2014/6/2
Varroa mite reproductive biology A collaboration with Asian, French and Australian scientists
Zachary Huang Michigan State University East Lansing, Michigan, USA
Varroa destructor Anderson & Trueman (Acari: Varroidae) Adult female : 1.5 x 1.0 mm
ecto-parasitic mite of
the honey bee, Apis http://www.cyberbee.net/ mellifera L.
Reducing Vectoring viruses Inhibit bee’s Adults live emergence wt e.g. DWV, IAPV Immune Response shorter $ protein Is this a female? Male? How many of you have seen a male varroa? Why not? Severe impact on honey bee industry Economic loss on crops
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1. Varroa mite reproduction when Life History of Varroa transferred across species
Phoretic phase
Reproductive cycle
11.5 days on sealed worker larvae 123456789101112131415161718192021222324days egg larva pupa worker
http://www.dpi.vic.gov.au/CA25677D007DC87D/LUbyDesc/Ag1183fig1/$File/AG1183Fig1.jpg Z. Huang photo
Mark with color Transparency Methods • Wait for 6 hrs
Obtain phoretic mites
Transfer mites to cells Back into colony, wait for 6 hrs Incubate at 34ºC, 50% RH Checked daily for wax moth Mark again On day 9 (transfer at day 1), open cells for x x Transparency x x checking mite progenies
Double marked cells: capped within 6 hrs
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Mites were captured & transferred into newly sealed Confining the queen to a Q excluder cage (within 6 hrs) worker brood cells on mite-free recipient frames. Brood was then incubated at 34ºC and 50% relative humidity. Mite Mite extraction Adult eclosion transfer larva prepupa
1 2 3 4 5 6 7 8 9 10 11
123456789101112131415161718192021 days egg larva pupa worker
Map newly capped cells
Mapping brood to obtain newly capped cells Catching mites by hand! (prior to sugar dusting)
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Determining number of offspring per mite Ontogenetic development of the varroa mite
Protonymph Deutonymph
1.1 mm x 1.7 mm
0.5 mm x 0.6 mm
(from Ifantidis 1983)
Varroa from A. mellifera (Korea) and Varroa from A. cerana (Vietnam) and transferred to different hosts (Beijing) transferred to different hosts (Xishuangbanna)
100.0
100.0
80.0 83%
80.0
60.0 60.0
40.0
reproduced 40.0
20.0 17% Percent of mites that 20.0 0% Not tested 87 42 78 133 0.0 0.0 WorkerWorker Drone Drone Worker Worker Drone Drone Percent of mites that Percentreproduced of mites Worker DroneDrone Worker Drone Apis cerana Apis mellifera Apis cerana Apis mellifera Korea haplotype Varroa from mellifera can reproduce on both species Vietnam haplotype Varroa from cerana can reproduce and on both castes: % mites reproduced almost identical only on drones of cerana. Even on mellifera drone it was low.
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2. Large cell size reduces varroa reproduction 2. Large cell size reduces varroa reproduction Varroa from mellifera transferred to worker larvae That were reared in worker or drone cells 2.0 2000 100
1.5 75 Workers reared in drone cells: Workers reared in 1.0 50 drone cells
0.5 25 Workers reared in worker cells 2.5 2001 100 2.0 75 1.5 50 1.0 Percent of reproductive mites Mean number of female offspring 25 0.5
Figure 1. Mean number of female offspring and percent of mites that reproduced on worker brood reared in different cell types. Experiments were conducted in 2000 and 2001 in Beijing, China. Varroa reproduced better in worker cells, suggesting large cells can inhibit reproduction. It is not cleare if workers are different (e.g. more queen-like), or due to actual cell size difference.
3. Chemical mimicry of mites 3. Chemical mimicry of mites to different species of honey bees • Transfer of mites from Ac brood – Ac brood (MCC) Previous studies have shown that the varroa mites – Am brood (MCM) can mimic the host cuticular hydrocarbons, perhaps enabling them to escape the hygienic • Transfer mites from an Am brood behavior of the host honey bees. – Am brood (MMM) – Ac brood (MMC) Martin C, Salvy M, Provost E, Bagnères A, Roux M, Crauser D, Clement J, Le Conte Y. 2001 Variations in chemical mimicry by the After 8 days, the mother mite, their daughters and the host ectoparasitic mite Varroa jacobsoni according to the developmental stage of the host honey-bee Apis mellifera. Insect Biochem Mol Biol. pupae were extracted from cells and washed in hexane. 31: 365-79. The chemical signatures of both Apis puape and their Varroa parasites were determined by GC/MS.
