The Nutrimentary Egg Development of the Mite, Varroa jacobsoni (Acari, Arachnida), an Ectoparasite of Honey Bees

Abstract

AbstractThe fine structure of the female gonad of Varroa jacobsoni is described. There are two components: the ovary proper and the so‐called lyrate organ. The ovary is the place where oocytes mature, embedded in a supporting tissue composed of two cell types: somacells 1 and somacells 2. The lyrate organ has a nutrimentary function and is comprised of two components: supporting cells and nutritive tissue. The supporting cells are similar to the somacells 2 in that they contain abundant microtubules. The nutritive tissue is an extensive syncytium. It is connected with the oocytes via intercellular bridges, the nutritive cords. Oocytes and nutritive tissue are thought to have derived from common stem cells. From fine structural evidence it is concluded that ribosomes are one of the most important components to be transported via the nutritive cords into the oocytes. However, an increase in number of mitochondria in the middle‐stage oocytes may also be a consequence of transport of these organelles from the nutritive tissue into the oocytes. Further characteristics make plausible that the interdependences of oocytes and nutritive tissue are comparable to those found in meroistic ovarioles of insects. The somatic components do not seem to be as important as the follicle cells of insects, however. It is assumed that the evolution of a nutrimentary oogenesis speeds up embryogenesis. Thus, the differentiation of the female gonad of Varroa jacobsoni may have facilitated the species' adaptation to a development completed in a short and limited time within the shelter of the covered brood cell of the bee.