Spermatozoa of Lepidoptera

II. Sperm behavior in the artificial insemination between Bombyx and Lymantria.

Abstract

In the previous paper (Ômura, 1939) it was reported that, so far as the Spermato-prostatic reaction is concerned, there occurs no remarkable difference in the behavior of the spermatozoa nor, as well, in the nature of the prostatic secretion, between Bombyx mori and Lymantria dispar. That fact inspired the present study, the main object of which is to learn the fate of Lymantrian spermatozoa artificially inseminated into the bursa copulatrix of the female moth of Bombyx, in hope of making some contribution to the problems on the isolation of species and to the knowledge of specific difference of spermatozoa.
First, as a control experiment, Bombycian spermatozoa taken from the vesiculae seminales and ampullae ductuum deferentium of virgin male moths were activated by adding their own prostatic secretion, and then they were inseminated artificially into the bursae copulatrices of female Bombycian moths (cf. Omura, 1936). All of the experimented females successfully received the semen in their bursae copulatrices and laid many fertilized eggs. In their receptacula seminium, as to be expected, there were found abundant spermatozoa (Table 1). Next, the Bombycian spermatozoa gathered as above and activated by Lymantrian prostatic secretion were injected artificially into Bombycian bursae copulatrices (Table 2). Three of five experimented females were fertilized, while the remaining two proved to be unfertilized. After examination, however, it was found that these unfertilized females also had received the semen in their bursae copulatrices and one of them had a small amount of spermatozoa in its receptaculum seminis. The poorer rate of success in this experiment than in the former seems to be due simply to the difficulty of operation caused by the delicacy of Lymantrian prostata, which is very small in size, being only some one-tenth that of Bombyx. The evidence herein obtained is sufficient to show that the prostatic secretion of Lymantria can give a quite normal activity to the spermatozoa of Bombyx. Since it was known from the author's previous study (Ômura, 1938) that the spermatozoa of Bombyx become fertile only when they are activated by mixing with prostatic secretion of its own, the results from the above two experiments seem to indicate that, so far as the function of activation of spermatozoa is concerned, the prostatic secretion of Lymantria is very near to, or the same as, that of Bombyx, and its function is not specific to its own spermatozoa.
Third, Lymantrian spermatozoa taken from the virgin male moths as in the case of Bombyx, and activated by adding with prostatic secretion either of Bombyx or of Lymantria were injected artificially into bursa copulatrix of Bombyx. In this case they never reached the receptaculum seminis, and, of course, never entered into the egg cells of Bombyx (Tables 3 and 4). However, it has been left for future study whether the Lymantrian spermatozoa make some progression in the Bombycian female genital organs, from the bursa copulatrix toward the receptaculum seminis. Anyhow, on the basis of the present study, it may be concluded that between Bombyx and Lymantria the difference in physiological character of spermatozoa in respect to time movement, is so decisive that Lymantrian spermatozoa cannot arrive at the egg cells in the Bombycian female sexual system, even if they are rid of those ecological and mechanical conditions which, in natural state, prevent the first step of their invasion into the Bombycian female genital organs. From the physiological aspect of spermatozoa of the Lepidoptera it is still considered from this investigation that the spermato-prostatic reaction does not represent any essential physiological function of spermatozoa.