Z. Huang photo Z. Huang photo
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MMM: mother-mite, mellifera to mellifera, MCM: mother-mite, cerana to mellifera MMC: mother-mite, mellifera to cerana, DCC: daughter, cerana to cerana BCM = A. mellifera hosting Ac mite (K3), BMC = A. cerana hosting Am mite (K2) 3. Chemical mimicry of mites to BMM = A. melliferea hosting Am mite, BCC = A. cerana hosting Ac mtie different species of honey bees
Summary:
1.Regardless of previous hosts (cerana or mellifera), mites transferred to A. cerana are more similar to A. cerana pupae profile DMM6 1). MMM=MCM, MMC=MCC 2). BMC=BCC, BCM=BMM 2.Regardless of previous hosts (cerana or mellifera), mites transferred 3). D not better than M to A. mellifera are more similar to A. mellifera pupae 4). A few perfect mimickers? Mites are able to mimic their hosts, even when the hosts are of different species! Remarkable ability to use chemical camouflage.
Component 1 – 24.1% Z. Huang photo
4. Do phoretic mites prefer nurse in a colony setting? Materials and Methods Although mite biology has been well 4. Preference for phoretic hosts studied, we still do not know: Triple cohort colonies: Whether Varroa mites prefer nurse bees over 500 of each: foragers, nurse bees and newly emerged bees older and younger bees in colonies. + a frame of honey, a frame with pollen, and a queen
-- Prior studies used petri-dishes/caged bees
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Mite source: ~200 mites introduced into the triple cohort colony Sugar dusting adult bees 24 hrs later, workers in each group recovered with forceps
Killed in alcohol and mites recovered
Sugar dusting
Statistical analysis 5. Why phoretic mites prefer nurse in a colony setting? Hosts # of bees # of mites
Foragers 394 22 Nurses 425 56 Several possibilities: 1. Foragers should be avoided due to higher risk Summary Table for Row s, Columns 2. Nurses are close to larvae, more opportunity to Num. Mis s ing 0 jump in Observed Frequencies for Row s, Columns DF 1 Column 1 Column 2 Totals Chi Square 13.679 3. Nurses may have different nutrition, resulting in Row 1 372 22 394 Chi Square P-Value .0002 higher fitness? Row 2 369 56 425 G-Squared 14.168 G-Squared P-Value .0002 Totals 741 78 819 Contingency Coef. .128 We tested hypothesis #3: do mites which had Phi .129 Cty. Cor. Chi Square 12.813 previously fed on nurses show higher fitness? StatView outputs Cty . Cor. P-V alue .0003 Fisher's Exact P-Value .0002 Z. Huang photo
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9 days later, mite reproductive success were evaluated Experiment 5
All mites harvested from pupae Mites let to feed on caged bees (three types of hosts) for 3 days
5. Effect of host type on mite reproduction: Day-old bees: consistently give mites lower fitness 5. Effect of host type on mite reproduction: Foragers: quite constant Nurses: variable Day-old Nurses Foragers
Day-old Nurses Foragers
4.5 B 4.5 B 4 4
3.5 B B A 3.5 AB AB 3 A 3 2.5 AB 2.5 A 2 A 2 A 1.5 1.5 1 1 17 23 10 13 Age of nurses 10 13 17 23 Age of nurses .5 .5
Number of female offspringof femalemother Number per 0 offspringof femalemother Number per 0 1 2 3 4 3 4 1 2 Colony (Replicate) Colony (Replicate)
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There is a significant negative relationship between the age Summary of the phoretic hosts and mite fecundity
4.50 4. Do Varroa mites prefer nurse bees over
2 older and younger bees? 4.00 R = 0.986, P<0.007 -- Yes, not only in petri dishes or caged 3.50 bees, but also in more natural colony settings. 3.00
Mite Fecundity 5. Is mite reproduction affected by 2.50 feeding on different phoretic hosts? -- Yes, and there is an inverse relationship 10 12 14 16 18 20 22 24 between age of nurses and mite fecundity.
Age (days) of the nurses
Conclusions 1. Mite reproductions affected by many factors: Supported by grants from USDA-SCP, USDA-PMAP, the Greeen Program at MSU ChinaNSF. 1. Pupal host type [email protected] 2. Cell size 3. Phoretic host type
2. Mites clearly prefer nurses, perhaps mainly due to a fitness gain.
3. Mites have remarkable ability to mimic their host cuticular hydrocarbons.
Thank you!
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