Pheromone sought to disrupt insect mating | Harvests

Jules Bernstein University of California-Riverside

A chemical that disrupts the mating of “bad” weevils and prevents them from destroying avocados is being researched by scientists at the University of California-Riverside. Avocado weevils are small, long-snouted beetles. They bore through fruit to lay eggs. Weevil larvae or grubs burrow into avocado seeds to feed.

“They are extremely difficult to control because they spend most of their time deep inside the fruit where they are well protected from insecticides and natural enemies,” said Mark Hoddle, biocontrol specialist at UC-Riverside. “Insects are also understudied, making information about them difficult to obtain.”

One pest control strategy is to introduce other insects that feed on them. But that’s unlikely to work because the weevils’ natural enemies appear to be rare in areas where the pest is native, Hoddle said.

He works with Jocelyn Millar, an insect-pheromone expert at UC-Riverside. They lead an effort to find the weevil pheromone. They plan to use it to monitor pests and prevent them from breeding in avocado orchards.

“We could flood avocado orchards with so many pheromones that males and females can’t find each other, and therefore can’t reproduce,” Hoddle said. “This would reduce fruit damage and allow growers to use fewer insecticides.”

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Alternative control strategies could include mass trapping using the pheromone as a lure or an “attract and kill” approach. This is where the pheromone attracts the weevils to small sources of insecticide.

Hoddle and UC-Riverside entomology researcher Sean Halloran captured the chemicals that avocado weevils release into the air. Possible formulas of pheromone compounds have been identified from crude extracts and are currently being synthesized in Millar’s lab.

“Weevil pheromones have complicated structures. When made in the lab, they can have either left-handed or right-handed shapes,” Hoddle said.

Initially, Millar’s group mixed the two forms to see if the mixture would work as an attractant. It’s cheaper to make the mix than the individual left or right handed shapes. Fieldwork in Mexico with the pheromone cocktail has not had much response from the weevils. This suggests that one of the forms of the mixture could antagonize the response to the other.

The researchers plan to synthesize individual forms of the chemicals and test the insect response to each in Mexican avocado orchards.

As import levels of avocados from Mexico increase, the risk of an accidental weevil invasion also increases. Hoddle said he hopes the pheromone will be successfully identified and used to reduce the risk the pest poses to avocado growers.

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Jules Bernstein is senior public information officer at the University of California-Riverside.

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