Queen signals in a stingless bee: suppression of worker ovary activation and spatial distribution of active compounds

Abstract

In most species of social insect the queen signals her presence to her workers via pheromones. Worker responses to queen pheromones include retinue formation around the queen, inhibition of queen cell production and suppression of worker ovary activation. Here we show that the queen signal of the Brazilian stingless bee Friesella schrottkyi is a mixture of cuticular hydrocarbons. Stingless bees are therefore similar to ants, wasps and bumble bees, but differ from honey bees in which the queen's signal mostly comprises volatile compounds originating from the mandibular glands. This shows that cuticular hydrocarbons have independently evolved as the queen's signal across multiple taxa, and that the honey bees are exceptional. We also report the distribution of four active queen-signal compounds by Matrix-assisted laser desorption/ionization (MALDI) imaging. The results indicate a relationship between the behavior of workers towards the queen and the likely site of secretion of the queen's pheromones.

Figure 1. Ovary activation of F. schrottkyi workers under different treatments.

(A), worker with inactivated ovaries, (B) detail of the inactivated ovary (C) worker with activated ovaries, (D) details of activated worker ovary and (E) Levels of ovary activation under different treatment: Control, queenright colonies; Queenless, queenless colonies treated with pure hexane; Extract, queenless colonies treated with queen cuticular extract.

Figure 2

MALDI-MS images reconstructed with ions m/z 303.36 [M+⁷Li]⁺ (C21) (A – front head, B- back head), 317.38 [M+⁷Li]⁺ (C22) (C – front head, D- back head), 345.41 [M+⁷Li]⁺ (C24) (E – front head, F- back head) and 359.42 [M+⁷Li]⁺ (C25) (G – front head, H- back head). Optical images of dissected front (I) and back head (J) of queen.

Figure 3

MALDI-MS images reconstructed with ions m/z 303.36 [M+⁷Li]⁺ (C21) (A – dorsal metasoma, B- ventral metasoma), 317.38 [M+⁷Li]⁺ (C22) (C – dorsal metasoma, D - ventral metasoma), 345.41 [M+⁷Li]⁺ (C24) (E – dorsal metasoma, F- ventral metasoma) and 359.42 [M+⁷Li]⁺ (C25) (G – dorsal metasoma, H - ventral metasoma). Optical images of dissected dorsal-terga (I) and ventral-sterna metasomas (J) of queen.

Figure 4. Synthesis of 11-MeC21, 11-MeC23 and 11-MeC25.

Commercially available undecyl alcohol 1 (Aldrich, Stanheim, Germany) was converted to the bromide 2 and, subsequently, to the Wittig salt 3 by using triphenylphosphine in dry toluene. The salt 3 was then methylated at the α-position using n-butyl lithium and methyl iodide and submitted to a sequential Wittig reaction with commercially available aldehydes 4a and 4b, and aldehyde 4c (previously synthesized from tetradecan-1-ol by PCC oxidation). The resulting alkenes (5a, 5b and 5c) were hydrogenated to yield the target 11-methylated alkanes 6a, 6b and 6c.