Microcalorimetric and Microbiological in Vitro Investigations on the Acaricidal, Insecticidal, and Antimicrobial Effects of Propolis

The ideal conditions in the beehive interior expose the colony to several parasites, pests, and pathogens. Moreover, the high density of individuals in honeybee colonies facilitates the transmission of parasites and pathogens in the hive. Presently, beekeeping with the western honeybee Apis mellifera L. is endangered by the parasitic mite Varroa destructor (Anderson and Trueman). In addition, pests such as Galleria mellonella, and bacterial, fungal, and viral pathogens also remain a common problem. The energy and nutritional demands of the parasitic lifestyle of Varroa mites have been demonstrated in this thesis, for the first time, through mite starvation and calorimetric experiments. The mites suck up to 28 % of the non-replenishable reserve food of the capped brood that otherwise would have been consumed by the pupa during metamorphosis. This in turn leads to the emergence of crippled bees, and can be aggravated by viral, bacterial, and fungal infections. The antivarroa action of propolis (bee glue) has been investigated for the first time calorimetrically, respirometrically, and using the Petridish bioassay method. Propolis samples collected from different geographic origins showed Varroa narcotizing and varroacidal effects. The length of narcosis and mortality rate of mites depended on the solvent of extraction (70 % or 40 % ethanol, or water), concentration of propolis, and contact time. Propolis extracted in 70 % ethanol has been found to be highly toxic, resulting in the death of 80 % to 100 % mites regardless of the contact time and concentration of propolis. The treatment with 40 % ethanol-extracted propolis was less effective, followed by the water extracted propolis. The insecticidal action of propolis has been demonstrated by dipping the different larval stages of the greater wax moth Galleria mellonella in ethanol-extracted propolis for 30 s. The treatment with propolis narcotized the larvae, and reduced their metabolic rates remarkably. Higher concentrations of propolis such as 10 % (w/v) caused larval mortality, whereas lower ones (1 % and 2 %) displayed insect growth regulator actions by shortening the length of pupal metamorphosis. A 4 % w/v propolis resulted in the abortion of metamorphosis. The antimicrobial actions of different extracts of propolis from various geographic origins were compared by using parameters such as the minimal inhibitory concentrations (MIC), minimal bactericidal concentrations (MBC), diameter of the inhibition zone, and several parameters of the heat production rate vs. time (p-t) curves. For all propolis samples tested, the strength of antimicrobial activity decreased in the order of ethanol-extracted propolis (EEP), propolis volatiles (PV), and water-extracted propolis (WEP). For some propolis samples, however, there was no remarkable difference in the strength of antimicrobial activities between EEP and PV. The extraction of propolis with ethanol procures all water soluble, ethanol soluble, and the volatile components of propolis making EEP superior to the other two extracts qualitatively and/or quantitatively. The Gram positive bacteria were more sensitive to propolis treatments than the Gram negative ones and the fungi. The lower sensitivity of Gram negative bacteria can be accounted for by the impermeability of their outer membrane to antibacterial agents. Filamentous fungi were less sensitive to propolis treatment than yeasts, the latter showing higher diameters of inhibition zones especially at higher propolis concentrations. The antimicrobial, insecticidal, and acaricidal actions of propolis illustrated here show that propolis can be used in the control of parasites, pests and pathogens of the honeybees.