Comparison of the reproductive ability of varroa mites in worker and drone brood of Africanized Honey Bees

Transcription

1 Comparison of the reproductive ability of varroa mites in worker and drone brood of Africanized Honey Bees Rafael A. Calderón F. Tropical Beekeeping Research Center (CINAT) Universidad Nacional, Costa Rica Apimondia Montpellier France 1

2 I. Introduction - Varroa destructor is an ectoparasite of serious economic importance for beekeeping - Severe colony mortality is reported in EHB colonies in Europe, Asia and North America Apimondia Montpellier France 2

3 - In order to reproduce varroa females enter worker or drone brood shortly before the cell is sealed - The reproduction of varroa mites is a significant factor determining its virulence and has a major impact on the persistence of both host and parasite Apimondia Montpellier France 3

4 - Because varroa populations increase when brood is present - It would be expected that in tropical climates, where brood rearing takes place year-round - The effect of varroa would be even more devastating Apimondia Montpellier France 4

5 - However, reports for AHB in Brazil indicate tolerant / resistant varroa - Colony losses are not reported for AHB in Brazil - The mechanisms for this apparent resistance or tolerance are not well understood Apimondia Montpellier France 5

6 However, regional differences in: - Season length - Weather conditions - Bee and mite genotypes - Make it difficult to characterize the mite impact on AHB over a widespread area Apimondia Montpellier France 6

7 Varroa situation in Costa Rica / Central America - V. destructor was detected in Costa Rica = September It was confirmed as a Korean haplotype - As a consequence of varroa incidence in the apiaries - Beekeepers reported loss of colonies, decrease honey production Apimondia Montpellier France 7

8 Treatment of the AHB colonies in Costa Rica - Because the beekeepers are afraid of reduced honey yields due to high infestation rates - A high percentage of beekeepers treat their colonies annually - Synthetic and natural acaricides are used for mite control - Percentage beekeepers who do not use acaricides is less than 10% Apimondia Montpellier France 8

9 High varroa infestation levels in AHB - Costa Rica - Rates of 191 fallen mites per day - A total of 8000 mites per colony - Occurrence of Deformed wing virus and Kashmir virus - Revealed that varroa serious problem on AHB in Costa Rica Apimondia Montpellier France 9

10 Varroa reproduction on AHB in Central America - Scientific information on mite reproduction AHB in Central American conditions is scarce Apimondia Montpellier France 10

11 Aim of this research - Because scientific information is not available - Due to climate and race have an effect on varroa populations - Aim of this research get knowledge about relationship between varroa and AHB in Central American conditions Apimondia Montpellier France 11

12 Main objective: study the reproductive ability V. destructor in worker and drone brood on AHB Apimondia Montpellier France 12

13 Hypothesis: - Due to the preference of mites to invade drone brood to reproduce, we hypothesized that a high proportion of the mite reproduction should occur in drone cells of AHB - To test this hypothesis, we compare the reproductive rate of V. destructor in worker and drone cells of AHB colonies under tropical conditions Apimondia Montpellier France 13

14 II. Materials and Methods Study site: - The study was carried out at Bee Research Institute (CINAT), Universidad Nacional, Heredia - Costa Rica - It was conducted from January to August - January - April = dry months - May - August = rainy months Apimondia Montpellier France 14

15 Heredia is located in the Central Valley of Costa Rica. North=Nicaragua; South=Panama; east= Caribbean sea; West=Pacific ocean Apimondia Montpellier France 15

16 - Experimental apiary was formed for 10 AHB colonies - Experimental colonies at CINAT = Apimondia Montpellier France 16

17 Bee species - AHB: Africanized honey bees - Highly defensive bees - Killer bees - In which both worker brood (WB) and drone brood (DB) were reared Apimondia Montpellier France 17

18 Experimental design Reproductive ability of V. destructor in worker brood - Mite reproduction in worker brood was analyzed approximately 10 days after cell sealing - The number of offspring was determined using a stereoscope microscope - Offspring were classified as egg-larva, protonymph (mob / imm), deutonymphs (mob / imm), male and female adults Apimondia Montpellier France 18

19 Reproductive ability of V. destructor in drone brood - Reproduction of same mother mite in worker cell was compared with what they produced subsequent cycle in drone brood - After determining the number, developmental stage and sex of the offspring in worker cells - The same foundress female mite was immediately transferred into uninfested drone cell Apimondia Montpellier France 19

20 - We assured to have drone cells prepare mite transfer from worker brood - This method allows the possibility to compare the reproductive ability of varroa mites in both worker and drone brood cells Apimondia Montpellier France 20

21 - To introduce the female mite into the drone cell a small cut was made in the border of the cell - letting mite in = using a paintbrush Apimondia Montpellier France 21

22 - Frames were replaced into the colony - After 10 days the cells were opened and checked - Mites (mature / immature) were identified and counted Apimondia Montpellier France 22

23 Different mite stages in worker and drone brood cell Apimondia Montpellier France 23

24 Adult male Apimondia Montpellier France 24

25 New daughter and deutonymph Apimondia Montpellier France 25

26 Adult female mite Apimondia Montpellier France 26

27 Variables measured for foundress female mites - Fertility: production of offspring - Production viable female mite:potentially reproductive offspring - Fecundity: number of progeny - Production of only inmature offspring - Production of only female or only male: one adult sex - No reproduction at all: mites producing no offspring Apimondia Montpellier France 27

