A new method for distinguishing colony social forms of the fire ant Solenopsis invicta

Authors: Shoemaker, David; Ascunce, Marina

Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2009
Publication Date: 5/24/2010
Citation: Shoemaker, D.D., Ascunce, M.S. 2010. A new method for distinguishing colony social forms of the fire ant Solenopsis invicta. Journal of Insect Science. 10(73):1-11.

Interpretive Summary: Fire ants are considered significant ecological, agricultural, and public health pest throughout their invasive range in the U.S.A. Two distinct forms of colony social organization (single queen and multiple queen colonies) occur in the red imported fire ant and this major difference in social organization is associated with genetic variation at a single gene (Gp-9). Scientists at the Center for Medical, Agricultural, and Veterinary Entomology, USDA-ARS, Gainesville, Florida developed new molecular assays to distinguish the two distinct colony social forms of fire ants based on surveying variation at Gp-9 previously shown to be informative in distinguishing the two social forms. Survey results demonstrate these new molecular assays consistently and accurately identify the variable nucleotides at these informative sites. The new method is robust, cost-effective, sufficiently high-throughput, and accurate for determining colony social form of fire ants. The new molecular assays developed make accurate assignment of social form straightforward. The ability to accurately classify colonies to social form is critical to management strategies, to constructing predictive models of their spread and expansion, and to assessing the potential of successful eradication of S. invicta in newly invaded areas.

Technical Abstract: Two distinct forms of colony social organization occur in the fire ant Solenopsis invicta: Colonies of the monogyne social form are headed by a single egg-laying queen, whereas those of the polygyne social form contain multiple egg-laying queens. This major difference in social organization is associated with genetic variation at a single gene (Gp-9) whereby all polygyne queens possess at least one b-like allele while monogyne queens lack such b-like alleles and instead harbor B-like alleles only. Further, a recent study revealed that all b-like alleles in polygyne queens consistently contain three diagnostic amino acid residues: possession of only one or two of these critical residues is not sufficient for polygyny. We developed TaqMan® allelic discrimination assays to survey the variable nucleotide sites associated with these three critical amino acid residues and then validated our assays by surveying nests of known social form from the species’ introduced (U.S.A.) and native South American ranges as well as by comparing our results to Gp-9 sequence data from a subset of samples. Our survey results demonstrate these new molecular assays consistently and accurately identify the variable nucleotides at all three sites characteristic of the B-like and b-like Gp-9 allele classes, allowing for accurate determination of colony social form.