Scores from S.invicta queen supergene pheromone discrimination assays

Ants use chemical signals to communicate for various purposes related to
colony function. Social organization in the red imported fire
ant, Solenopsis invicta, is determined by
the Sb supergene, with colonies of the monogyne
(single-queen) form lacking the element and colonies of the polygyne
(multiple-queen) form possessing it. Polygyne workers accept new
reproductive queens in their nest, but only those carrying Sb;
young winged queens lacking this genetic element are executed as they
mature sexually in their natal nest or as they attempt to enter a foreign
nest to initiate reproduction after mating and shedding their wings. It
has been suggested that queen supergene genotype status is signaled to
workers by unsaturated cuticular hydrocarbons, while queen reproductive
status is signaled by piperidines (venom alkaloids). We used
high-throughput behavioral assays to study worker acceptance of paper
dummies dosed with fractions of extracts of polygyne queens, or blends of
synthetic counterparts of queen cuticular compounds. We show that the
queen supergene pheromone comprises a blend of monoene and diene
unsaturated hydrocarbons. Our assays also reveal that unsaturated
hydrocarbons elicit discrimination by polygyne workers only when
associated with additional compounds that signal queen fertility. This
synergistic effect was obtained with a polar fraction of queen extracts,
but not by the piperidine alkaloids, suggesting that the chemical(s)
indicating queen reproductive status are compounds more polar than
cuticular hydrocarbons but are not the piperidine alkaloids. Our results
advance understanding of the role of chemical signaling that is central to
the regulation of social organization in an important invasive pest and
model ant species.