www.omlet.co.uk
Page 47
How do the mites live?
Varroa are external parasites that live exclusively on honeybees, feeding
on their haemolymph (blood). To breed, a mated adult female mite nips
inside a brood cell just before the cell is capped over. She hides in the
brood food until the cell is sealed and then feeds on the developing bee.
The female mite lays between 5-6 eggs. One of these eggs is a male mite,
which mates with the females when they hatch. The male dies when the
cell is opened and any unmated females are therefore sterile. With heavy
infestations, numerous female mites may enter the same cell to breed.
The mites have a preference for reproducing within drone brood because
these take longer to hatch than worker brood and the mites therefore
have more chance of mating successfully.
During the summer, female varroa
mites may live for 2-3 months. In
winter, when there is no brood, the
mites live on the bodies of the adult
bees within the winter cluster. When
the queen starts laying eggs again
the following spring, the mites once
again start breeding in the brood
cells. Mites cannot survive more than
a few days without bees to feed on
(e.g. on combs or equipment).
What effect do mites have on bees?
Having a blood sucking parasite on you while you are trying to develop
is a big disadvantage. A larva in a cell which is infested with varroa mites
will usually survive but may be smaller, have deformed wings or other
abnormalities. As well as causing physical damage, by weakening the
larvae and adults by feeding directly upon them, varroa mites also act as
a transmitter for a number of honey bee viruses. Colonies weakened by
heavy varroa mite infestation will be much less able to cope with disease
than a strong colony.
A bee with poorly developed wings.
The inspection tray provides useful information about the health of your
bees. It can be used to monitor the number of varroa that are in your
bees and also examine any debris that has fallen from the hive. You can
keep your inspection tray in all year around, however you should check it
and empty it regularly to avoid a wax moth infestation.
Removing your inspection tray.
An inspection tray with debris.
Using your inspection tray
Monitoring varroa with the inspection tray
Ideally, you should monitor the amount of varroa at least four times
each year: early spring, after the spring honey flow, at the honey harvest
(usually in August/September) and in late autumn. The accepted safe
level of varroa mites in a colony is 1000 mites. However, at this level, the
signs of infestation are not obvious from simply inspecting the combs and
when damage to adult bees becomes apparent (shrivelled wings) the
infestation is well advanced.
There are two main ways of estimating the total number of varroa mite
in the colony.
1. Natural mite drop.
2. Drone brood inspection.
Natural mite drop
Counting the number of mite that die naturally gives you a good estimate
of the total number of mites in the hive. Start by putting the inspection
tray under the Beehaus when you inspect your bees. Leave the tray in
place for 5-7 days and then inspect it. Count the number of mites on the
tray and then divide by the number of days it was in place to calculate the
daily mite drop. For example if the tray was left in for 5 days and 20 mites
were counted the daily mite drop is 20/5 = 4 mites per day.
The critical daily mite drop varies throughout the season as follows:
MONTH
CRITICAL DAILY
MITE DROP
January
0.5
February
0.5
March
0.5
April
0.5
May
6
June
10
July
16
August
33
September
20
October
10
November
0.5
December
0.5
Drone brood inspection
Whenever the colony has brood, 80% of the mites infecting the colony
are in the sealed brood. The female mites prefer to lay their eggs in the
larger dome capped cells containing drones. To estimate the number of
varroa this way you need to uncap and remove about 100 drone larvae.
The colony is heavily infested by varroa if more than 5 drone larvae have
varroa visible on them. This inspection is only really an option during the
spring and first part of the summer when the queen will be laying plenty
of drones.
Varroa treatment is covered on the following page.
