The Corpus Allatum and Oogenesis in Rhodnius Prolixus (Stål.)

Abstract

ABSTRACT Mated females lay more eggs than virgin females. They also oviposit earlier in the cycle, and at a higher rate, than virgins. Mated females produce, slightly more than two oocytes per ovariole. Virgin females produce a little more than one oocyte per ovariole. The first wave of oogenesis proceeds at the same rate in mated and virgin females, whereas the second wave is inhibited in virgins. The concentration of yolk protein in the haemolymph remains high for longer in virgins than in mated females. The inhibition of egg production during the second wave of oogenesis in virgins is thus not a consequence of a previous decline in yolk protein titre. Virgin females digest their blood meal more slowly than mated females. The follicular epithelium of an oocyte in the second wave of oogenesis in a virgin shows sparsely scattered intercellular spaces, whereas that of an oocyte from the first wave exhibits the abundant spaces characteristic of a follicle from a mated female. During the time when vitellogenesis is inhibited in virgins there is an accumulation of oocytes in the size range below that of activation. The corpora allata of both mated and virgin females undergo a cycle of increase in size associated with the cycle of oogenesis. There are no differences which can be correlated with the differences in the activities of the ovaries of mated and virgin females. Topical application of farnesyl methyl ether (FME) to decapitated mated females brings about egg development equivalent to that of virgin females. Topical application of FME to virgin females results in the production of the number of eggs characteristic of mated females, but very high doses are necessary to achieve this. These dose levels also result in an increase in rate of oviposition. These effects of high doses of FME are abolished if the virgin females lack their neurosecretory cells. It is concluded that the virgin inhibition of oogenesis results not from a deficiency of allatum hormone, but from the presence of an antigonadotropin released from ovaries which contain mature eggs.