Characterization of Queen Supergene Pheromone in the Red Imported Fire Ant Using Worker Discrimination Assays

Area of Science:

• Chemical Ecology
• Animal Behavior
• Invasive Species Biology

Background:

• Social organization in ants, like the red imported fire ant (Solenopsis invicta), is regulated by chemical communication.
• Colony structure (monogyne vs. polygyne) is determined by the presence or absence of the Sb supergene.
• Workers distinguish between queens based on genetic and reproductive status, crucial for colony integrity.

Purpose of the Study:

• To identify the specific chemical signals used by red imported fire ant queens to communicate their supergene genotype and reproductive status to workers.
• To investigate the synergistic effects of different chemical compounds in eliciting worker acceptance behaviors.
• To elucidate the chemical basis of social organization in this invasive ant species.

Main Methods:

• High-throughput behavioral assays were employed to test worker responses to queen extract fractions and synthetic chemical blends.
• Paper dummies were dosed with various chemical compounds, including unsaturated hydrocarbons and polar fractions from queen extracts.
• Worker acceptance of dummies was quantified to determine the signaling roles of different chemical cues.

Main Results:

• The queen supergene pheromone was identified as a blend of monoene and diene unsaturated hydrocarbons.
• Unsaturated hydrocarbons alone were insufficient for worker discrimination; they required association with other compounds signaling queen fertility.
• Piperidine alkaloids (venom alkaloids) did not mediate queen reproductive status signaling; more polar compounds were implicated.

Conclusions:

• Chemical communication, specifically unsaturated hydrocarbons, plays a key role in signaling queen supergene status in Solenopsis invicta.
• Queen reproductive status is signaled by compounds distinct from piperidines and unsaturated hydrocarbons, requiring a synergistic interaction for worker acceptance.
• Understanding these chemical cues is vital for managing this significant invasive pest and model organism.