In an attempt to curb an invasive moth infestation, the California Department of Food and Agriculture (CDFA) will release stingerless wasps to organically control the population and protect crops in Sacramento and San Luis Obispo counties.
The light brown apple moth (LBAM), originating in Australia but now also widespread throughout the United Kingdom, New Zealand, Ireland and New Caledonia, was first reported in California in 2007. According to a United States Department of Agriculture description of the LBAM, the species affects “over 1,000 plant species and more than 250 fruits and vegetables,” including cypress, redwood and oak trees, as well as grapes, nectarines and cherries.
Cal Poly horticulture and crop science assistant professor Michael Costello, said due to other pests that already affect grapes and fruits in California, the state worries about the effect of this species of moth.
“We already have two grape moth pests that are pretty closely related,” Costello said. “If it were just a grape thing, we could just deal with it. But (because) it feeds on lots of different fruit plants, we get a little worried.”
Steve Lyle, the director of public affairs for CDFA, said “the objective of all CDFA pest management programs is to stop the pest before it causes damage.”
In order to do this, the release of the wasps will be part of an integrated pest management (IPM) program, intended to not only suppress the effects of invasive pests, but also, suppress environmental effects.
Assistant professor David Headrick, who also works in the horticulture and crop science department and helped advise the secretary of the CDFA “regarding appropriate measures for (LBAM) eradication (and) control,” said the tiny, microscopic wasp, called a Trichogramma platneri, “seeks out” the eggs of LBAM and “insert(s its) own egg;” thus, the wasps help kill the moths biologically instead of using pesticides. Headrick said the wasp also is indigenous to California so it is already incorporated into the ecosystem.
“If we can deploy a native wasp to attack the LBAM populations, and hopefully, maintain them at non-economic levels, then to me that is a reasonable, responsible and environmentally-appropriate approach,” Headrick said. “Invasive species impact all of us and it’s important that we evaluate each one and make good decisions about what to do. Not doing anything is not a good approach.”
Costello said, however, that the wasp does not only kill LBAM, it also kills other species of moths and butterflies. In addition, he said if the CDFA wanted to “eradicate” the LBAM population, a large amount of wasps would need to be released, and even that would not kill the whole population.
“Even if (the wasps) were just looking for light brown apple moths, which they’re not, 90 percent would be the absolute best,” Costello said. “They are not going to find them all. And a lot of what they are going to find are (other moth species), not light brown apple moths.”
Yet, Costello said releasing more wasps into the ecosystem would not significantly affect other moth and butterfly populations.
Lyle also said the wasps would not be released in areas with endangered butterflies.
Using the wasps to curb the LBAM population comes after an effort in 2007 using pheromones in Monterey and Santa Cruz counties. After spraying number 487, people reportedly complained that they had become ill due to the pheromones. Yet only 79 sought medical attention and only 45 of those had a Pesticide Illness Report filed, which doctors must file if they feel an illness is caused by pesticides.
The Office of Environmental Health Hazard Assessment, the California Department of Public Health and the state Department of Pesticide Regulation concluded in 2008 that there was not enough evidence to say the pheromones caused illness.
Costello said the pheromones are meant to only affect insects, as opposed to pesticides that affect both insects and humans. He said they should not make people sick, but he could not say with certainty that a small amount of people would be affected.
Headrick said the problem with the 2007 eradication attempt was the application, not the technology.
“The pheromone technology works well, the application method was a disaster,” Headrick said. “That’s water under the bridge, but it will be a long time before the citizens of the state will have any trust in the CDFA’s plans for invasive species eradication/control. Pheromone technologies are safely used day in and day out in a variety of cropping systems and effectively reduce pest populations without the use of pesticides.”
Additionally, according to a 2010 state environmental report, LBAMs have not caused any significant damages to crops. However, Lyle said they did cause damage to berries in Santa Cruz County. Costello said it may take time for the moths to become a significant problem. Yet, he felt releasing the wasps would help slow the growth of the LBAM population until perhaps a natural enemy that only attacks LBAM can be established. After that, Costello said at some point the growers will have to tackle the problem on their own, like with other pests.
“If (the state) can slow it, (and) help the researchers bring in a new natural enemy, that’s really going to (be the most effective method),” Costello said. “At some point they’ll say, we’re not involved anymore, we have to move on to something else.”