Soft pesticides can be hard on beneficials
Some have sublethal effects on predators and parasites.
Some of the new “soft” pesticides that have been developed in recent years are not so soft on beneficial insects and mites as first supposed, according to Dr. Tom Unruh of Yakima, Washington.
Even when the new pesticides don’t kill predators and parasites outright, they can have detrimental sublethal effects, such as reduced fertility. “I think these products have been registered as kind or gentler, but they really aren’t,” said Unruh, a researcher with the U.S. Department of Agriculture.
Unruh studied the effects of a range of new pesticides on seven natural enemies of key pests in laboratory tests over the course of three years:
Green lacewing, a predator of pear psylla, mealybugs, and moth eggs.
The neonicotynils Actara, Provado, and Assail were acutely toxic to adults and larvae, while Rimon and Success greatly reduced egg hatch.
Mastrus ridibundus, a parasite of codling moth cocoons.
Actara and Success were acutely toxic to the adults at the label rate, and Provado was toxic at a 10 percent rate. Actara and Success reduced the longevity of the female parasites.
Anthocoris nemoralis, a predator of pear psylla and other soft-bodied insects.
High rates of Provado, Assail, Pyramite, and Agri-Mek killed all the female predators. Rimon was not acutely toxic, but none of the eggs laid by Rimon-treated females hatched. Egg hatch was reduced even by low rates of Rimon. Esteem had no acutely toxic or sublethal effects, however.
Colpoclypeus florus, a parasite of leafrollers.
All the neonicotynil pesticides and Pyramite were toxic to adults at field rates, and even a 10 percent rate killed substantial numbers. Rimon killed or sterilized all the parasites exposed to it.
Galendromus occidentalis, the western predatory mite.
Actara and Provado had the greatest impact, but none of the pesticides was extremely toxic.
European earwig, a predator of aphids, pear psylla, and moth eggs.
Success was highly toxic to adults and nymphs. Mortality was often delayed, and this was particularly evident with nymphs exposed to Success and Rimon. In tests in 2004-2005, fertility of females was reduced by 32 percent with Intrepid, 68 percent with Rimon, and 100 percent with Success.
Deraeocoris brevis, a predator of pear psylla and other insects and mites.
Actara, Assail, Calypso, Clutch, Provado, Agri-Mek, Danitol, and Imidan were all acutely toxic to Deraeocoris nymphs.
Actara, Calypso, Clutch, Provado, Danitol, Esteem, Rimon, and Imidan were toxic to eggs.
Rimon, Success, and Agri-Mek reduced the number of eggs laid and the number that hatched.
Reporting to the Washington Tree Fruit Research Commission, which helped fund the studies, Unruh stressed that results of the tests were worst-case scenarios.