Varroa mite migration into colonies: how it increases mite populations

and presents new problems for Varroa control

Gloria DeGrandi-Hoffman, *Fabiana Ahumada , Victor Zazueta , Mona Chambers,

Geoffrey Hidalgo and Emily Watkins deJong Carl Hayden Bee Research Center, USDA-ARS, Tucson, AZ

*AgScience Consulting, Tucson, AZ

Why are Varroa such a problem?

• Reproductive rates are not very high

– Each invading ‘mother mite’ can produce about 1.5 mated female offspring in worker cells and 2.7 in drones (Fries et al. 1994; Martin 1998).

• Takes 2-3 years before populations impact colonies (Boecking and Genersch 2008; Genersch 2010;

Rosenkranz et al. 2010).

Honey bee and Varroa mite population dynamics model

VARROAPOP Program

DeGrandi-Hoffman G, and Curry R (2004) Int J Acarol 30:259–274

Mite population growth

DeGrandi-Hoffman G, and Curry R (2004) Int J Acarol 30:259–274

Mite and colony population growth Miticide applications in August each year

Mite population

DeGrandi-Hoffman G, and Curry R (2004) Int J Acarol 30:259–274

What’s happening now (treat in April and then September)

Varroa Population Growth

0

5

10

15

1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct

Actual

Predicted

5000

20000

35000

50000

1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct

Actual

Predicted

0

2

4

6

8

1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct

Actual

Predicted

Adult bees Frames of brood

Mit

es

pe

r 1

00

be

es

Mites per 100 bees

DeGrandi-Hoffman et al. 2014 J. Appl. Exp. Acar. 64: 171-186

Mite migration

• Reports in the literature: – Sakofski F, Koeniger N, Fuchs S (1990) Seasonality of honey bee colony

invasion by Varroa jacobsoni Oud. Apidologie 21:547–550 – Kraus B, Page RE Jr (1995) Population growth of Varroa jacobsoni Oud. in

Mediterranean climates of California. Apidologie 26:149–157 – Delaplane KS, Hood WM (1999) Economic threshold for Varroa jacobsoni

Oud. in the southeastern USA. Apidologie 30:383–395 – Kralj J, Fuchs S (2006) Parasitic Varroa destructor mites influence flight

duration and homing ability of infested Apis mellifera foragers. Apidologie 37:577–587

– Frey E, Schell H, Rosenkranz P (2011) Invasion of Varroa destructor mites into mite-free honey bee colonies under controlled conditions of a military training area. J Apic Res 50:138–144

– Frey, E. Rosenkrantz. 2014. Autumn invasion rates of Varroa destructor (Mesostigmata: Varroidae) into honey bee (Hymenoptera: Apidae) colonies and the resulting increase in mite populations. J. Econ. Entomol. 107(2): 508-515

Examining the role of migration on mite population growth

• Started with package bees – 2 sites, 20 colonies per site

• Monitored mite populations starting before first sealed brood

• Monitored colony population growth

• Measured the proportion of foragers with mites

– incoming and outgoing

Colony set up for mite migration measurements

Measuring migration

Mites on foragers site-1

0

0.02

0.04

0.06

11-Aug 11-Sep 11-Oct 11-Nov

mites out

mites in

0

0.02

0.04

0.06

11-Aug 11-Sep 11-Oct 11-Nov

mites out

mites in

AM PM

Pro

po

rtio

n o

f fo

rage

rs w

ith

mit

es

Pro

po

rtio

n o

f fo

rage

rs w

ith

mit

es

Mite population growth

site-1

0

2

4

6

May June July Aug Sept Oct Nov

actual

predicted

0

3

6

9

May June July Aug Sept Oct Nov

actual

predicted

mit

es

pe

r 1

00

be

es

%

of

infe

ste

d c

ells

Mites per 100 bees % of brood cells with mites

Mites on foragers Site-2

0

0.02

0.04

0.06

11-Aug 11-Sep 11-Oct 11-Nov

mites out

mites in

0

0.02

0.04

0.06

11-Aug 11-Sep 11-Oct 11-Nov

mites out

mites in

Pro

po

rtio

n o

f fo

rage

rs w

ith

mit

es

Pro

po

rtio

n o

f fo

rage

rs w

ith

mit

es

AM PM

Mite population growth

Site-2

Mit

es

pe

r 1

00

be

es

0

2

4

6

April May June July Aug Sept Oct Nov

actual

predicted

0

3

6

9

May June July Aug Sept Oct Nov

actual

predicted

% o

f in

fest

ed

ce

lls

Mites per 100 bees % of brood cells with mites

Location Predictor p

Site-1

Site-2

frames of adult bees

frames of brood

infested cells (mites / 100 cells)

foragers with mites

frames of adult bees

frames of brood

infested cells (mites / 100 cells)

foragers with mites

0.036

<0.0001

0.811

<0.0001

0.507

0.162

0.839

0.012

Factors affecting Varroa population growth

If foragers with mites affects Varroa population growth, what does this

mean for mite resistant lines?

Collaboration with Drs. Tom Rinderer and Bob Danka

USDA-ARS Baton Rouge, LA

Experimental Design

Mites on Foragers

0

0.02

0.04

0.06

0.08 unselected

Russian

Mit

es

pe

r 1

00

be

es

0

0.02

0.04

0.06 unselected

Russian p = 0.66

p = 0.0156

Infested Cells

0

0.1

0.2

0.3

0.4

Aug -start Aug - end Sept Oct Nov

unselected

Russian

P = 0.002

Pro

po

rtio

n o

f in

fest

ed

se

ale

d c

ells

Mites per 100 bees

0

5

10

15

July Aug Sept Oct Nov

Site-1

unselected

Russian

0

5

10

15

July Aug Sept Oct Nov

Site-2

unselected

Russian

Mit

es

pe

r 1

00

be

es

Mit

es

pe

r 1

00

be

es

Conclusions -The growth of mite populations is positively correlated with proportion of foragers with mites. - The mite population might not be the product

of mite reproduction alone. - Mite resistant lines may not have lower mite populations

How could this happen?

- Parasites and pathogens need dispersal strategies

Photo from the Peace Bee Farmer

Future Directions

Nurse bee Forager

Acknowledgements

• Funded by USDA-Areawide Grant

• Thank you to commercial beekeepers especially Frank Pendell and Randy Verhoek.