Assessing Sperm Quality in Stingless Bees

Although stingless bees have a great potential as commercial pollinators, their exploitation depends on the successful reproduction of colonies on a large scale. To do so, it is essential to develop accurate diagnostic tools that facilitate a better understanding of the reproductive biology of stingless bees. Sperm counts, sperm morphology and sperm viability (the relative proportion of live to dead sperm), are key parameters assessing semen quality and potential fertilization success. Here we present standardized protocols to assess these three parameters. We used Scaptotrigona aff. depilis (Moure) as a study model. Semen extractions from the seminal vesicles were found to yield better results when performed in mature rather than in younger males. For morphology and viability analyses, the best semen dilution on Hayes solution was adding 120 µl to the contents of the two seminal vesicles. For sperm count, however, we recommend a higher dilution (1.000 µl). Sperm viability values were higher when Hayes solution was adjusted to pH 8.7 and no difference were found in sperm viability when analyzing fresh semen, and semen collected 1, 3 and 5 hours prior to the analyzes. However, we found a significant decrease in sperm viability when analyzing sperm collected 24 hours beforehand. The protocols seem sensitive and efficient, and show great potential to be used in other stingless bee species.