Fenologia da Nosemose tipo C (Nosema ceranae) em colônias de abelha ibérica (Apis mellifera iberiensis): relação com a força da colônia

Abstract

The honeybee (Apis mellifera L.) is an important source of ecosystems balance since it promotes the pollination of several plant species. However, in the last decades, honeybees have suffered a dramatic decline due to several factors. Diseases, such as Nosemosis type C (Nosema ceranae) and Varroosis (Varroa destructor), have been widely spread due to commercialization of honeybees. Thus, the main goal of this work was to evaluate the relationship between N. ceranae and colony strength, including the evaluation of environmental conditions. Additionally, the colonies were characterized molecularly using mitochodrial DNA as a molecular marker. The variables, colony strength, number of frames with brood, brood solidness of central frame, infestation rate of V. destructor and collection of honey bees for the Nosemosis analysis was performed every two months between february to october 2018. Parameters such as colony weight and environmental conditions (wind velocity, temperature, precipitation, and relative air humidity), as well as, monitoring of internal conditions (temperature and humidity) were recorded daily through a weather station linked to the automatic balances and hydrothermal sensors, respectively. Additionally, the annual honey production of the colonies under study was estimated. The correlation between colony strength and Nosemosis infection rate was estimated with a path analysis using a statistical program (GENES). The results showed that the colonies studied were 8 colonies of the lineage A and 4 of the lineage M. Regarding colony strength, it was observed that, in the summer, the number of frames covered with adult bees reached an average of 15 frames per colony, and in the winter that number decreased to 7. The same pattern was observed for the variables number of frames with brood and brood solidness. The variable weights showed a considerable increase from April to August (active season), ended up with an average of 37 kg of honey per hive. The internal colony monitorization showed a higher stability pattern for the temperature and humidity, from April to August, which coincides with the active season. Regarding the diseases, no pattern of V. destructor infestation was observed, however, high rates of varroosis occurred even after treatment for some colonies (6 of 12). The infection rate of Nosemosis type C showed a seasonal pattern, with a peak in early spring (80%) and a smaller one in autumn (52%). The results of the track analysis explained only 19% of the N. ceranae infection rate, thus the colony strength variables, as well as, varroosis did not demonstrate high associations with the N. ceranae infection rate. This study was helpful to understand and determine the infection levels of N. ceranae on the colonies in the northeast of Portugal, contributing to a better knowledge of the microsporidium N. ceranae behaviour over the year.