The resistance status of Tetranychus urticae Koch and Lygus hesperus Knight sourced from California strawberry fields was evaluated in laboratory bioassay experiments. Adult female T. urticae sourced from a miticide naïve population were exposed to a range of miticide active ingredient concentrations mixed with acetone in contact bioassay experiments. LC50 concentrations for the active ingredients fenpyroximate, abamectin, bifenazate, and spiromesifen as well as LC90 concentrations for the active ingredients fenpyroximate, abamectin, and bifenazate were derived from this susceptible population. A total of ten field populations of T. urticae, five from the Santa Maria growing region and five from the Ventura/Oxnard growing region, were exposed to these concentrations and mortality response was compared with the susceptible population to determine the resistance status of T. urticae on a per-field basis.
Resistance detection occurred less often in the LC50 concentration groups compared to their respective LC90 concentrations. Resistance to the LC50 concentration of spiromesifen could not be detected in any field population. Resistance to the LC90 concentrations of fenpyroximate and abamectin was detected in three field populations from Santa Maria and four populations from Ventura/Oxnard. Resistance to the LC90 concentration of bifenazate was detected in three populations from Ventura/Oxnard and in no populations from Santa Maria.
Lygus hesperus were exposed to formulated products registered in California strawberries after being separated into three groups based on life stage. Instars one through three were considered small, instars four and five were considered large, and winged individuals were considered adults. The small and large groups were exposed to the maximum field labeled rate of Rimon® (a.i. = novaluron). Adults were exposed to the maximum field labeled rate of Actara®, Brigade®, and Sivanto®, the active ingredients of which are thiamethoxam, bifenthrin, and flupyradifurone respectively. A total of 14 field populations were screened for resistance, six collected from the Santa Maria growing region in 2021, and eight collected in 2022, five of which came from the Santa Maria region, and three from the Salinas/Watsonville region. Resistance was detected by comparing the mortality response of an insecticide naïve population of L. hesperus and field collected populations in residual laboratory bioassay experiments. Resistance to Rimon® in the small group was effectively detected in all populations in 2021 and 2022. Resistance to Rimon® in the large group was detected in four populations in 2021 and five populations in 2022. Resistance to Actara® and Brigade® was effectively detected in all populations in 2021 and 2022. Resistance to Sivanto® was effectively detected in four populations in 2021 and two of three populations in 2022. A full submersion assay was utilized for the second half of Sivanto® trials in 2022 since mortality response of the susceptible population was low in the residual group. Five of five populations tested with the modified assay were considered effectively resistant.
| Identifer | oai:union.ndltd.org:CALPOLY/oai:digitalcommons.calpoly.edu:theses-4264 |
| Date | 01 June 2023 |
| Creators | Jensen, Kiley William |
| Publisher | DigitalCommons@CalPoly |
| Source Sets | California Polytechnic State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Master's Theses |
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