Studies with psyllid pheromones show that the insect’s behavior is altered when it is infected by the HLB-causing bacterium Candidatus Liberibacter (CLas). This makes it difficult to produce a commercial psyllid-control product based on the insect pheromone, Brazil’s Fundecitrus has concluded.
“The sexual pheromone is an attractant produced by the female of the species, which promotes behavioral changes in male individuals of the same species,” stated Fundecitrus researcher Haroldo Volpe. He said researchers studied whether the psyllid’s sexual pheromone existed and, if it did, which molecule causes the male’s attractiveness.
The objective of the Fundecitrus study was to find an attractant to place in a yellow sticky trap to combine physical attraction (trap color) with chemical attraction (pheromone). At the time, the number of insects captured in traps often did not match the increase in trees contaminated with the bacteria.
The studies were carried out with psyllids that were not contaminated with CLas. The insects were raised in controlled conditions and in large quantities.
“Our objective was to find the compound that the female used to attract the male,” Volpe said.
The compound found in the research was acetic acid. It was necessary to understand how much of the substance was needed to attract the male psyllid. The test used for this purpose is olfactometry. After understanding the ideal dose to attract the insect, it was time to understand how the pheromone would be produced in the field, using an industrial formulation.
CALIFORNIA COLLABORATION
Volpe and other researchers went to California. There they were joined by Walter Leal, one of the world’s leading experts in chemical ecology and insect smell. Leal led the project from the initial stage.
“We managed to find a formulation that attracted more male insects to the trap when compared to traps that did not have this formulation,” Volpe said. “We thought we had a product that would actually attract psyllids; we were very close to a commercial product.”
“We didn’t know if this insect produced a sexual pheromone, so we carried out a detailed behavioral study to reach the conclusion that females actually produce the pheromone that attracts males,” Leal said.
Leal added that Fundecitrus discovered that the male psyllid, once infected, has an affected olfactory system, “so that it requires a much larger amount of pheromone to obtain the same effect.”
RESULTS DIFFERED BY REGION
The researchers returned to Brazil to test their product. The expectation was that the formulation would attract the male psyllid to the traps. That was not the case, however. In an organic orchard in Brazil, the formulation didn’t have the same effectiveness that it did in the United States.
The studies then focused on understanding why the formulation worked in the United States, but not in Brazil.
“At the time there weren’t as many contaminated insects in California as there were here in Brazil,” Volpe said. “That’s when we started to consider the possibility of the disease affecting the behavior of the male in relation to the formulation we had developed.”
Researchers began to breed contaminated insects so that this behavior could be confirmed. “We took the concentration of the pheromone approved in an olfactometer and which attracted uncontaminated insects, and we realized that this concentration did not attract contaminated insects,” Volpe said. “We then began to increase the concentration in the olfactometer, and we understood that to attract the contaminated insect we needed a concentration 50 times greater. We then saw that this project lost its commercial bias, since in several regions we have more than 60% of insects already contaminated with the bacteria and, in others, we have a percentage much lower than that.”
“There is no way to produce formulations to attract contaminated and uncontaminated insects at the same time,” Volpe said. “If you have a low concentration, you will only attract uninfected insects. If it is a high concentration, only the infected ones are attracted. This makes the production of this product unviable.”
Fundecitrus researchers confirmed what others had reported: that there are in fact behavioral changes in the insect infected with the bacteria. Insects with and without the bacteria respond in different ways.
Source: Fundecitrus
Share this Post
Sponsored Content