capping times

[MichaelW]

Has this older computer population model study been discussed?

A population model for the ectoparasitic mite Varroa jacobsoni in honey bee (Apis mellifera) colonies
Stephen Martin*
National Bee Unit, Central Science Laboratory, Sand Hutton, York, YO4 1LZ, UK
Received 9 October 1997; accepted 4 February 1998. Available online 13 July 1998


"4.5. Effect of decreasing the host sealed-brood period
The idea that bees with a shorter sealed period are more resistant to the mite has been the focus of much research and bee breeding programmes. By combining the offspring mortality data (Table 3) with their developmental times (Martin, 1995b) the effect of shortening the sealed brood period on the mite population development was investigated. Fig. 6 indicates that even a 1-day reduction in the sealed brood period would only delay and not prevent the mite build-up. The model indicates that unless worker post-capping times approaching 9 days can be achieved it is unlikely that selecting bees with shorter capping times would give rise to mite-tolerant bees (Martin, 1997b). However, if shorter post-capping times are associated with increasing levels of mite mortality both within the cells and shortly after emergence (Calis et al., 1996) worker post-capping times more than 9 days may prevent mite populations increasing, but data on offspring mortality levels is needed to test this idea. "

link (http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VBS-3T52SPP-4&_coverDate=06%2F22%2F1998&_alid=411691041&_rdoc=1&_fmt=&_orig=search&_qd=1&_cdi=5934&_sort=d&view=c&_acct=C000019958&_version=1&_urlVersion=0&_userid=422010&md5=4f5006c1c5467bf10c76637e8e093d1a#toc22)

[MichaelW]

If you then look at this study

Reproduction of Varroa destructor
in South African honey bees: does cell space influence
Varroa male survivorship?
Stephen J. MARTINa*, Per KRYGERb
a Laboratory of Apiculture and Social Insects, Department of Animal and Plant Sciences, University
of Sheffield, Western Bank, Sheffield, S10 2TN, UK
b Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa
(Received 18 May 2001; accepted 27 October 2001)

"One consequence of space partitioning
in Varroa sp. is that the first (male) egg
is laid near the cell cap. This increases the
survival probability of the male mite since it
is the only place in the cell not affected by
the bee’s molt (Fig. 2). However, the male
mite must now pass the constriction caused
by the bee’s appendages to reach the feeding
site which is established by the mother
mite on the bee’s abdomen (Fig. 2). Since
only one male is produced per batch of
eggs, its death will result in all the female
offspring being unmated and so unable to
produce offspring"

You could say that the factor of a bee in a tight cell might help push the computer model to longer than 9 days.

A stretch?

[ June 08, 2006, 11:42 AM: Message edited by: MichaelW ]

[Michael Bush]

Not counting the possible affect on the male mite, ( http://www.edpsciences.org/articles/apido/pdf/2002/01/Martin.pdf?access=ok )the shorter capping time, and shorter post capping time on small cell seems to make a heck of a dent. Capped in 8 days and emerged in 19.

http://www.bushfarms.com/beesnaturalcell.htm

This model:

http://www.csl.gov.uk/science/organ/environ/bee/varroa/ModellingBiologicalApproaches.pdf

says:

"Shortening the post-capping time
Shortening the post-capping time reduces the number of offspring
that can be produced and the time for the last offspring to
successfully mate prior to emergence. Post-capping periods for
worker European bees have been reported to vary from 268 to 290
hrs (Harris and Harbo 2000) and the model is based on a post-capping
period of 288 hrs for workers and 336 hrs for drone brood.
Worker Africanized bees usually have a post-capping period 20
hrs shorter than European bees (Rosenkranz 1999). However,
among European bees there is significant variation in the average
duration of the capped period and this is a heritable characteristic
(Harris and Harbo 2000), but it can be affected by climatic conditions.
European Apis mellifera carnica bees had a worker postcapping
time only 8 hrs longer than Africanized bees at the same
tropical site (Rosenkranz 1999).
The model predicts that, in order to bring about a 25% reduction
in mite population growth (excluding the possible effects of
reduced mating success and fertility of daughter mites) the postcapping
period for worker brood needs to be reduced by 7% (20
hrs) for worker brood, by 9% (30 hrs) for drone brood and by 7%
(20hrs worker, 24hrs drone) for both. This results in a post-capping
time close to the minimum reported for worker brood, but
drone brood has greater phenotypic variation (de Jong 1997) suggesting
that it may be possible to breed bees that produce drone
brood with a shorter post-capping period. Buchler and Drescher
(1990) reported that 25% of the variation in mite populations in
their colonies could be accounted for by variations in the post-capping
period, which fits in well with the results of our model.
However, in a survey of European bees an average 8.7% reduction
of mite infestation rate was calculated for each 1hour reduction in
the capping time (de Jong 1997). This is a much larger effect than
our model predicts, suggesting other factors are confounding the
comparison in European bees."

This would indicate that a post-capping period that is 20 hours shorter would make the 25% difference that they think is critical to surviving mite infestations.

and also:

"Altering the invasion rate of brood cells by the mite
The model suggests that the invasion rate of worker cells would
need to be decreased by 96% to reduce the mite population growth
rate by 25% (Table 1). Such a large reduction is necessary because
mites which do not enter worker cells are available to invade drone
cells. Since mite reproduction is greater in drone cells, only a proportion
of these "displaced" mites need to enter drone cells to balance
the loss of population growth. The attractiveness of the brood
to varroa mites may be affected by a number of factors which may
interact, including the size of the cell and the strength of the
pheromone signal."

And on the effect of cell size and invasion rate and pre capping times:

"The size and shape of the brood cells
The diameter of the worker cell appears to affect the invasion of
varroa mites. In the absence of drone brood, the varroa infestation
rate has been reported to be 16-50% lower in the small Africanized
worker cells than in the larger European (Italian) worker cells
(Guzman-Novoa et al. 1999, Rosenkranz 1999). This in part may
have been due to a higher visitation rate by nurse bees as the
European larvae were larger and heavier, and to the longer periods
spent capping the larger cells which would increase the time period
over which a mite can invade the cell (Message and Goncalves
1995)."

Another study I heard quoted at "Beetopia" here in Lincoln, was about how the majority of the mites get into the cell during the last 24 hours that it is uncapped and a shorter capping time could help with controling the reproduction of the mites. I didn't get the details of where to find the study, but the presenter wasn't thinking of small cell, but of possible genetic traits. The Harbo study mentioned above correlates capping and post capping times to genetics and climate, but there are studies correlating it to cell size. (see the one at the top) I have observed a one day shorter capping time (8 days) with small cell bees.

Also the model above assumes a 288 hour post capping time (12 days). I have not observed any longer than a 11 day post caping time on my small cell workers.

I have the official State inspection certificate here for my untreated small cell hives and for the third year in a row the varroa were below detectable levels. For the third year in a row the inspection of all hives in my home yard found no varroa in any of them. So whether that is because of male survivorship or because of shorter capping and post capping times, it seems to work.

Any mathematical model will make some assumptions. Some will be correct. Some will not. Some will be significant. Some will not. Theory is a wonderful place. Everything works there. smile.gif

[wayacoyote]

Good discussion. We talked some about this when the state apiarist visited the association last week. However, he took a different approach than comparing Europeans to Africanized bees as these studies do. He compared European bees to Asian bees in which the capping times are so significantly shorter that "the varroa don't even bother" to attempt to utilize the worker brood. To me, this means NO varroa in worker cells.

My questions include:
How does the varroa choose between the cells? (perhaps like the queen... using her front legs? I jest)
How can this knowledge be utilized to benefit us keeping European bees?

Waya