Effect of organic and inorganic zinc supplementation on the development of mandibular glands in Apis mellifera

We investigated the effects of organic and inorganic zinc (Zn) supplementation on the morphology of mandibular glands in Apis mellifera L.. We randomly assigned 28 beehives to seven treatment groups (four beehives in each group) as follows: control (no Zn) and Zn organic or inorganic supplementation (25, 50, and 75 ppm organic or inorganic Zn, respectively). The inorganic source was Zn sulfate monohydrate (37% Zn) and the organic source was Zn-methionine (16% Zn), which were diluted in sugar syrup 1:1 (50% water and 50% sugar) and provided to the honey bees for 36 days. The morphology of the mandibular glands collected from 6-day-old nurse honey bees from each group was analysed after sectioning and visualizing the sections under a microscope. The results were compared using analysis of variance followed by Tukey's test. The area of the mandibular glands increased significantly in the treatments containing the organic Zn source and was higher in the 75 ppm treatment. The results from the inorganic Zn sources of 25 and 50 ppm were similar to those of the control; however, the 75 ppm treatment showed the worst glands development. Therefore, organic Zn supplementation in the feeding of honey bees, in the concentrations used in this study, positively modulated development of the mandibular glands.