Efficiency of sperm use for fertilization and the pattern of sperm decrease in the female sperm storage organ of the bean bug, Riptortus clavatus Thunberg (Heteroptera : Alydidae)

Abstract

In Riptortus clavatus, females received about 550 sperm from a male during one copulation. The number of sperm remaining in the sperm storage organs (spermathecae) decreased exponentially as the days after copulation increased. The pattern of sperm depletion was almost in accord with that estimated from the oviposition pattern. The efficiency of sperm use (=number of sperm that fertilize eggs/total number of sperm released from spermathecae) was approximately 30% and was stable throughout the entire reproductive period. A copulation interruption experiment indicated the following : the percentage of sperm used for fertilizing all eggs laid by females was nearly 30% of the total number of sperm initially received from males during an insemination (irrespective of sperm number). These results suggest that the number of sperm remaining in the female sperm storage organs was influenced by the utilization of the sperm for egg fertilization, and the consumption ratio was approximately egg : sperm= 1 : 3.