Research exposes fire ant's Achilles heel

Across large areas of the southern United States, the most social primate on Planet Earth has come into painful conflict with one of the world's most unlovable social insects - the South American fire ant, Solenopsis victor.

The unexpected appearance of the fire ants in suburbia near Brisbane's docklands two years ago sparked a costly campaign to eradicate it before it could spread across the continent.

Dr Michael Krieger and Dr Ken Ross, of the University of Georgia in Athens, in the midst of fire-ant territory, have recently identified a major gene that regulates the fire ant's social behaviour.

The gene, Gp-9, appears to have a role in energy storage, but also determines whether fire ant colonies will be ruled by a single queen (monogyne) or many queens (polygyne).

Krieger says there are two basic variants of the gene, that, in line with Mendel's laws, give rise to three possible combinations -- BB, Bb and bb.

Monogyne colonies have a lone Bb queen; she has sufficient energy to a hole in new territory, lay her eggs, and found the colony herself.

Polygyne colonies have bb queens -- they lack the energy to found new nests, so they drop in on existing polygyne colonies to join forces with resident queens. The workers recognise and tolerate these new arrivals.

There are no colonies with BB queens -- they don't found monogyne colonies, and if they drop in on a polygyne colony, within 15 seconds they are recognised and decapitated by alert workers.

The contrasting strategies convince Krieger and Ross that gp9 has a key role in social behaviour in fire ants.

Based on its similarity to a gene in the silkworm moth, they believe the gene codes for a pheremone receptor in the ant's nervous system. The receptor allows workers to detect the distinctive pheremone 'signature' that causes them to commit regicide, or lower the drawbridge to admit a new queen.

Many orchards now use decoys that mimic the mating pheremones of fruit flies and moths. Could the fire ant's gp9 receptor be a target for a pheremone-based pesticide that would sow chaos and confusion, causing fire ant colonies to self-destruct?