Efficacy of thymol nanoemulsion against Varroa destructor mites infesting Apis mellifera colonies under the stress of abiotic factors in Egypt

Abstract

ABSTRACT Varroa destructor is a serious pest threats honey bees health worldwide. This study aims to evaluate the effect of thymol nanoemulsion against Varroa. The experiment comprised four colony groups; control, thymol emulsion (Th) 100 ppm, thymol nanoemulsion (NTh) 50, and NTh 25 ppm. NTh 25 ppm was the most potent with insignificant difference and no correlation with temperature, followed by Th 100 ppm, NTh 50 ppm and control groups with fallen Varroa of 70.45%, 67.59%, 60.08% and 51.49%, respectively. NTh 25 ppm group exhibited moderate candy consumption (45%) when compared to Th 100 ppm (47.35%) and control (52.09%) groups with insignificant differences. The pollen consumption was significantly the highest in the NTh 25 ppm group (41.59%) compared with the NTh 50 ppm (36.73%), Th 100 ppm (33.99%) and control (33.69%) groups. NTh 50 ppm has the lowest fallen Varroa and candy consumption percentages. Thymol nanoparticle size (17.6 nm), high zeta potential (-20.1 mv) and low diversity index (0.383) revealed the thymol nanoemulsion stability. So, NTh 25 ppm may decline residues and thymol sensitivity to temperature and increase affordability by one-quarter. Moreover, pollen consumption increase in NTh 25 ppm may enhance colony immunity.