Queens and workers are not morphologically differentiated in the primitively eusocial wasp, Ropalidia marginata. Upon removal of the queen, one of the workers becomes extremely aggressive, but immediately drops her aggression if the queen is returned. If the queen is not returned, this hyper-aggressive individual, the potential queen (PQ), will develop her ovaries, lose her hyper-aggression, and become the next colony queen. Because of the non-aggressive nature of the queen, and because the PQ loses her aggression by the time she starts laying eggs, we hypothesized that regulation of worker reproduction in R. marginata is mediated by pheromones rather than by physical aggression. Based on the immediate loss of aggression by the PQ upon return of the queen, we developed a bioassay to test whether the queen’s Dufour’s gland is, at least, one of the sources of the queen pheromone. Macerates of the queen’s Dufour’s gland, but not that of the worker’s Dufour’s gland, mimic the queen in making the PQ decrease her aggression. We also correctly distinguished queens and workers of R. marginata nests by a discriminant function analysis based on the chemical composition of their respective Dufour’s glands.
Supplementary material S1Flame ionization detection gas chromatogram of a Ropalidia marginata Dufour’s gland crushed in Ringer’s solution, evaporated to dryness and resuspended in pentane. Asterisk signifies contaminant from Ringer’s solution. Identities of peak numbers are given in Table 1. Compare the chromatogram of this extraction method with that obtained in S2 (PDF 34 kb)
Supplementary material S2Comparison of gas chromatograms of the same sample of a Ropalidia marginata Dufour’s gland extracted in pentane and analyzed by flame ionization detection (FID) and mass spectrometry (total ion chromatogram; TIC). Identities of peak numbers are given in Table 1 (PDF 188 kb)
Supplementary material S3Flame ionization detection gas chromatogram of a Ropalidia marginata Dufour’s gland crushed and extracted in acetone. Identities of peak numbers are given in Table 1. Compare the chromatogram of this extraction method with that obtained in S2 (PDF 19 kb)