CLOSE TO HOME: Wasting millions combating the apple moth


Published: Monday, July 6, 2009 at 3:00 a.m.

Now that Friday’s public comment deadline has passed, state and federal agriculture agencies are one step closer to a test-release of tens of thousands of sterile moths over three square-miles of vineyards on the Napa-Sonoma county border in the latest stage of a scientifically invalid and futile effort to eradicate the light brown apple moth.

The pest-management strategy being tested, known as sterile insect technique, is based on the seemingly plausible idea that if one raises millions of male moths in a laboratory, sterilizes them with radiation and then sets them free, they will mate with wild female moths at rates sufficient to cause extinction. But, in fact, this technique has failed to eradicate most of the pests on which it has been tested in the past, and the design of this particular test is deeply flawed.

That the sterile insect technique will be ineffective in eradicating the apple moth either alone or in combination with other tools is supported by the history of its failure against other moth pests as well as by the biological characteristics of moths in general and the apple moth in particular.

First, of the 12 species of moths on which sterile insect research has been conducted, some level of control was attained in only three and unequivocal eradication achieved in none.

Second, because radiation resistance in moths is much greater than in many other insect groups, massive doses are usually required to achieve complete male sterility. These high doses severely reduce the ability of males to compete for mates and, much worse, often prevent sperm transfer, with the result that females who mate with sterile moths continue to seek mates.

Third, the light brown apple moth is one of the worst candidates for use of the sterile insect technique for eradication because of its small size, fragility, continuous breeding, multiple matings, rearing difficulties, ability to prosper in protected environments (e.g., screened porches), distribution over at least 17 California counties and 250-plant host range.

In reviewing the U.S. Department of Agriculture’s May 2009 environmental assessment of the apple moth sterile insect test, we identified three design flaws that will render the test results scientifically invalid:

• No measurement parameters are specified (e.g., rates of induced infertility in wild females), and no statistical criteria are established for distinguishing changes in apple moth populations attributable to the released sterile moths vs. random chance or normal population ebb-and-flow.

• No control plots or treatment replications are included; controls and repeatable results are cornerstones of experimental science.

• The likely pitfalls that we know well from other insect eradication programs of the past are not addressed. For example, the study design does not address how to distinguish between causes of population reduction due to the released sterile moths vs. those due to high predation levels. The experimental design also ignores the overarching question of how to use the results of such a short-term investigation involving a small, isolated area to inform a policy concerned with eradicating a pest embedded in an ecological mosaic that constitutes a quarter of our state, in which nearly a third of Californians reside.

It is puzzling why state and federal agriculture agencies have not first laid to rest the many serious doubts about the potential effectiveness of the sterile insect technique as an apple moth eradication tool before attempting to move forward with a study whose results could not possibly stand up to any serious scientific or legal challenge.

Because the government’s light brown apple moth policies involve thousands of square miles, millions of people and tens of millions of dollars, they surely must be based on far more persuasive arguments supporting the sterile insect technique’s potential efficacy than have been put forth thus far, be supported by studies that adhere to at least basic scientific standards and be vetted by independent, objective scientists willing to openly voice to policymakers their honest, dispassionate opinions based on hard facts.

This standard should apply not just to this latest ill-conceived apple moth eradication strategy, the sterile insect technique (which will cost an estimated $10 million a year by itself after the construction of a $35 million rearing facility in Moss Landing) but to the entire $90-plus million light brown apple moth program and the poorly substantiated conclusions that the moth is a dangerous pest and that it can be eradicated.

James R. Carey is a professor in the U.C. Davis Department of Entomology. Daniel Harder is executive director of the arboretum at U.C. Santa Cruz.