Evidence for male genitalia detachment and female mate choice in the Australian stingless bee Tetragonula carbonaria

Mating systems are poorly understood for the majority of the world’s estimated 600 stingless bee species (Meliponini). It is assumed that in most species, a virgin queen takes a single nuptial flight, mates with a single drone and returns to the nest, using the stored sperm from this one event for the remainder of her life. Multiple genetic studies focused on stingless bee species from around the world have supported the hypothesis of single mating—monandry—by demonstrating shared paternity of workers within colonies. One possible mechanism for monandry is through male genitalia detachment during mating, which forms a residual mating plug inside the queen. Despite being thought to be the norm for stingless bees, male genitalia detachment has only been observed in a small number of species from the neotropics. Here I report on detailed observations of mating interactions for four queens of the Australian stingless bee Tetragonula carbonaria. Male genitalia detachment was observed in each case of copulation, providing the first evidence of male genitalia detachment in any Asian–Australian stingless bee lineage. Observations of the behaviour of queens also provide possible evidence for female mate choice in T. carbonaria. To more fully understand the mating system of T. carbonaria, further observations must be made of wild, natural copulation events, and the behaviour of the queen and the workers within the nest upon her return from the nuptial flight.