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Institut für Phytomedizin

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Browsing Institut für Phytomedizin by Person "Al-Attal, Yehya Zaki Khalid"

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    The host parasite relation of the parasitic mite Varroa destructor (Anderson and Trueman) and the honeybee races A. m. syriaca (Skorikov) and A. m. carnica (Pollmann) in Jordan.
    (2006) Al-Attal, Yehya Zaki Khalid; Zebitz, Claus P. W.
    Since the honeybee mite Varroa destructor (Anderson and Trueman) succeeded to parasitize the Western honeybee Apis mellifera L. and accept this species as a new host it became the most serious threat to Apiculture worldwide. The very few stable relations between Varroa mites and the new host are either associated with honeybees of African origin, or with tropical and sub-tropical climates. This balanced relations seems to be due to reduced fertility of the female mites in worker brood cells, a shorter post-capping period of the worker brood and a set of highly differentiated active defense traits of the host bees. In this work I investigated several aspects of the host parasite relation between the honeybee and the Varroa mites in Jordan. The endemic honeybee race of Jordan is A. m. syriaca Skorikov, which join African and European bee traits. The Jordanian beekeepers use this ?local? bee as well as its hybrids with imported European bees. Therefore, Jordan provides the possibility to prove the influence of different honeybee races and different climatic conditions on this host-parasite system. For a better direct comparison, I evaluated the host-parasite relation of two honeybee races at the same study site: the ?local? honeybee (A. m. syriaca) and the imported ?carnica? honeybee (A.m. carnica Pollmann), which is susceptible to Varroa infestation under Central Europe conditions.To assess the current status of Varroa mite in Jordan, we surveyed the infestation rates of in capped brood cells and on adult worker bees in 180 honeybee colonies at six locations. All colonies were kept untreated for at least 8 month. The results revealed high infestation rates, which exceed, in part, the thresholds for colony damages. No significant differences between honeybee races or climatic condition were visible. The population dynamics of the host and its parasite represents the most important parameter of the honeybee-Varroa relation and was described in the ?local? and the ?carnica? (imported from Hohenheim) honeybees at Baqa (dry Mediterranean climate) and Yadodeh (wet Mediterranean climate) for a one-year period. In all colonies the number of adult bees and brood cells were evaluated every three weeks by the ?Liebefeld? method. During all evaluations, samples of adult bees and capped brood of all colonies were analyzed to determine Varroa infestation rates. The population dynamics of the honeybee colonies revealed a significantly higher population density of the ?local? honeybee race compared to the ?carnica? colonies. The average number of adult worker bees was 8,368 ± 2,724 in the ?local? colonies and 6,447 ± 2,338 in the ?carnica? colonies, while the average number of capped worker brood cells was 9,164 ± 3,336 in the ?local? and 7,628 ± 3,166 in the ?carnica? colonies. Compared to colonies in Central Europe, my results indicate a surprisingly shorter life span of adult worker bees. The corresponding population dynamics of Varroa mites revealed an exponential growth phase till the maximum infestation and a decreasing phase until the beginning of the next season. The maximum Varroa population density ranged between 2,614 ± 2,190 mites in the ?carnica? colonies and 4,397 ± 2,746 mites in the ?local? colonies. Using an exponential function, growth rate = eb, the average exponential growth rate of Varroa population per three weeks interval ranged between 1.33 and 1.46 and was significantly different between both locations. The subsequent decrease in the mite population was two folds higher than the decrease in the effective bee population (adult bees plus capped worker brood cells together). Therefore, a higher mortality rate of the parasites or its host activity must contribute to the observed drastic decrease of the Varroa population. No significant race-specific differences in the infestation rates could be observed. However, the mortality rate was higher in the ?carnica? colonies (? 40%) compared the local colonies (? 10%). This indicates a general higher fitness of the ?local? colonies independent from Varroa infestation rates. As a threshold for the survival of honeybee colonies, maximum infestation rates of 20% in adult worker bees and 40% in capped worker brood were determined. The evaluated resistance mechanisms, which are considered to contribute to stable host-parasite relations, did not reveal any pre-adaptation of the ?local? honeybee to Varroa mite. Neither in the fertility of female mites nor in the reproductive rate significant differences between the local and the ?carnica? honey bee race could be detected. The post-capping period of the worker brood was nearly the same in both bee races and it corresponds to data from Central Europe. Also no significant difference could be revealed in the daily mite mortality between both races, which ranged between 0.8% and 1.5% of the total mite population in the colonies. Nevertheless, in few individual ?local? colonies, the mite mortality comprises a surprisingly high percentage of the total estimated number of the phoretic mites within the colonies. By RFLP of the CO-I unit, only the V. destructor Korean haplotype was detected in all examined mite samples from Jordan. Additionally, mite genotyping based on the sequences of two genetic markers shows very low genetic variability among different mite populations, which confirm recent publications and makes the hypothesis that differences in mite virulence could be responsible for a stable host parasite relationship, less probable. Conclusions ? The ?local? honeybee of Jordan is not more resistant to Varrosis compared to the susceptible European honeybee races. ? The Mediterranean climate has no significant inhibition effect on Varroa population dynamics. ? Varroa infested ?local? honey bee colonies revealed a significant higher survival rate than imported ?carnica? colonies under the same conditions. ? Variation in the mite infectivity between different V. destructor population is less probable.