1 of 34

VARROA DESTRUCTOR

FDBKA 7 November 2024

By Alan Baxter

2 of 34

CONTENT

The origins and biology of Varroa destructor

What happens to your bees when Varroa feeds on them

Varroa and the viruses that are vectored by Varroa

The treatments to reduce the varroa load

Parasitic mite syndrome

Monitoring for mite levels

Treatment-free colonies

3 of 34

WHAT IS VARROA

An ectoparasitic mite

of honey bee brood

4 of 34

Native to southeast Asia.

Co-evolved with the Asian honey bee Apis cerana.

Apis mellifera introduced into Japan & Russia in the 19^th C.

Varroa spread into A.mellifera.

First found in A.m. in Japan in 1957.

Now found in most countries in the world.

5 of 34

6 of 34

Why is it bad for our honey bees and not the Asian ones?

Brood parasite – feeds on the fat body of the pupa.

A.cerana only feeds on drone brood

Grooming and hygienic behaviours to remove the mites.

Neglect drone brood. Mites entombed and die.

7 of 34

In Europe varroa feeds on both drone and worker brood

European bees don’t entomb the infected brood

Don’t have the evolved hygienic behaviours of the Asians

Open season for the mites

8 of 34

Varroa female – foundress - lays egg

Punctures the larva to establish a feeding point.

60 hours later the first egg develops into a male

30 hour interval more eggs which develop into females

Male mates with his sisters

New bee emerges with female mites

Male mite dies in the cell

Worker bees emerge after 21 days – average 1.5 new mites

Drones emerge after 24 days – average 2.6 new mites

Life cycle

9 of 34

10 of 34

POPULATION DOUBLES EVERY 21-24 DAYS

11 of 34

12 of 34

Effects

Bite on the pupa

Wound allows bacteria to accumulate – infected

Infested pupae have weight reduction

Proteins in mite saliva inhibits wound healing

Mites carry the DWV virus which enters through the wound

Suppress immune system.

13 of 34

DEFORMED WING VIRUS (DWV)

14 of 34

DWV

Transmitted at low levels from parent to offspring or adult to adult is less virulent.

When transmitted by mouthparts of varroa more concentrated dose.

Acute lethal infection in pupa.

Chronic infection in adult bee.

15 of 34

OTHER JOLLY VIRUSES

Acute bee paralysis virus

Cloudy wing virus

Slow paralysis virus

Israeli acute paralysis virus

Colony collapse disorder

16 of 34

PARASITIC MITE SYNDROME

17 of 34

PARASITIC MITE SYNDROME SIGNS

Nibbled or perforated cappings

Chewed or cannibalized pupae

Dead pupae

Adults with deformed wings

Spotty brood pattern

Supersedure cells

Neglected brood

Aggression

18 of 34

Regular testing/monitoring

IPM

Drone Brood uncapping/removal

Comb trapping

Oxalic acid – gas vap

Miticides*

Shook swarm

Collected swarms (in quarantine)

PREVENTION

19 of 34

20 of 34

Check your varroa board regularly

21 of 34

Monitoring period 7 days
Count the number of mites and divide by 7
Multiply the daily drop by one of the following:

November to February x 400
May to August x 30
March, April, September, October x 100

Maximum threshold of mites per colony: 1,000.
Treatment should begin before this level is reached

NBU GUIDELINES

22 of 34

Sugar roll

300 Bees

Caster sugar

Roll container

Shake onto white surface

Divide by 3

Less than 3%

23 of 34

CO2

300 bees

Whiff of CO2

Count the mites & divide by 3

Return bees to hive

24 of 34

Alcohol wash

25 of 34

TREATMENTS

Essential oils

Thymol

Other botanical oils

Organic acids

Oxalic acid

Formic acid

Synthetic pesticides

Amitraz

Tau fluvinate

Flumethrin

26 of 34

TIMING OF TREATMENTS

Winter – broodless period – Oxalic acid

Spring – as needed – Miticide or Oxalic acid

Late summer – Miticide after honey harvest

Collected swarms – broodless period -Oxalic acid

After shook swarm - broodless period - Oxalic acid

27 of 34

Best spring treatment

Drone brood removal

Best summer treatment

Formic acid

Best autumn treatment

Apiguard

Best winter treatment

Oxalic acid

ALWAYS FOLLOW THE MAKER’S INSTRUCTIONS TO THE LETTER

28 of 34

29 of 34

TREATMENT FREE

Apis mellifera did not evolve with Varroa destructor

New pest introduced to a naïve population

Can result in population crash

Feral colonies swarm regularly so have a regular brood break and a new home

Honey bees kept in hives are managed livestock

30 of 34

Things to consider

It involves the death and suffering of a lot of honey bees

The survival rate of infested colonies is low

Infestation impacts neighbouring apiaries

Gotland – no treatment for 20 years – isolated island in Baltic Sea

Selective breeding programme over very long period

31 of 34

32 of 34

SUMMARY

Varroa destructor is a serious menace to our colonies of honey bees

Exponential growth leads to rapid death of a colony if not dealt with

A mixture of chemical and non chemical interventions

can keep it under control

Varroa is a parasite of brood

Vector for some nasty viruses

33 of 34

34 of 34

QUESTIONS