John Beck, U.S. Department of Agriculture research chemist in Albany, Calif., is leading the charge to build the proverbial better ‘mouse trap.’ Only in this case, it's finding a better Navel orangeworm (NOW) attractant to use in trap monitoring.
“We’ve pretty much turned our full attention to just pistachios,” said Beck with USDA's Agricultural Research Service (ARS).
“We’re trying to find the magic elixir which consistently provides effectiveness throughout the season.”
Beck and other ARS researchers have spent seven years developing a new lure - a blend of five natural kairomones semiochemicals. Unlike pheromone which is released by one sex to attract the other, kairomones are volatile compounds emitted by one species to produce a behavior from another.
Three chemicals selected for the experimental blend are produced by the almond tree. The other two are emitted by fungal spores, including Aspergillus flavus and A. parasiticus, found on almond trees.
Beck says a challenge with pistachio trees is emitting a much more complex group of volatiles than almonds and at much lower levels. The pistachio complex also is dominated more by terpenoids or terpenes than almonds.
“With pistachios, we looked for this same recipe (as almonds) but realized pistachios, for most of the pre-harvest life, do not allow many fungi to develop – a time we noticed when NOW semiochemicals are released,” Beck said.
“We have hypothesized that this inhibition of fungal development -- not growth per se -- is due to the large amount of monoterpenes, many of which have demonstrated antimicrobial activity in other systems.”
Based on three years of preliminary trials in commercial orchards, the new lure appears seven times more powerful than almond meal-based traps.
Pistachio growers currently have two types of NOW monitoring traps - each one with limitations. The pheromone trap uses female scents to attract nearby males. Since the lure is based on female pheromones, the lure does not alert users to female moth activity.
And, pheromone traps can be “shut down” by mating disruption, which involves blanketing an orchard with female pheromones to confuse male moths and interfere with the ability to find mates.
The NOW egg trap, used to monitor ovipositing, involves a cylinder that holds ground nut meal to attract females. Yet counting the eggs can be tedious. The meal-based lure can lose effectiveness in pistachios after June, even while high numbers of moths may be present.
Brad Higbee, director of entomology research for Wonderful orchards in Shafter, has collaborated with Beck and his predecessor Jim Roitman for years to develop better NOW attractants.
So far, trials in commercial pistachio orchards are promising.
Higbee says a big advantage over pheromone traps, particularly in orchards where mating disruption is used, is the new lure attracts male and female moths. It also appears to work better than egg traps early in the season.
“In pistachio, it is also much more attractive than nut meals but has the same limitation as the nut-based attractants after June,” Higbee said.
“For reasons not well understood, both of these attractants are not very effective in luring moths to traps in pistachios after June, even though NOW moths are abundant."
Egg traps can have the same limitation.
This is not true for the pheromone lure, which is effective in almonds and pistachios season long, he says.
In almonds, Higbee says the kairomone lure is much more attractive than nut meals all year when used in a sticky trap.
Field testing is just part of the process. The researchers also are tackling how to keep the proper ratio of kairomones stable since evaporation occurs at different rates.
They also are working with Suterra of Bend, Ore. to develop a commercial lure platform for growers, says Higbee. One idea is to impregnate a small pouch, and users would simply peel off the cover to release the compounds.
In trials, the researchers hung a small plastic vial containing about a half teaspoon of the liquid inside a delta trap, but Beck says they want to make this more user friendly.
Higbee, who has worked on the new pheromone-based Biolure and the kairomone lure, is developing correlations between the various trap types and damage risks. He hopes to have results in about a year.
In addition to Higbee, research collaborators include ARS researchers Doug Light, Noreen Mahoney and Wai Gee at the Albany station, and Dan Cook in Parlier, Calif.
The work is partially funded by the California Pistachio Research Board.