Abstract
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.
Highlights
In order to exploit the great potential of stingless bees as commercial pollinators, it is of great importance to improve management and optimize practices to produce colonies on a large scale
Semen was more collected from the seminal vesicles of mature males (Fig 5) rather than younger ones (Fig 6), as semen had already migrated from the testicles to the seminal vesicles in mature males only
Sperm counts in S. aff. depilis resulted in an average (± SE) of 1,487,778 ± 36,044 sperm cells per male
Summary
In order to exploit the great potential of stingless bees as commercial pollinators, it is of great importance to improve management and optimize practices to produce colonies on a large scale. Semen quality is known to determine male reproductive success across taxa (Simmons, 2001). Semen quality can be affected by factors such as the number, morphology and viability of sperm (Garófalo, 1980; Simmons, 2001; den Boer et al, 2009). Garófalo (1980) evaluated the amount of semen produced by the males and stored in the female’s spermathecae in different species of bees, including eight stingless bees, and found that there is no relationship between social levels and the amount of sperm found in females and produced by males. Camillo (1971) noted an increase of 2.35 times in the number of sperm of giant Friesella schrottkyi (Friese) males (produced occasionally when an unfertilized egg is raised on a royal cell) compared to what is found in common males.
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