A laboratory bioassay for monitoring resistance in tarnished plant bug populations to neonicotinoid insecticides

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.