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Title: Multiple functions of fire ant, Solenopsis invicta, mandibular gland products

item Choi, Man-Yeon
item Vander Meer, Robert - Bob

Submitted to: Physiological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2015
Publication Date: 5/29/2015
Citation: Choi, M.Y., Vander Meer, R.K. 2015. Multiple functions of fire ant, Solenopsis invicta, mandibular gland products. Physiological Entomology. doi: 10.1111/phen.12102.

Interpretive Summary: The red imported fire ant, S. invicta, is among the world’s 100 worst invasive alien species. In the United States this ant species infests more than 320 million acres in 13 southern tier states and Puerto Rico and are spreading northward. It is estimated to be responsible for almost $7 billion annually in damage repair, medical care, and control costs. The affected economic sectors are broad ranging and include households, electric service and communications, agriculture, schools and recreation areas. In the last decade S. invicta has changed from an invasive pest ant in the United States to a global problem, with infestations occurring in Australia, Taiwan, mainland China, Mexico and many Caribbean Island countries. Global commerce ensures that fire ants will be distributed to compatible habitats throughout the world. Thus, novel control methods are needed and could result from manipulation of the fire ant alarm pheromone to disrupt mating flights or to in some way disrupt alarm pheromone production that could interrupt the normal insularity of fire ant colonies to pathogens, parasites, and other intrusions. In the present study, Scientists of the Imported Fire Ant and Household Insect Unit at the Center for Medical, Agricultural and Veterinary Entomology, USDA, ARS, Gainesville, FL have explored the changes in the amount of alarm pheromone accumulated in the mandibular glands of workers, female and male alate sexuals, and queens from the time they eclose as adults to late in their lifespan. It was discovered that the pattern of alarm pheromone accumulation is different in the above distinct female castes and mating status. The results presented here could be lead to an understanding of how the alarm pheromone is used by fire ants in the various contexts of workers, female alates, and queens. This is the initial step in developing novel, non-insecticide methods for fire ant control based on the interference of alarm pheromones in colony defense, mating flights, and colony development.

Technical Abstract: : Alarm pheromones are an essential part of a complex of pheromone interactions that contribute to the maintenance of colony integrity and sociality in social insects. Recently, we identified 2-ethyl-3,6-dimethylpyrazine as an alarm pheromone component of the fire ant, Solenopsis invicta. We continued to explore the ontogeny of alarm pheromone production in workers, female and male alate sexuals, and queens. In workers, alarm pheromone production commenced in the mandibular glands of callow fire ant workers (~45 pg/worker) directly after eclosion, and rapidly increased to a maximum at the brood tender stage (~260 pg/worker). Then, pheromone accumulation sharply declined with the oldest temporal caste, foraging workers. In female alates, the late pupal stage had detectable amounts of alarm pheromone and after eclosion reached a maximum (~790 pg/alate) when the female alates were mating flight ready. Interestingly, a large amount of alarm pheromone was lost (~280 pg/queen) in the 30-60 minute duration of a mating flight, which strongly supports the involvement of alarm pheromone in mating flights, including flight initiation, male lek formation, and mate location. Workers and female sexuals have different patterns of alarm pheromone production. Workers have a uni-modal pattern, whereas female sexuals have a bi-modal pattern of alarm pheromone accumulation. The large accumulation of alarm pheromone followed by a decrease to trace amounts in mature mated queens is correlated with worker numbers (colony size). If the biosynthesis of the alarm pheromone remains constant throughout the life of the female sexual, then it is the rate of utilization that dictates whether or not the amount of alarm pheromone increases, decreases, or stays the same. Another scenario is that the biosynthetic enzymes and/or endocrinal factors involved in alarm pheromone production are turned on or off depending on the physiological state of the female sexual. The bi-modal accumulation would then require two separate cycles of activation and deactivation.