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Apiacta, Feb. 1984 - pages
165-167
DE RUIJTER, A. (Netherlands)
Reproduction of Varroa only occurs inside capped worker
and drone brood cells. Prior to reproduction, female mites leave
the adult bees and enter brood cells just before capping. The
mites enter the larval food and stay there until the bee larva
frees them by eating the food. At this time, the cell has been
capped. More mites are found in drone cells than in worker cells.
There seems to be chemical attraction which is stronger in drone
larvae than in worker larvae. In queenless colonies, more mites
were found on drone pupae in drone cells than on drone pupae
in worker cells. In Brazil, more mites were found in large worker
cells than in smaller ones. These two observations indicate that
features of the cell are important in respect of distribution
of Varroa on the comb.
In our first experiment, we tried to establish this by offering
different types of cells on one comb to Varroa-infected colonies.
Feeding on the larva inside the capped brood cell initiates oviposition.
It has been demonstrated that application of juvenile hormone
to honeybee larva, just after cell capping, stimulates the reproduction
of Varroa. Oviposition starts 60 hours after cell capping.
An egg is laid about every 30 hours. As a rule, the first egg
is female, the second male, the third and following eggs are
also female. Females develop from fertilized eggs and are diploid,
males develop from unfertilized eggs and are haploid.
In our second experiment we studied factors influencing the pace
of oviposition and the success of reproduction.
Experiment 1.
Material and methods
We put drops of melted beeswax in a worker comb in a regular
pattern into certain cells: in every fourth horizontal row of
cells, every fourth cell was made 3 to 4 mm less deep than neighbouring
cells. This comb was placed inside the broodnest of a Vurroa
infected colony. When most of the brood was capped, we examined
the contents of treated and untreated cells. We scored the number
of adult Varroa females that had entered the different
cells. This was done separately for five age classes of the bee
brood, according to Ifantidis.
Results and discussion
The preference is always bigger than one (mean=6.97), except
for one observation where the number of treated cells was very
low. This means that adult female mites enter protruding cells
more frequently than normal worker cells, though all cells
contain worker brood.
Conclusion
Apparently chemical attraction is not the only factor that
determines the distribution of mites in available cells; cell
type is also important. The mechanism by which the mites discriminate
between different cell types is not clear. Probably. the behaviour
of the bees that carry the mites to the brood cells is different
towards different cell types. The process of leaving the bee
and entering the brood cell needs further study. Intervention
in this process might lead to biological control.
Table
1.
Number of Cells Examined and Mean Numbers of Adult Female Mites
per Cell for Each Age Class of Bee Brood |
| Age
class of the bee brood* |
Untreated
cells |
Treated
cells |
Preference**
(B/A) |
|
Number of cells |
Mean number of adult
female mites per cell (A) |
Number of cells |
Mean number of adult
female mites per cell (B) |
| I |
153 |
0.013 |
25 |
0.080 |
6.1 |
| III |
199 |
0.005 |
44 |
0.091 |
18.2 |
| IV |
133 |
0.038 |
10 |
0.200 |
5.3 |
| II |
52 |
0.019 |
9 |
0.222 |
11.6 |
| III |
49 |
0.041 |
11 |
0.564 |
8.9 |
| III |
106 |
0.283 |
18 |
0.556 |
2.0 |
| IV |
159 |
0.264 |
50 |
1.280 |
4.8 |
| II |
47 |
0.0532 |
6 |
2.667 |
5.0 |
| III |
26 |
0.731 |
3 |
0.667 |
0.9 |
* I=prepupa, II=pupa
with white eyes, III=pupa with red eyes, IV=pupa early tanning,
V=pupa with brown thorax.
** The mean number of mites in treated cells divided by mean
number of mites in untreated cells is given as "preference". |
Table
2.
Mean Offspring of Females Confined in a Newly-capped Drone or
Worker Cell and then Put in a Newly-capped Worker Cell |
|
Period in brood cells: |
Number of cells |
Egg/
larva |
Protonymph |
Deutonymph |
Adult |
|
Mobile |
Immobile |
Mobile |
Immobile |
|
24 hrs drone + 9 days
worker |
n=19 |
0.0 |
0.5 |
0.6m |
0.9m |
1.8m |
0.9f
0.8m |
|
48 hrs drone + 9 days
worker |
n=10 |
0.2 |
1.0 |
0.1m |
1.3m |
1.1m |
1.7m |
|
48 hrs drone + 7 days
worker |
n=15 |
0.7 |
0.7 |
0.2m |
1.7m |
1.1m |
|
m = male
f = female |
Experiment 2.
Material and methods
Open worker brood cells were
marked by a sheet of transparant plastic, attached to the frame
by two drawing pins. The comb was then put back into the colony.
After 4 hours, newly-capped cells were numbered and opened by
using a razor blade. A female Varroa mite was introduced
into each cell, the cells were carefully closed and the comb
placed back in the colony again. After a desired period the cells
were opened and the content studied.
We tried to increase the stimulation of oviposition by transferring
mites 24 or 48 hours after cell capping into newly-capped cells.
In this way, the mites were able to feed on round larvae and
spinning larvae twice and would get a double amount of any factor
in the haemolymph of the bee.
Results and Discussion
After 24 hours extra in a worker
cell or drone cell, a male is produced in most cases. Apart from
an adult female, in many cases there are 3 female deutonymphs.
Compared to 10 days, the intervals between the successive eggs
must have been shorter.
After 48 hours extra in a worker or drone cell, no males are
produced at all. In many cases there are three deutonymphs (means
are 2.4 and 3.0). This again suggests that the interval between
successive eggs is shorter than in the normal situation.
Conclusion
Oviposition, as well as sex determination are affected by stimuli
during the first two days inside the capped brood cell.
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