28 Viable females in drone brood - To estimate the total viable female offspring in drone brood - The deutonymphs (immobile) were considered - Since under natural conditions the drone cell remains capped hours more - It is enough time for the stage to reach adulthood Apimondia Montpellier France 28

29 III. Results Apimondia Montpellier France 29

30 1- Reproductive rate V. destructor AHB 1.1 Varroa fertility = mites producing offspring - Worker brood= 76.5%; Drone brood= 79.3% - No significant differences were found between the groups (X 2 = 0.78, P= 0.37, n= 370) Apimondia Montpellier France 30

31 1.2 Fertile (viables) females offspring (1 F/ 1 M) - There was a clear difference in the percentage of mother mites producing viable female offspring in worker and drone brood - Being drone brood more suitable for mite reproduction - WB=13.8%; DB= 38.1%, (X 2 = 55.4, P<0.01, n= 370) Apimondia Montpellier France 31

32 - A total of 68 and 287 viable females offspring were produced from 370 worker and drone cells, respectively - More than 23.0% of the foundress mites that produced immature offspring or only an adult sex in worker brood - Produced viable females when they were transferred to drone brood Apimondia Montpellier France 32

33 1.3 Number offspring produced in the groups - Maximum offspring Worker brood = 6 - Frequent # eggs laid Worker brood = Maximum offspring Drone brood = 7 - Frequent # eggs laid Drone brood = The average fecundity of reproducing mites was 2.9 ± 1.4 (n= 290) and 3.8 ± 1.6 (n= 293) descendants per foundress in worker and drone brood, respectively Apimondia Montpellier France 33

34 1.4 Varroa mites that do not reproduce at all - Mites do no produce offspring at all - Worker brood = 23.5 %; Drone brood = 20.7 % - Not significant different X 2 = 0.78, P= 0.37 Apimondia Montpellier France 34

35 1.5 Varroa mites produce only immature offspring - A significant difference was found in the percentage of mothers producing immature offspring in worker and drone brood - Worker brood= 40.6%; Drone brood= 13.2% (X 2 = 69.0 P< 0.01) Apimondia Montpellier France 35

36 1.6 Varroa mites only produced daughter offspring - A greater proportion of mites produced only a female offspring in drone brood cells - Worker brood= 7.2%; Drone brood= 15.2% Apimondia Montpellier France 36

37 1.7 Varroa mites only produced male offspring - The presence of only male in the cells was not different between the groups (CHI-Test: X 2 = 0.74, P= 0.40) - Worker brood = 14.9%; Drone brood = 12.8% Apimondia Montpellier France 37

38 Summary:mites produce offspring (strict fertility) Characteristic WB (%) DB (%) Produce offspring Not offspring Total = Apimondia Montpellier France 38

39 Summary: varroa reproduction parameters Parameter WB (%) DB (%) Viable daughter Immature offspring Only daughter Only male Total = Apimondia Montpellier France 39

40 No reproducing mites in worker cells - A total of 85 foundress mites did not reproduce worker cells - The reproductive behaviour of the majority of these nonreproducing mites became different between subsequent reproductive cycle in drone brood % of the non-reproducing mites produced offspring when were transferred to drone brood Apimondia Montpellier France 40

41 Worker to drone brood - Of the mites that reproduced in drone brood, 36.5% produced viable females offspring - The production of offspring was influenced by brood-type - Only 25.9% of the mites remained the same with no reproduction between transfers Apimondia Montpellier France 41

42 Key factors related with mite infestation increase - The observed mite infestation increases AHB suggests 1- Number varroa reproductive cycles in worker brood 2- The mite reproductive success in drone brood cells 3- Amount and length period drone brood is in the colonies Could be Key factors related with mite population growth on AHB in Costa Rica Apimondia Montpellier France 42

43 4. Conclusions - Mite fertility was similar between worker and drone brood. - Nevertheless, a significant difference in the number of foundress mites producing viable female offspring and immature offspring was found, being drone brood more suitable for mite reproduction. Apimondia Montpellier France 43

44 - The number of eggs and viable females produced per foundress mites was higher in drone brood compared to worker brood. - Furthermore, a high percentage of the non-reproducing mites in worker brood produce offspring when they were transferred to drone brood. - Brood type has an influence in the reproductive success of varroa mites in Africanized bees. Apimondia Montpellier France 44

45 5. References. Calderon R A, Sommeijer M J, De Ruijter A, Van Veen J W (2003) The reproductive ability of Varroa destructor in worker brood of Africanized and hybrid honey bees in Costa Rica. Journal of Apicultural Research 42: Calderón R. A.; L. G. Zamora; J. W. van Veen (2007) The reproductive rate of Varroa destructor in drone brood of Africanized honey bees. Journal of Apicultural Research 46(3): Calderón R. A.; L. G. Zamora; J. W. van Veen; M. V. Quesada (2007) A comparison of the reproductive ability of Varroa destructor (Mesostigmata: Varroidae) in worker and drone brood of Africanized honey bees (Apis mellifera). Experimental and Applied Acarology 43(1): Apimondia Montpellier France 45

46 6. Recommendations future studies - Amount and length period drone brood colonies - Mite population build up in drone free-colonies - Direct observation of varroa activity inside worker and drone artificial cells Apimondia Montpellier France 46

47 7. Acknowledgements - The financial support to take part in APIMONDIA 2009/ Montpellier-France was provided by: Scholarship Department, Universidad Nacional of Costa Rica Science and Technology Ministry of Costa Rica = MICIT Science and Technology Administration of Costa Rica = CONICIT Apimondia Montpellier France 47