Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/9/2007
Publication Date: 6/1/2007
Citation: Snodgrass, G.L. 2007. A Laboratory Bioassay for Monitoring Resistance In Tranished Plant Bug Populations to Neonicatinoid Insecticided. National Cotton Council Beltwide Cotton Conference. Available: http://www.cotton.org/beltwide. Interpretive Summary: The tarnished plant bug is a major pest of cotton grown in the mid-South each year. Plant bugs are controlled in cotton exclusively with insecticides. Plant bug populations with resistance to organophosphate, pyrethroid, and carbamate insecticides (the three major classes of insecticides used in their control) high enough to cause control failures have recently been found in the mid-South. The neonicotinoid insecticides represent a new class of insecticides now being used for plant bug control. The main two neoticotinoid insecticides used are Trimax (imidacloprid) and Centric (thiamethoxam). These insecticides are very important to plant bug control in the mid-South since they represent a different insecticide class which can be alternated with the other insecticide classes in the field to help reduce resistance. Because of their importance in plant bug control, a bioassay was developed and used to monitor field populations of plant bugs for resistance to imidacloprid and thiamethoxam. The bioassay is unique in that both insecticides are fed to test populations in honey-water. Previous bioassays developed for resistance monitoring of plant bug populations depended on contact activity of the insecticide. The new bioassay had to be developed because imidicloprid has no contact activity for plant bugs and must be ingested to produce mortality. Monitoring of field populations in 2005 and 2006 produced baseline data which can be used to detect changes in resistance to the two insecticides in future resistance monitoring work
Technical Abstract: A laboratory bioassay was developed for testing tarnished plant bug populations for resistance development to the neonicotinoid insecticides imidacloprid and thiamethoxam. The bioassay allows for the determination of LC50 values by feeding known doses of the insecticides to adult tarnished plant bugs in a honey-water solution. Field populations of plant bugs from several locations in the mid-South were tested with the oral bioassay for resistance to imidacloprid in 2005 and 2006. Resistance to imidacloprid increased 2.46-fold on average in 2006 as compared to 2005. Thiamethoxam was first used in the oral bioassay to test field populations of plant bugs in 2006. The data collected in both years with both insecticides will provide a basis for comparison to determine changes in resistance in future resistance monitoring studies.