Current and Future Management Strategies for Varroa Mites

Ramesh Sagili [email protected]

Overview of Honey Bee Research Projects at OSU 

Honey Bee Nutrition



Nosema ceranae



Effects of Pesticides



Applied studies on Varroa control

Resting Worker Bees



How many of you lost significant number of colonies past winter?



What factor or factors do you think was/were responsible for your colonies' demise?



How many of you monitor Varroa levels in your colonies?



How many of you use Varroa mite treatments?



How many of you think Varroa mite is a problem or responsible for your colony loss?

Varroa mite life cycle

First egg after 70 hours and subsequent eggs at 30 hour intervals

(DM Caron)

Female

Male

PMS (parasitic mite syndrome) Virus transmission: DWV, IAPV, KBV, CBPV, BQCV Before arrival of Varroa, viruses were considered a minor problem. Varroa is responsible for direct injection of virus particles.

PMS

Varroa 

History of Varroa mite



Why Varroa is a greater menace of European honey bee but not for the Asian honey bee?



Host-parasite relationship



Natural selection is a long process to get the resistance or tolerance



In Apis cerana, Varroa is unable to reproduce in worker brood

Bee Informed Partnership Survey 2012-13 

Beekeepers who reported using treatment for Varroa lost 26% fewer colonies than those that did not use a mite treatment.

Reasons for Colony Losses 2010

2011



Queen failure (30%)



Queen failure (29%)



Mites (24%)



Starvation (21%)



Starvation (17%)



Mites (16%)



CCD (13%)



CCD (12%)

Madras, OR Sampling Results: Varroa mite levels

1.2

Percent Infestation

1.0

0.8

0.6

0.4

0.2

0.0

First week of July

Last week of July

Time

Varroa IPM In Honey Bee Colonies

IPM Combination of various available control methods both chemical and nonchemical.

Periodic monitoring of mite levels

Varroa mite economic threshold levels 

ET is not universal



ET depends on: geographic location, level of colony resistance to Varroa etc.



ET range of 20-80 mites/day (sticky board data) is suggested in the existing literature



ET in terms of percentages (Alcohol wash): Spring / summer: > 1% Fall: > 3% Late fall / winter: > 10%

Honey bee and Varroa mite population dynamics

Scientificbeekeeping.com

Of course don’t get the mite loads to this level !!



Varroa mite treatments should not be calendar based but based on realistic mite population levels.



Early brood rearing means early mite control strategies to be implemented.

Treatments  Synthetics (Organophosphates, Synthetic pyrethroids)  Organic

chemicals

Amitraz (Apivar) 

Contact miticide



2 strips per brood chamber



Degrades relatively faster (3-4 weeks)

Some important considerations when using Apivar 

Results can be variable depending on factors such as: Dose and placement of strips.



Appears to decrease mite populations gradually.



Using in spring may be the best option.



Risk of resistance development....resistance development can be delayed following removal directions and rotating with other available options.

Apiguard Thymol (slow release gel) Temperature dependent (60-100º F) Also active against tracheal mites

Treatment

% age decrease in brood (uncapped + capped)

Mite mortality

50 gm on top with spacer

18

77

50 gm in middle with spacer

26

86

50 gm on top without spacer

26

73

50 gm in middle without spacer

39

80

25 gm on top with spacer

26

75

25 gm in middle with spacer

22

84

25 gm on top without spacer

26

71

25 gm in middle without spacer

37

82

No Queen loss observed in any of the experimental hives

MAQS and Hopguard Mite-Away Quick Strips (MAQS)

HopGuard

Mite-Away Quick Strips (MAQS)      



Formic acid (46.7%) Recommended dose: 2 strips per treatment Treatment period: 7 days Temperature range: 50-92ºF Colony size: colony cluster covering a minimum of 6 brood frames Excessive temperatures (>95ºF can cause excessive brood mortality and absconding) Kills male and female mites in capped cells (advantage: mite reproduction is restricted) (is there a problem in pupal development?)

Infestation level after treatment (percentage of mites)

Efficacy of MAQS, Apiguard and Hopguard 14

12

10

8

6

4

2

0 MAQS

Apiguard

Hopguard

Treatments

Control

Oxalic Acid 3% Oxalic acid sprayed 3-4 ml per comb side killed 98% mites. Ideal when colonies are broodless (Nov or Dec). Not registered for use in The U.S.A.

Cultural Methods (Non chemical treatments) 

Drone comb traps



Screened bottom board



Powdered sugar dusting

Other strategies to reduce mite reproduction 

Small cell foundation -may be we will increase additional cycle of brood providing mites more opportunity to breed -also may be putting selective pressure on mites to develop faster (reduce life cycle)



Creating intermittent brood less periods

Biological Control 

Predatory Mite: Stratiolaelaps scimitus



Stratiolaelaps scimitus is a soil dwelling predatory mite



Currently used for controlling Fungus gnats and thrips.

10 Treatment Colonies 10 Control Colonies

Control Colony

Predatory Mite Treatment Colony

Mite with no damage

Mites with damaged appendages

Future Strategies for Varroa Control  RNAi

(interference)



Gene knockdown or gene silencing and stop protein expression (done by synthesizing a doublestranded RNA).



DNA…….mRNA…….rRNA (directs the translation of mRNA in to proteins).



dsRNA impairs translation of viral proteins-reduces viral replication.



May be a therapeutic alternative in the future.

Questions???