Befallsentwicklung von Nosema ceranae im Jahresverlauf in Bienenvölkern (Apis mellifera L.) in Baden-Württemberg und der Einfluss einer gezielten Nosema-Infektion auf Lebensdauer und Flugaktivität der Arbeitsbienen

Publication Type

Master's thesis

Authors

LARUE, A-A.

Year of publication

2011

As part of the Nosema-monitoring EU project Bee Doc the seasonal course of infection with Nosema sp. in Baden-Wuerttemberg was investigated. Thereby, samples from the 15 beekeepers, who have been involved in the monitoring from the winter 10/11 up to June 2011, were examined by light microscopy using a standardized method. During the spring on average the highest numbers of spores per bee (3.9 million spores per bee) were detected in the hives. The spore-infestation decreased over the course of the year, so in June an average value of only 390,000 spores per bee has been detected. The month with the highest prevalence demonstrates April, with 89% tested positive hives. First molecular genetic analysis confirm that in our geographical area under investigation almost solely the new introduced parasite Nosema ceranae appears. Despite this high prevalence and the sometimes very high average spore load per bee (maximum value > 30 million spores per bee) no clinical symptoms were reported by beekeepers. Our results support similar studies from Scandinavia, Switzerland and southern France, bur are in contradiction to publications from southern Spain, which report massive damage caused by Nosema ceranae-infestation of bees.

At further experiments 120 Nosema sp.-bees in small mating nucs were observed for 4 weeks and flight activity and number of surviving bees documented. Additionally, several experimental groups had previously been contaminated with the insecticide thiacloprid, in order to capture any synergistic effects. In spite of a 100% successful infection, the infected bees showed neither a shorter life span nor a lower flight activity compared to the control bees. Finally, synergistic effects of thiacloprid, are noticed neither in lifespan and flight activity nor at the Nosema infestation level, documented 10, 15, 20, 25 and 30 days post infectionem.