UC Davis scientists are changing their navel orangeworm research direction after a sixth grader showed that the major agricultural pest prefers pistachios over almonds and walnuts.

Conventional wisdom had been that navel orangeworms prefer almonds. "Everybody knows that navel orangeworms prefer almonds," said Walter Leal, UC Davis chemical ecologist and professor of entomology. However, after his 11-year-old son proved that notion wrong in an elementary school science fair experiment, Leal's lab has begun studying navel orangeworms' attraction to pistachios to find more effective methods of controlling the pest.

Navel orangeworm (Amyelois transitella) is considered the key insect pest of almonds and pistachios in California because the larvae feed directly on the nut meats, making them unsuitable for the marketplace. Navel orangeworm larvae also feed on walnuts, pomegranates and a number of other crops.

Leal's son, Gabriel Leal, prefers pistachios over all other nuts so he figured that the navel orangeworm would, too.

"Pistachios taste better," reasoned Gabriel.

Gabriel hypothesized that the insect would lay more eggs in pistachios than in almonds and walnuts, contrary to widely published research that indicates an almond preference. The sixth grader at Willet Elementary School in Davis set up a scientific experiment to prove his hypothesis.

"I thought, 'No way,'" Leal said. "No way would the navel orangeworm prefer pistachios over almonds."

Leal let him do the experiment anyway, figuring that despite a wrong hypothesis, Gabriel would learn about the scientific method and about an agricultural pest that wreaks havoc on California nut orchards.

Gabriel's research showed that the insects preferred pistachios.

"Gabriel got enough replicates to demonstrate that female navel orangeworms do prefer pistachios over walnuts and almonds," Leal said. "We are very excited with our little scientist's discovery. I reported 'our' findings at the state almond industry conference in Modesto. And these findings changed our research direction, because we are now interested in determining what chemistry in pistachios attracts female navel orangeworms."

Gabriel performed his research under the volunteer supervision and mentoring of his father's colleague, UC Davis chemical ecologist Zain Syed.

"It was a 'choice' experiment where Gabriel placed mated and gravid (egg-filled) females in a cage," Syed said. "He used four commercially available navel orangeworm traps (Ovitraps). One trap was filled with 50 grams of shelled pistachios, another with 50 grams of almonds, and a third with 50 grams of walnuts. The empty trap served as the control to check if the trap itself had any effects on attracting egg-laying moths. The eggs laid in the ovitraps were counted for two consecutive nights."

"Oviposition (egg-laying) attractants derived from almond oil are used to monitor female populations in the field," Leal explained, "but during hull split, the chemical from the natural source (crop) competes with the synthetic material in traps. If we use pistachio-derived attractants in the almond field there will be no competition throughout the flight season."

Paramount Farming Co. research entomologist Brad Higbee called the boy's findings "interesting, provocative and intriguing."

"It's provocative in the sense that we know little about the natural preference of the navel orangeworm (NOW)," said Higbee, who is based in Bakersfield. "NOW is a pest that attacks tree crops planted on over 1 million acres in California and it is the primary and most destructive pest on almonds and pistachios, which represent about 800,000 of those acres. About 152,000 are in pistachios. The economic impact of NOW damage varies from year to year, but it can easily reach $10 [million] -15 million for our company and much higher statewide."

"I find Gabriel's discovery intriguing," Higbee said, "as it relates to trapping studies we have conducted that suggest that NOW females lay more eggs on traps baited with pistachio kernels compared to almond kernels at certain times of the year in both almond and pistachio orchards."

Researchers and growers often use egg traps baited with a mixture of almond meal and almond oil to attract the pests. Higbee said that developmental studies conducted in Paramount's laboratory and in the USDA-Agricultural Research Service lab in Parlier confirm that NOW develops much faster when fed pistachios relative to almonds.

"That suggests," Higbee said, "that not only do NOW have preferences, but there may be biological advantages to the preferences they exhibit."