Estado sanitario de las colonias de Apis mellifera (Hymenoptera Apidae) de las Islas Balearesimpacto del parásito Varroa destructor (Acari: Varroidae) y efecto de los tratamientos aéreos con Bacillus thuringiensis Subsp. Kurstaki

Abstract

Rapid and substantial losses have been observed in honeybee (Apis mellifera) populations worldwide over the last decade. Honeybees contribute to food security and their extinction would represent a serious biological imbalance. These losses have been attributed to a combination of different potential causes, such as diseases, poor nutrition and frequent applications of insecticides to control pests. The aim of the present thesis was the study of two important factors related to the health status of the honeybee colonies in the Balearic Islands: the mite Varroa destructor and the application of the insecticide B. thuringiensis subsp. kurstaki (Btk). The annual pattern of abundance of Varroa was bimodal, with two peaks, one in spring and other in summer/autumn, being the spring peak always larger. The relationship between Varroa abundance and environmental predictors was examined using Generalized Linear Mixed Models, showing higher Varroa abundance when bee densities increased. Furthermore, Varroa abundance was higher at low temperatures from January to June and lower at high relative humidity periods from July to December. A key novel finding was that low availability of natural flowering resources lead to high levels of infestation of Varroa. The mean infestation of the mite in the Balearic Islands was low (less than 1%), the prevalence detected was between 34.78% during autumn and 44.09% during spring, and more than 80% of the apiaries sampled showed Varroa. The statistical distribution of the number of colonies per apiary with Varroa was fitted to a Poisson distribution, reflecting the endemic epidemiological situation of the parasite in the Balearic Islands. A survey conducted to beekeepers indicated a low-level of professionalization of the apiculture and showed that miticides are frequently wrongly applied. Field assays of the efficacy of miticides revealed that Apiguard (Thymol) was more effective, being Spring the best season to apply the product. Therefore, Thymol could represent an alternative in integrated control strategies against V. destructor, having a low risk of residues and resistance. Finally, our results showed that the aerial treatments of Btk against processionary caterpillar do not affected the brood development of honeybees.