ECOLOGY:

Even though ants are fascinating insects -- highly adaptable with complex communication and social arrangements -- they're sometimes highly devastating pests. Solenopsis invicta -- red imported fire ants -- are one of them.

Even though these critters are only a few millimeters long, they're nevertheless aggressive invasive pests in the United States and a few other countries. The United States spends a few billion dollars every year dealing with them; they can disrupt agriculture, short out the electric wiring of traffic lights, and are extremely difficult to eliminate.

Current pesticides and toxic baits aren't ideal control options, especially in environmentally-sensitive locations. This is because they're nonselective, i.e. they target (beneficial) insects in addition to red imported fire ants.

Max Suckling (New Zealand Institute for Plant and Food Research) and coworkers have worked towards developing a pesticide that's selective for red imported fire ants. They have disrupted ant pheromone trails, disorienting the ants, likely hindering their ability to bring food back to their nests.

Principles and experimental setup.

Red imported fire ants use a chemical known as E,E-alpha-farnesene ("green apple scent") to find the way back to their nest. The scientists synthesized a very similar chemical, Z,E-alpha-farnesene, which the ants cannot distinguish from their pheromone, to disrupt ant pheromone trails.

The scientists collected ants from the field, or started their own colonies with queens collected from the field. They first deprived the colonies of food (not water).

They then placed a (presumably dead) cricket and a ball of sugar-dampened cotton across from the colony. Once ants had begun to move back and forth (forming a trail of pheromones), video tracking (15 frames per second) and trail disruption experiments were begun.

The scientists placed a small drop of Z,E-alpha-farnesene (mixed with petroleum ether), at one of two concentrations, on a piece of filter paper within 1 centimeter of an ant trail. Filter paper dropped with pure petroleum ether was used as a control.

The ants were monitored for at least one minute before and at least one minute after attempted trail disruption. The position of up to 25 individual ants in every 5-second frame was recorded with custom software.

Pheromonal trail disruption.

The scientists readily observed that the ants' trail broadened (i.e. was partially disrupted) in less than 30 seconds after application of 30 micrograms Z,E-alpha-farnesene. Control filter paper (no Z,E-alpha-farnesene) had no statistically significant effect on trail integrity.

Within a few minutes, no clear trail at all was observed after application of 300 micrograms Z,E-alpha-farnesene. In other words, the ant trail was completely disrupted with a fake pheromone.

Overall evaluation.

For this technique to be useful regarding invasive fire ant colony disruption, a technology must be developed to slowly release Z,E-alpha-farnesene in the path of the ants. It's conceivable that plants could be genetically modified to synthesize and release the fake pheromone, continually confusing the ants.

Furthermore, it's unlikely that trail disruption entirely prevents the ants from eventually bringing food back to their nests. Delayed return is more likely; the costs this imposes on food collection (i.e. its effects on colony survival) require further research.

Despite the risk of failure, this approach of using very small quantities of chemicals (low toxicity risks) to selectively disrupt imported red fire ant feeding (not other insects) has a huge potential payoff. It's well worth continuing these studies to see if they're applicable in a real-world setting.

for more information:
Suckling, D. M., Stringer, L. D., Bunn, B., El-Sayed, A. M., & Vander Meer, R. K. (2010). Trail Pheromone Disruption of Red Imported Fire Ant Journal of Chemical Ecology, 36 (7), 744-750 DOI: 10.1007/s10886-010-9810-6