Plant-Insect Ecosystems
10-Minute Paper
Sandipa Gautam
UCCE IPM Advisor
University of California
Exeter, California
Elizabeth Grafton-Cardwell
IPM Specialist
University of California
Exeter, California
Sanjeev Dhungana
University of California Statewide IPM Operations
Exeter, California
California is a leading producer of fresh citrus in the United State contributing $7 billion to the U.S. economy. The presence of rind defects such as that caused by citrus thrips (Scirtothrips citri) decreases the marketability of the fruit. As such growers in the San Joaquin Valley California make multiple insecticide applications per season to reduce rind scarring caused by feeding. Repeated use of synthetic insecticide coupled with multiple generations of thrips in a season has led to resistance development to several insecticides, making citrus thrips management challenging for growers. The Munger cell laboratory bioassay technique was adopted to examine resistance to Delegate WG (spinetoram) in field populations collected from San Joaquin Valley from 2017 to 2022. Two concentrations (1 and 10 ppm) of Delegate WG were prepared to dip leaves and measure the resistance. The numbers of alive and dead thrips were counted after 48 hours of insecticide exposure. The overall trend from 2017-2022 showed a higher percentage of thrips surviving 1 ppm discriminating dose. More importantly, in later years, a higher percentage of the population survived 10 ppm, indicating field rates of Delegate WG may not control thrips effectively. Well-timed and suitable treatment with a rotation of available active ingredients reduces the likelihood of resistance development and consequently reduces the number of applications. Implications of the results and recommendations for managing citrus thrips resistance are discussed.