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Monitoring Insecticide Resistance of California Red Scale

The Issue

San Joaquin Valley citrus growers have depended on the relatively cheap and very effective organophosphate and carbamate insecticides for control of California red scale and other pests since the 1950s. Not surprisingly, California red scale began to develop resistance to these two groups of insecticides in the early 1990s.

What Has ANR Done?

Cooperative Extension Integrated Pest Management Specialist Elizabeth Grafton-Cardwell with the University of California, Riverside, documented California red scale resistance to organophosphate (Lorsban and Supracide) and carbamate (Sevin) insecticides throughout the San Joaquin Valley during 1991-1997. She did this by demonstrating that the resistance was due to an increase in esterase enzymes in the resistant scale. She and her colleagues collected scale from many orchards and used a colorimectric test that measures the level of esterase enzymes in individual scale to test them for resistance. More than 300 populations of California red scale in Kern, Tulare, and Fresno counties were tested, with many populations found to be resistant to organophosphates and carbamates. This documentation supported rapid registration of the reduced-risk insect growth regulators (Esteem and Applaud). It also convinced a number of growers to utilize natural enemies (Aphytis wasp releases) for scale control, rather than insecticides. Growers had a sense that resistance was a problem, because they found that they were having to spray more frequently. Documentation of resistance helped to convince them that it was time to use other control tactics.

The Payoff

71% Reduction in Organophosphates and Carbamates Use

Replacement of organophosphate and carbamate insecticides with the insect growth regulators buprofezin (Applaud)and pyriproxifen (Esteem) for scale control and spinosad (Success) for citrus thrips control resulted in a 71 percent reduction in OP and carbamate use (from 1.2 million pounds in 1997 to 0.3 million pounds in 1999) in San Joaquin Valley citrus.


Supporting Unit: UCR Entomology Department

Dr. Elizabeth Grafton-Cardwell
Kearney Agricultural Center
9240 S. Riverbend Ave. Parlier, CA 93648
University of California
Riverside, CA 92521
(559) 646-6591 (Voice)
(559) 646-6593 (Fax)