because the authors,
which the authors were unable to find because they failed to pose the
right wedded to the honeybee "dance language" (DL) hypothesis. This is
not surprising at all, since the
senior author, Thomas Seeley, has been known for years as a staunch DL
sup****ter.
The first one to discover that nest-scouts dance in the swarm, and to
study their behavior, and the behavior of the swarm, was Martin
LIndauer, v. Frisch's best known former student and collaborators, and
his work is, indeed, cited by the authors. LIndauer has naturally been
a staunch DL sup****ter. V. Frisch took it for granted that
food-foragers decide when to dance, depending on the quality of the
food, and the need for food in the colony. He knew that foragers never
dance in the absence of dance-attendants, but assumed that the foragers
know ("instinctively", or otherwise), that they should not waste time
and energy to dance unless they have an audience prepared to receive
the spatial information contained in the dances, about the site visited
by the foragers. (See v. Frisch's 1967 book.)
By the same token, Lindauer naturally took it for granted that
nest-scouts also decide when to dance, depending on the quality of the
prospective nest they found, and that other swarm-mates who attend
scouts'-dances then find the site by using the spatial information
contained in the dances. The swarm may have different groups of bees,
where each group "advertises" a different site in dances. But
eventually all dancing scouts end up advertising one and the same site,
apparently the best site found by any of the scouts.
Seeley, T. D. l(1977). Measurement of nest cavity volume by the
honeybee ( Apis mellifera). Behav Ecol Sociobiol 2:201-227
Seeley TD, Buhrman SC (1999) Group decision making in swarms,
eventually studied how nest-scouts evaluate the size of the cavity they
find.
He used apparently wooden, cylindrical boxes of various sizes, and
found out that when a nest-scout enters such a box, it crawls around
the cir***ference of the base, and that the scouts tended to dance more
often for his boxes that had a longer cir***ference of the base (which
meant also larger base, and a larger volume of the cavity).
He concluded that the scouts decide whether to dance, or not, based on
their *****sment of the volume of the cavity, and that they determine
the volume of the cavity by determining the area of the base, which
they achieve be measuring the cir***ference of the base.
To determine the length of that cir***ference by crawling along its
length, requires a counting ability. There is, however, no evidence,
and , therefore, no reason to believe that honeybees can count at all.
Apart from that, as I pointed out in ABJ (2000), vol. 140(1), Jan. pp.
12-13, the size of an area cannot be determined from the length of its
margins. The size of the area enclosed within margins of a specific
length is maximal, when the area is round, but may also be very small,
as long as it leaves a honeybee enough room to crawl around the
margins. Natural cavities, of course, do not occur in the form of
perfect cylinders, let alone perfect cylinders of the same height as
that used by Seeley..
I also pointed out that nest-scouts would not stand a chance of finding
the few natural cavities (in the trunk of a tree in the woods), that
are appropriate for a nest, if they were to simply examine just any
tiny hole out of the myriad of tiny holes that exist in their natural
environment. The scouts must, therefore, be attracted to specific tiny
holes, by the odors those holes have, which the holes share with odors
the scouts had learned to associate with a nest. In nature such
cavities, often resulting from a lighting-strike, have the odors of
"wounded" wood. Seeley's cylinders probably attracted the scouts by
wood-odors. Then, if the base had a longer cir***ference, the scouts ,
naturally, took longer to crawl along the cir***ference, which would
have resulted in their spending a longer period of time inside the
cylinder, and, thus, adsorbing onto their bodies a higher concentration
of the attractive odors in the cylinder.
Other factors, such as alien odors which repel the scouts, temperature
and light-intensity, winds, inside the cavity, undoubtedly also play a
role in the amount of time nest-scouts spend inside a cavity they
find. .V. Frisch (in his 1967 book,) had, however, already noted that
odors may play a role in attracting nest-scouts. But Seeley completely
ignored that.
Honeybees (whether foragers, or nest-scouts), never decide whether to
dance, or not. The dance results from an escape by bees carrying
attractive odors, from hive-mates, or swarm-mates, who chase after
them, after being attracted by the odors such bees carry. In the case
of successful nest-scouts, some swarm-mates are attracted by the odors
the scouts carry on their bodies, from the cavity they found; which are
the odors that attracted the scouts to the cavity in the first place.
Some of the dance-attendants then find the same cavity, but they do so
by use of odor alone all along. The odors they carry back to the swarm
then attract other swarm-mates, and the new bees that found the cavity,
thus, become additional scouts that "advertise" that cavity.. Swarm
bees very gradually come to prefer the scouts that carry more
attractive odors. The scouts that carry less attractive odors are,
thus, not chased any more, and, therefore, do not dance either. They
may themselves be attracted by the odors carried by the scouts that
bring back to the swarm more attractive odors, and eventually find the
cavity visited by the scouts that bring in the most attractive odors.
This is how a "consensus" is reached, where there is only one large
group of nest-scouts, all advertising one and the same cavity.
Bees in a swarm are attracted visually, as well as by odors, to other
swarm-mates, as well as to odors from the queen (which most of them
cannot see). This is how the swarm keeps together. Swarm bees are,
however, also attracted by the odors nest-scouts carry on their bodies.
It is these odors, which are adsorbed onto the scouts' bodies, and
gradually wash off as the scouts fly with the swarm, that create the
odor-gradient that leads swarm-bees in the direction of the cavity. The
scouts expose their Nasanov -glands only after they land at the
entrance to the cavity. I have never seen any re****t by anyone who saw
them expose those glands while flying with the swarm. The scouts
attract swarm-mates only by the odors adsorbed onto their bodies, and
sealing the Nasanov-glands of all the bees in the swarm, therefore,
should not have any effect on the swarm's-flight to the new nest; as
the study showed.
The authors knew they had deliberately used in their prospective nests
odors that attract nest-scouts. However, the possibility that such
odors, that adsorb onto the bodies of scouts that visit such a
prospective nest, are the odors that also attract swarm-mates, which
results in the dances of nest-scouts, and then, when there is a large
enough number of scouts which all carry the same attractive odors,
which suffice to attract the whole swarm to fly with them, has never
occurred to the authors. The olfactory hypothesis needs to be rejected
only in the version the authors tested, which depends on odors emitted
by the scouts' Nasanov-glands. Other than that, an olfactory hypothesis
which depends on odors from the cavity, that are adsorbed onto the
scouts'-bodies, appears to be a very simple solution, and the only
proper solution to the problem.
The case only goes to show ever new trouble that is caused by the
belief that honeybees have a DL!
Sincerely,
Ruth Rosin ("Prickly pear")
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