The Effect of Semen Dilution on the Number of Spermatozoa Entering the Spermatheca of the Queen Honey Bee (Apis mellifera L.)

Abstract

This study aimed to determine whether the addition of diluent to fresh semen before injection affects the number of spermatozoa entering the spermatheca of the instrumentally inseminated queens. The queens reared by the grafting method were introduced into mating nucs one day before adult emergence. When 7-day old, the queens were allocated into four groups for the following instrumental insemination treatments. The queens in group 1 and group 3 were inseminated with 4 µl and 8 µl fresh semen, respectively (FS - 4 µl and FS - 8 µl). In group 2, the queens were inseminated with 4 µl fresh semen diluted 1-fold with NaCl solution (DS - 8 µl). In group 4, the queens were inseminated with 8 µl fresh semen diluted 1-fold with NaCl solution (DS - 16 µl). Each queen was dissected after the onset of oviposition for counting the number of spermatozoa in the spermatheca. There was not a significant difference in spermatozoa number between queens inseminated with 4 µl FS (2.57 million) and 8 µl DS (2.68 million). The queens inseminated with 16 µl DS (3.51 million) had fewer spermatozoa than the queens inseminated with 8 µl FS (4.46 million). The queens inseminated with 16 µl DS had more spermatozoa (3.51 million) than the queens inseminated with 4 µl FS (2.57 million, and 8 µl DS (2.68 million). The results revealed that the addition of 1-fold diluent to 4 µl fresh semen did not alter the number of spermatozoa. In contrast, adding 1-fold diluent to 8 µl fresh semen adversely affected the number of spermatozoa entering the spermatheca.