Each year in the United States, fire ants cost $7 billion for control, damage repair, and medical care. They infest millions of acres in urban, agricultural, wildlife, recreational and industrial areas.
In order to combat the the red imported fire ant, scientists at the USDA’s Agricultural Research Service are studying pheromones that are secreted by the ants. Pheromones signal alarm, mark trails to food, attract workers to brood and the queen, and unite males and females for mating.
Entomologist Man-Yeon Choi and chemist Robert Vander Meer have shown for the first time that a neuropeptide called pheromone biosynthesis activating neuropeptide (PBAN) activates production of trail pheromones in ants.
PBAN was first discovered by ARS scientists in Beltsville, Md., in the 1980s. They found that the hormone regulates sex pheromone production in female moths. Since then, scientists have found that other insects, including cockroaches, have this type of PBAN family peptides made of two or more amino acids.
Choi injected fire ant workers with PBAN peptides and found a significant increase in pheromone production. He and Vander Meer also identified the DNA sequence of both the PBAN gene and receptor gene, which allowed them to test the function of PBAN in trail pheromone production using a new technique called RNA interference (RNAi). This involves taking normally single-stranded RNA from a gene and making double-stranded RNA (dsRNA) that can be used to suppress that gene’s expression.
When scientists injected dsRNA of either the PBAN gene or receptor gene into ants, they found that ants produced less trail pheromone. They also discovered that adult ants and larvae injected with PBAN-RNAi had significant mortality, compared to ants that didn’t receive the injection. Pupae that received the treatment had delayed development and a high death rate.
“This gene has many different roles. When we disrupt the expression of it with RNAi, we observe multiple effects in immature stages as well as in adults,” said Vander Meer.
The scientists also applied their PBAN RNAi work to the corn earworm — a moth species that is a serious crop pest.
“Our moth study was very extensive,” Vander Meer said. “We fed the PBAN RNAi to corn earworms in their standard laboratory diet, and it had dramatic effects.”
Those effects included a decrease in growth rate and the inability to develop from larvae into pupae. Female moths that survived to adulthood had decreased amounts of sex pheromone.
The scientists plan to investigate whether other pheromones are activated by PBAN, and if dsRNA can be used for fire ant control.
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