Regulation of female reproduction in mites: a unifying model for the Acari.

It is well established in the literature that circulating high levels of juvenile hormone (JH) are responsible for the initiation of vitellogenesis and female reproduction in most insects studied so far. Exceptions include some Diptera, Lepidoptera and Hymenoptera. The current view is that JH also regulates yolk protein (vitellogenin, Vg) synthesis and female reproduction in mites. However, there is no published evidence that mites have the common insect JHs at any stage of their development. Also, research on the effects of exogenous applications of JH and JH analogs on the reproduction of mites is contradictory. Significant information is available on the life history of mite reproduction, and new information has become available on mite storage proteins including Vg. Although initial studies suggested that ticks may respond to exogenously applied juvenile hormone or anti-JHs, current research shows that ticks cannot synthesize the common insect JHs and have no detectable levels of these hormones in their hemolymph during female reproduction. In ticks, it appears that ecdysteroids, and not JH, regulate expression of the Vg gene and the synthesis and release of Vg protein into the hemolymph. In fact within the Arthropoda, JH has been found only in insects. Methyl farnesoate and not JH regulates Vg synthesis in the Crustacea, the sister group to the insects. Based on this evidence, a new working hypothesis is proposed, i.e., that ecdysteroids and not the JHs regulate vitellogenesis in the Acari including both ticks and mites. To the present, the role of neuropeptides in the regulation of female reproduction in mites is not known.