Cuticular lipids of red imported fire ants: Analysis of low-volatility semiochemicals

Some semiochemicals involved in communication between ants are thought to act over a short distance or by direct contact. These low-volatility substances can be difficult to detect by gas chromatography. We have developed methods to analyze short-range semiochemicals from the red imported fire ant, Solenopsis invicta. Pentane washes of fire ant cuticle were fractionated on silica and the polar cuticular lipids were separated on a C18 reverse-phase column with a four-solvent gradient. Fatty acids elute early, and some fractions in this region were captured by the major chemosensory protein of the worker antenna, CSP1. Fatty acid esters elute later, and a fraction in this region was captured by Gp-9B, a hemolymph and antennal protein of unknown function. Comparison of cuticular washes from foragers and nurses shows that nurses display a unique cluster of less polar substances. Fractions that interact with specific olfactory binding proteins, or that are characteristic of workers performing specific tasks, can be chemically identified by mass spectrometry and their functions may be further studied in behavioral assays.