Venom sac proteins of red imported fire ant queens (Solenopsis invicta): characterization, expression and function

The venom of red imported fire ants (RIFA), Solenopsis invicta, primarily contains piperidine alkaloids with only 0.1% of the total venom being protein. Four proteins have been identified in worker RIFA venom: Sol i 1, Sol i 2, Sol i 3, and Sol i 4. Two proteins have an identity with proteins from yellow jackets and hornets, but Sol i 2 and Sol i 4 are unique to fire ants. Although proteins comprise only a small component of the venom of RIFA they have garnered research interest, particularly because some people react adversely to the proteins when stung by the notorious workers. Our efforts build upon this base, but target the previously unstudied venom proteins of the queens. Here, we compare the protein sequences of worker and queen venom sac, and show that queens produce two proteins that differ but are homologous to two worker venom proteins. We also report the successful expression of the queen proteins, a critical step for x-ray crystallography and the testing of functions, but one which proved to be highly challenging. Driving this research has been the exciting possibility that the proteins serve as pheromones involved in colony regulation, particularly the cannibalization of sexualized larvae by workers under certain circumstances. Identification of the pheromone source could be exploited to provide a potentially powerful tool for the management of this devastating pest. The testing of this potential function is currently in progress.