Eradication not likely
Invasive light brown apple moth in California has dug in.
The light brown apple moth is about a quarter of an inch long.
PHOTO BY R. ANSON EAGLIN, USDA APHIS
State and federal officials, and growers and homeowners, in California have settled in for a long, contentious battle with light brown apple moth, an invasive leaf-rolling insect found there since 2007.
Like other leafrollers, the larvae roll leaves and create webs that often lock leaves and fruit together, and feeding damage on fruit makes it unmarketable.
Officials wrote off the idea of eradicating the insect in 2010, conceding that that cause had been lost, so California growers have a new pest they must contend with. They are controlling it with insecticides and pheromone mating disruption.
The goal now is to keep the insect in California, and many fruit, vegetable, and nursery crop growers must comply with quarantine regulations in order to ship their produce there, said Larry Hawkins, a public affairs official with the Animal and Plant Health Inspection Service in Sacramento.
“There is no eradication program,” Hawkins said. “We long ago abandoned the idea that it could be eradicated. The goal now is to keep host material from moving outside of California unless it has been inspected and cleared.”
Despite the name, the light brown apple moth is not specific to apples. “It would be better called the light brown everything moth,” Hawkins said, since it feeds on more than 2,000 different kinds of plants—deciduous and subtropical fruit trees, berries, ornamentals, forest and shade trees. Besides consuming foliage, they feed directly on fruit such as apples, grapes, peaches, plums, apricots, cherries, and citrus.
On the better news side, the USDA spent nearly three years developing and testing sterile insect release technology for the pest, and it worked well, Hawkins said. By the time it was ready to use, however, the moth had become too firmly entrenched and too widespread.
“It does have promise, but it would not have been quick and it would have been extremely expensive, and we just don’t have the budget to do that,” he said. “USDA does have the information, the technology, the logistics, and the knowledge of how to rear and sterilize large numbers of the moths.” If the moth were to appear elsewhere, the technology could be put to use.
Pest surveys for the moth have been conducted in 21 states, as a precaution. In 2010, the Oregon Department of Agriculture mounted a monitoring program, setting out 1,000 traps, to see if the insect might be in that state. They found one moth, which they determined was a single moth that had somehow hitchhiked into the state and was not an indicator of a breeding population.
Sterile insect release
However, if a hot spot had been found, sterile insect release would have been an ideal solution, Hawkins said. “It’s a numbers game. The idea is to flood an area with so many sterile insects, the odds of a fertile female mating with an fertile male are overwhelmingly small.”
USDA is also willing to work with producer groups if they want to organize and fund a sterile insect release program that would benefit their industry, he said.
USDA has been making strides in sterile insect technology. They have learned they can use X-rays to sterilize insects so they need not use the more expensive gamma ray treatment, although the X-ray process is not yet available on a commercial scale. With some insects, like Mediterranean fruit fly, they have learned how to separate female insects from males, so more sterile males and fewer sterile females are released, improving the effectiveness. They have learned how to rear and feed the insects so they are as strong and healthy as insects in the wild population.
During the study process from 2007 to 2010, APHIS scientist Dr. Greg Simmons worked to develop the sterile insect technology for the light brown apple moth. While the program was not implemented, he reported that advancements were made in mass rearing that increased system production and efficiency allowing stable levels of production to exceed 100,000 moths per week and increased egg production and quality.
USDA is now regularly releasing sterile Mediterranean fruit flies in southern California to prevent Medfly entering the area from other countries. These insects are separated by sex using temperature control. Male pupae survive at a different temperature from female pupae.
The sterile Medfly program covering four counties in southern California has been very effective, Hawkins said. In the years between 1980 and 1993, Medfly cost taxpayers more than $300 million in eradication costs plus lost revenues from lost markets. In the early 1990s, Medfly eradication costs averaged near $30 million per year. The preventive sterile fly release program costs about $12 million a year to operate—a significant savings.
The USDA is also using sterile insect release to suppress pink bollworm, false codling moth, and Caribbean fruit flies.
At a time when eradication was considered possible, the California Department of Food and Agriculture estimated that increased production costs and crop losses could total $133 million per year if light brown apple moth eradication was not successful. Quarantine restrictions and export trade barriers could be devastating.
At the present time, there are both external and internal quarantines in place in California to keep light brown apple moth from leaving the state and from infesting new areas within the state. While the pest has been found at many locations, only a small part of the state was under state interior quarantine—5,741 square miles—as of two years ago. A larger area, about ten counties in the Bay Area and the Central Coast, is under federal order.
The insect is native to Australia, but is now found in New Zealand, Ireland, the United Kingdom, and Hawaii and California. Theoretically, it could survive in the majority of states, especially coast to coast across the southern United States.