Thelytoky in Honey Bees
Both the original document and I have drawn on various
sources for the following information although the majority comes from
the Carl Hayden document. These sources are noted at the bottom of
the page, if I have missed any, I apologise.
Basically, Thelytoky is... the ability to rear workers and
queens utilising the eggs from laying workers, or in some cases
virgin queens. This subject has in the past been considered a rarity
that only occurs in the Cape bee, apis mellifera capensis Escholtz,
but it has been found in other strains.
It does occur in the European apis mellifera xxx strains but
with considerably lower frequency. [1] In queenright colonies
development of most worker ovaries is suppressed by the pheromone
9 - oxy - decenoic acid and possibly other substances emitted by the
queen, [2] as well as substances possibly emitted by unsealed brood.
[3] Workers can develop ovaries and some can lay eggs in the absence
of both queen and open brood. [4]
European laying workers generally produce unfertilized
haploid eggs that give rise to drones (if they develop at all).
It is rare, but there are instances of both virgin queens and laying
workers producing diploid eggs and those that develop, produce true
female worker or queen bees. [5]
What causes Thelytoky? First a biological mechanism is
needed to produce viable diploid eggs. Secondly various natural
control systems need to be bye-passed or modified {see worker
policing (link)}. The biological mechanism is a gobbledygook
sentence that I will reproduce here,
"Cape bee workers lay
unfertilized diploid eggs because during ana-phase II the egg
pronucleus and the central descendent of the first polar body fuse
to form a diploid zygote nucleus." [6]
But the behaviour modification is more difficult to understand!
I offer various quotes and elements of the original text
that I hope will aid understanding...
"Given the high frequency of thelytoky in Cape bees, the relatively
rare occurrence in domestic stocks of European bees is unexpected,
since populations capable of thelytoky have an advantage over those
in which laying worker eggs develop exclusively into drones." (Ruttner
1977) {This may now be better understood due to the recent work on
worker policing by Francis Ratnieks at Sheffield University.}
"Without thelytoky, the survival of a colony rests completely
on the successful mating of a single queen which must leave the hive
to mate. If this queen does not encounter drones or does not return
to the hive, a replacement cannot be produced because female larvae
of a suitable age for queen rearing no longer exist, and because the
first queen to emerge usually destroys the other queen cells in the
colony. However, if brood from laying workers could be raised into
queens the colony would have a facultative survival mechanism in
case the virgin queen is lost. Thelytoky should occur with greater
frequency in populations exposed to conditions that reduce the
chances of a queen mating." (Moritz 1984)
"Reports indicate that in managed colonies thelytoky is expressed at a
very low frequency" (Mackensen 1943). The reasons given for this
statement are given below.
"Beekeeping practices inadvertently select
against thelytoky. For example, swarming and supersedure can be
minimized through various management techniques, and thus the
possibility of a colony becoming queenless due to the loss of a
virgin queen can be reduced. If colonies lose their queens and do
not have brood to produce replacements, the queens often are
replaced with new ones by beekeepers. Hence, there is no selective
pressure for thelytoky in colonies managed in this manner.
Conversely, the conditions under which the LUS strain was derived
may have inadvertently selected for thelytoky. Virgin queens
introduced into broodless colonies during the winter may not have
been accepted by the workers in some cases, while in others the
queens may not have mated or were lost on mating flights. Some of
the colonies that survived may have done so because they requeened
themselves with brood from laying workers. The winter requeening
procedure was repeated annually using queens produced from brood of
colonies that survived the previous year's winter requeening. If
thelytoky was originally at a low frequency in the LUS strain at the
beginning of the breeding program, the frequency possibly was
increased because of continued selection followed by the production
of new queens from brood of the survivors."
"Sometimes during an inspection bees were seen biting each other, or
with their abdomens in the cell assuming an egg laying position. We
sampled LUS bees being bitten and dissected them to determine if they
had ovary development. Whether workers assuming the egg laying
position always deposited an egg in the cell also was determined."
"Once all the brood emerged in queenless LUS, CP, or cd (control)
colonies, worker bees were scattered over the frames giving the
colony the distinctive appearance associated with the queenless state.
Upon closer examination of bees from the 4-5 frame nucleus colonies
and in the observation hives sometimes workers were seen grasping
each other with their mandibles."
"In a LUS observation colony, workers
were seen pulling nestmates out of the cells in which they had
inserted their abdomens. On other occasions, in the observation
hives we saw eggs being eaten by nestmates immediately after the
laying worker removed her abdomen from the cell."
"A queen produced from laying
worker eggs successfully mated and produced worker and drone brood.
However, eight of the nine queens produced from workers' brood
either did not return to the hive after a mating flight, or were
critically injured during artificial insemination."
"A honey bee colony's ability to requeen itself with the eggs of laying
workers requires not only that some workers can lay diploid eggs, but
that the workers can foster the cooperation from nestmates needed to
construct a queen cell and rear the egg into a queen. When laying
workers developed in CP or cd colonies, often queen cells were
constructed and sometimes eggs were deposited inside them. However,
the eggs were either cannibalized by other workers or left unattended
(untended) and did not hatch."
Possible flaws in this work
- That there was already existent in the LUS strain abnormally
large numbers of genes from apis mellifera capensis. Such genes could
have been filtering into the area of the trial over many years but at
such a low rate that the colonies concerned went unrecognised.
- There is the possibility that the quantity of the thelytoky genes
(from whatever source) was enhanced by other management, out of
season breeding, the use of small celled foundation, selection of
queens for shorter development times. Any or all of these may have
had an effect.
- In the case of virgin queens laying diploid eggs there could have
been a fleeting, incomplete mating that passed a small number of
sperm to the queen which at later dissection were not noticed or the
few sperm were "used up" in fertilising the few eggs laid.
- I consider it possible (but unlikely) that sperm could exist in a
"loose" state from accidentally crushed drones, but I can also see
many obstacles to those sperm ever being in a position to fertilise an
egg, from any source, even if they survive the exposure.
References
[1] Onions 1912, Jack 1917, Anderson 1963, Ruttner 1976
[2] Butler and Fairey 1963
[3] Kropacova and Haslbachova 1971
[4] Perepelova 1929, DeGroot and Voogd 1954, Butler 1957,
Butler and Fairey 1963, Jay 1970, Kropacova and Hasibachova 1970 & 1971
[5] Mackensen 1943
[6] Verma and Ruttner 1983
Other References... Suomalainen 1950
The Work was carried out by... Dr. Gloria DeGrandi-Hoffman, Dr. Eric H.
Erickson Jr.
Of... Carl Hayden Bee Research and Biological Control Center, Tucson,
Arizona, USA
And was published 29 January 1991
The LUS strain of bee was selected by:- Delores and Edward Lusby who
are commercial beekeepers working in Tucson, Arizona.
I have been selective in what I have taken from the
original text, this selectivity is intended to simplify rather than
mislead.
The original
document on beesource.com is available on this link and it
should be consulted if you require more details.
THIS PAGE IS A BETA EDITION AND MAY CONTAIN ERRORS
Revised... 20 June 2001
