Sterile moth technology to target Navel orangeworm in tree nuts

Sterile moth technology to target Navel orangeworm in tree nuts

The PBW program has been a resounding success; there have been no native pink bollworm detections since Spring 2012.

To combat one of its major insect pests, the pistachio industry would like to take a page from the playbook of cotton growers and their highly successful pink bollworm (PBW) eradication program.

The nut growers’ target – it also plagues walnuts and almonds – is the Navel orangeworm (NOW), a vector for aflatoxin that is under increased scrutiny from pistachio processors.

The objective of a NOW control pilot project would be to do what the pink bollworm program has done, rearing and sterilization of massive numbers of moths per day. The project is in “the very preliminary stage,” said Bob Klein, manager of the California Pistachio Research Board.

The PBW program has been a resounding success; there have been no native pink bollworm detections since Spring 2012.

Klein said there is disagreement among researchers as to whether sterile NOW moths could be produced and in high numbers as is done with the PBW. Their physiology is, of course, different.

But if the objective is reached, the payoffs could be considerable. It would mean fewer costly sprays, higher survivability for beneficial insects, and a chance to come to grips with aflatoxin.

The California and Arizona cotton industries have used PBW eradication program for years. Sterile PBW moths are raised in a rearing facility in Phoenix, Ariz., and shipped to cotton producing areas in the United States. They are dispersed from airplanes.

The basic strategy is to flood the population of native PBW moths with sterile PBW moths at the ratio of 25 to one. The likelihood of two fertile PBW moths mating then becomes very small.

Sterile releases for NOW will start in this spring.

The strategy, proponents say, is “to suppress sterile moth mating of each generation so after a number of years, fertile NOW moths numbers are very minor or even cease to exist, as with PBW.”

The PBW program has been so successful that the Phoenix facility is no longer needed, except to sustain a very small population of PBW in case eradication becomes necessary again in the future.

If the NOW effort works, the plan would house production of sterile NOW moths in part of the Phoenix facility that would be shared with production of sterile PBW moths.

It would likely save some jobs at the facility, Klein said.

Some scientists believe NOW can successfully be reared in massive numbers, sterilized, and distributed by air in the same way the PBW moths are.

Jeff Gibbons, plant and grower relations manager with Setton Pistachio in Terra Bella, is among those on a pistachio industry task force who is a firm believer in the project’s chances for success.

Gibbons said a pioneer in the PBW effort 30 years ago met with the same sort of resistance by some scientists that is facing those looking at the NOW plan.

“This is a no brainer,” he said. “Let’s do it.”

Gibbons said releases of millions of sterile NOW moths would be “another tool in the toolbox to battle such a difficult and aggressive pest.”

He pointed out that the NOW pest is particularly problematic since most pistachios are sold in-shell, and what the pest does to the unseen kernel could end up in a consumer’s mouth literally can leave a bad taste.

“It can bring in mold which tastes awful,” Gibbons said.

Rod Stiefvater, who’s RTS Agribusiness grows pistachios in Fresno, Kern, Madera, and Tulare counties, said there is “nothing like an x-ray to look inside (the shell).”

Also a grower of almonds, Stiefvater said keeping NOW at bay is “hugely expensive, particularly to almonds and pistachio growers.”

Since most almonds and walnuts are not sold in-shell, this means NOW damage is caught well before it winds up in the hands – or mouths – of consumers. Still, the damage cuts yields.

At this point, the pistachio industry is footing the bill for research, about $600,000 raised through a processor assessment of two cents per pound levied by the Administrative Committee for Pistachios.

Some pistachio growers believe almond growers – and possibly walnut growers – would join funding in rearing and releasing moths. Gibbons said releases should cover wide areas since almond, pistachio, and walnut orchards are often contiguous. He added the pest also damages figs and pomegranates.

Millions of sterile NOW moths would be delivered daily on the orchards as soon as moths emerge around March 1 when insect levels are at their lowest.

Release of the sterile moths would continue for several months later than sprays and pheromones in the fall to help reduce over-wintering populations until Oct. 1 or so. Gibbons said the sterile moth program would complement pheromone mating disruption using puffers since the use of the sterile moths is most effective with low populations, and puffers can keep populations low.

Differences between the NOW program and PBW program is that there would be, of course, no “plow down” directive with the NOW releases. NOW has multiple food sources, are better flyers than the PBW, and have different mating habits.

But Gibbons insists, “Let’s try it and see if it works.”

The PBW facility was rearing and distributing 28 million moths per day at cost of less than $1 for a thousand moths.

The NOW program would be aimed more at suppression than eradication, Gibbons said. He added that NOW damage costs pistachio growers around $400 million annually. The hope is that an IPM program using the sterile moths could reduce this cost by 10 percent or more.

Gibbons said the cost of the sterile insect program would cost about $20 million or $15 an acre, “less than the cost of one spray.” Premium and bonus programs offered by processors would help offset those costs.

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