The minimum number of sperm stored in the spermatheca of many individual females of Oncopeltus fasciatus (maintained at 20°–22° C on milkweed seed), estimated from the total count of fertile eggs laid after mating and isolation, is variable (100–1000, mean 400). This variability may result from very slow sperm transfer and the highly variable duration of copulation. Spermatozoa can survive at least 5 months, but the reserve is often completely depleted by egg fertilization. There is no correlation between the number of sperm stored and the egg production rate. The percentage of fertile eggs remains high (95%) while the number of stored sperm is above 100, but then falls linearly; this suggests that fertilization may be monospermic.

Summary

When the spermathecal glands are removed from young unmated queens and they are then naturally mated or artificially inseminated, only a small number of spermatozoa reach the spermatheca. Turgor of the spermatheca is at the same time reduced. Removal of one branch of the gland has very little effect.

When intact queens are inseminated with damaged spermatozoa, the spermatheca remains almost empty. Paralysis of the skeletal muscles in the queens abdomen caused by Microbracon poison results in a sharp reduction of sperm entering the spermatheca. Under such conditions, the sperm is not removed from the oviducts.

From these experiments it is concluded, that transfer of spermatozoa out of the oviducts into the spermatheca is a complex process in which the muscles of the queen, as well as the fluid of the spermatheca and it's glands, and the individual movements of the spermatozoa take part.