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Having determined the sequence of the genes, Vander Meer and Choi used the relatively new technique of RNA interference (RNAi) to provide another test of the role PBAN plays in fire ant trail pheromone production.
Scientists dissolved the dsRNAof PBAN or its receptor in a water solution, injected it into ants, and made observations at 24, 48, and 72 hours after injection.
"When we used RNAi to suppress expression of either the PBAN gene or the PBAN receptor gene, the ants produced less trail pheromone" than ants that did not receive the treatment, Vander Meer says.
But the team also discovered that the PBAN gene is expressed in every stage of the fire ant's life cycle, which suggests that the gene has functions beyond pheromone production.
Choi and Vander Meer demonstrated this by suppressing expression of the PBAN gene in fire ant larvae, pupae, and adults, and then looking for any observable impact on treated ants.
Most importantly for future fire ant control efforts, brood-tending workers that fed on PBAN RNAi dissolved in sugar water regurgitated the RNAi to their hungry brood, which in turn died at a high rate, he says.
Once she's found a host plant, PBAN triggers production of the pheromone and a male comes to mate.
Minh-Tam Davis in Raina's lab cloned the PBAN gene, and Raina, in collaboration with Vic Vakharia of the Center for Agricultural Biotechnology, University of Maryland, successfully inserted the PBAN gene into a baculovirus.
Raina and colleagues then spent about 5 more years identifying PBAN's specific protein composition.
That effort paid off in July 1991, when Raina and two collaborators received a patent on PBAN - clearing the way for companies to seek licenses to turn the protein into a new, natural corn earworm control to replace chemicals.
Aside from the baculovirus approach, Raina and Kempe are also pursuing another strategy: The Production of nonprotein mimics to act as blockers of PBAN action and disrupt the insect's internal body functions.
The next step will be finding a PBAN blocker to disrupt corn earworm mating.
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