Repellent scent-marking behaviour of the sweat bee Halictus (Seladonia) aerarius during flower foraging

Several social bee species of the family Apidae use scent marks on flowers left by previous visitors to improve foraging efficiency, but scent marking has not been demonstrated in other social bees. Experiments were conducted to confirm the ability of the eusocial sweat bee Halictus (Seladonia) aerarius (Hymenoptera: Halictidae) to use scent marks to detect flowers within 3 min of foraging by the same individuals or by conspecifics. Rejection responses were evident on two plant species, Erigeron annuus and Justicia procumbens. The proportion of hovering rejection responses to visited flowers differed among plant species. Repellent responses to visited flowers of J. procumbens decreased without replenishment of nectar. We suggest that the duration of scent marks used by H. aerarius is not adjusted to nectar replenishment and that this bee uses different rejection responses depending on the resources expected when revisiting flowers. This strategy may be considered a basal trait in the bee's evolution.