STUDIES ON SPERMATHECAL FILLING IN AEDES AEGYPTI (LINNAEUS). I. DESCRIPTION

¹ Department of Entomology, University of Maryland, College Park, Maryland

1. With the forced-copulation technique, the Bangkok strain of Aedes aegypti can ejaculate within the first five seconds of coitus but usually does so within 10 to 15 seconds. The male force-copulates for 31.3 seconds, and 82% of the females become inseminated. In 90% of them, spermatozoa reach two of the three thecae. With naturally-mated mosquitoes copulation is significantly shorter in duration, all of the females become inseminated and in 92% of them spermatozoa reach all three thecae.

2. The terminal chamber of the testis of an unmated and repetitively force-copulated male has about 700 spermatozoa. Each sperm duct has about 370 sperm. The seminal vesicles of unmated males have about 5000 spermatozoa, while the vesicles of repetitively force-mated males have about 930.

3. With rapid repetitive force-copulation, the male ejaculates progressively fewer spermatozoa into the bursa of each successive female. Sperm counts made on 6 ejaculates from one male varied from 254 to 2655.

4. Counts on spermatozoa remaining in the bursa after spermathecal filling indicate that 62% of them leave the bursa, and suggest that about 660 sperm reach the large theca and 486 fill one of the lateral thecae.

5. Most of the sperm deposited in the bursa quickly spread to the edges of the sac, and many become aligned on its ventral wall. The wall of the bursa greatly swells two to three minutes after insemination. Shortly thereafter the accessory gland secretion within the ejaculate begins to vacuolate and may be fully vacuolated within 10 minutes and remains vacuolated for at least 6 hours.

6. With forced-copulation, a few sperm may be capable of reaching the thecae within 18 seconds but in most cases sperm begin to reach the thecae between 30 and 45 seconds after coitus. Complete thecal filling can occur in 90 seconds and probably is terminated within the first five minutes or less after coitus. Following spermathecal filling many active sperm remain in the bursa for some time. Following spermathecal filling those sperm at the bursal orifice no longer make the U-turn towards the open spermathecal vestibule.

7. Spermatozoa within the isolated but intact male reproductive system may remain active for five to six hours in oil-covered saline whole-mounts. Spermatozoa released from seminal vesicles in oil-covered saline drops exhibit four types of movement: (a) brief, rapid, explosive, progressive locomotion, (b) rapid synchronous coiling when the cells are in dense clusters and the head is at certain interfaces, (c) smooth undulations in situ, and (d) irregular undulations or oscillations. The heads of sperm of Aedes become oriented in the direction of a moving stream.

8. Sperm released from the seminal vesicles may become strongly oriented toward the male accessory glands and its exudate, and to freshly excised vaginal tissues, but they do not specifically congregate about these tissues in oil-covered saline whole-mounts. Seminal vesicle sperm do not become oriented to freshly. excised fat body, testes, somatic muscles, bursa, female accessory gland or its duct, spermathecae or their ducts, ovary, common oviduct, or a freshly laid egg.