Fire ants cause a large number of stings each year — the US Department of Agriculture estimates that, in infected areas of the US, between 30 percent and 60 percent of the human population is stung each year, and about 1 percent of those cases leads to a severe allergic reaction.
"People in regions like the Amazon region in Brazil, by end of afternoon, before the sun sets, pets, animals, and kids must be removed inside their homes and don't leave during the night because this is the time when the ants usually … produce a mass attack," says Mario Palma from the University of São Paulo State in Brazil, who led a proteomic investigation of the makeup of fire ant venom. "The envenomation is huge." The results of his study were published online in the Journal of Proteome Research in August.
To get a full characterization of fire ant venom components, Palma and his colleagues combined both a two-dimensional gel electrophoresis approach and a high-performance liquid chromatography MS/MS approach. This allowed them to identify 46 proteins, some of which were not previously known to be in fire ant venom. The proteins also play a number of roles. "Some of these proteins are related to envenomating ... but half of the material, 50 percent of the proteins, present other functions," Palma says.
The 21 venom proteins identified include a number of allergens, neurotoxins, and metalloproteinases. Neurotoxins, Palma says, are primarily found in the venom of solitary hunters like scorpions or spiders, rather than social insects like fire ants — indeed, he adds that they had not been previously described in fire ant venom. Neurotoxins, he says, could lead to hallucinations or other neurological effects in affected people. And metalloproteinases break down the connective tissues between cells, possibly leading to edema.
In addition, Palma says that they uncovered proteins that gave researchers a better peek into the ants' biology. For example, the venom contains a number of proteins used for chemical communication, like pheromone transporters.
As some ants release venom, others pick it up as they walk. "That means that when the insect involved in the attack just touches the substrate where they are walking on, they can identify the presence of the pheromone already activated by the transporters," he says, adding that "this makes the stinger ants much more aggressive than they were before. … This is a kind of public relations of fire ants. The proteins make the fire ant colony much more aggressive, much more ready for a mass attack."
With a better understanding the makeup of the venom, Palma says that better immunotherapies or anti-serums can be developed to treat or prevent reactions to fire ant stings.