Toluidine blue staining as a rapid measure for initiation of oocyte growthand fertility in Varroa jacobsoni Oud.

A whole mount method was used to determine the moment of activation of oocy te growth in Varroa jacobsoni females. Ovaries of the mites were dissected and stained with toluidine blue. The coloration of the terminal oocyte indi cates the uptake of euplasmatic and/or yolk material and, therefore, the in itiation of the reproductive phase. In phoretic mites from adult bees, no s taining of the ovary could be detected. V. jacobsoni females artificially i ntroduced into Freshly capped brood cells and removed for dissection 6 h la ter already showed clear blue staining of the terminal oocyte. The ovaries of V. jacobsoni females introduced 14 h after capping of the brood cell, ho wever, remained uncolored after incubation in toluidine blue. We conclude t hat, in phoretic mites, oogenesis is arrested at a previtellogenic phase. I mmediately after invasion of the brood cell, reproduction is activated by a n as yet unknown host factor. This factor is present in freshly capped broa d cells but not in brood cells 14 h after capping. Our new method offers ne w possibilities for the exact determination of oocyte growth and, therefore , for the study of V. jacobsoni fertility in different host and parasite po pulations.