Effects of soil applied imidacloprid on behavior of Plannococcus ficus

Authors: Sisterson, Mark; Uchima, Sean

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: The vine mealybug is the most important pest of grapevine in California. Because vine mealybug is protected from contact insecticides by residing under the bark of grapevines, systemic insecticides are a popular choice for control. The systemic insecticide, imidacloprid, has been one of the primary products used to control sap feeding insects in vineyards for nearly two decades. ARS researchers in Parlier, CA conducted a series of studies to determine effects of soil applied imidacloprid on vine mealybug survival and behavior on grapevine. Low concentrations of imidacloprid were effective against crawlers (newly hatched eggs). However, mature females survived all imidacloprid concentrations tested. Results suggest the mature mealybug females cease feeding in response to stress and mobilize stored energetic resources to produce eggs.

Technical Abstract: The vine mealybug threatens grapevine production worldwide. Mealybugs impact grape production by reducing vine vigor, promoting growth of sooty molds, and by transmitting viruses. Because mealybugs are protected from contact insecticides by residing under bark, systemic insecticides including the neonicotinoid imidacloprid are popular choices for control. To better understand response of mealybugs to vines treated with imidacloprid, a series of no-choice and choice tests were conducted. No-choice tests conducted with crawlers, indicated that crawlers could initially establish on plants treated at all imidacloprid concentrations tested (0, 1, 10, and 100 ug[AI]/ml). While all mealybugs on plants treated with the two highest concentrations of imidacloprid died prior to maturation, mealybugs did complete development and produced viable offspring on plants treated with the lowest concentration (1 ug[AI]/ml). To evaluate effects of imidacloprid on larger mealybugs, no choice tests were conducted using mealybug cohorts aged 3- or 4-weeks. A single mealybug was allowed to establish on an untreated grapevine. After the mealybug was established, the vine was treated with one of four concentrations of soil applied imidacloprid and response evaluated after 6-days. Treatment concentration did not affect mealybug survival, although mealybugs on plants treated at the highest concentrations were more likely to leave plants. While there was a minor reduction in egg production for females exposed to the highest concentrations of imidacloprid, females exposed to treated plants still produced eggs. Subsequent choice tests using mealybugs from cohorts aged 3- and 4-weeks indicated no preference for treated versus untreated plants. Results indicated that crawlers are more susceptible to imidacloprid than mature mealybugs. Because imidacloprid must be consumed to kill insects, mealybugs appear to respond to treatment by ceasing to feed and mobilizing stored energetic resources to produce eggs.