Submitted to: Southwest Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2008
Publication Date: 9/1/2008
Citation: Snodgrass, G.L., Gore, J., Abel, C.A., Jackson, R.E. 2008. Predicting Field Control of Tarnished Plant Bug (Heteroptera: Miridae) Populations with Pyrethroid Insecticides by Use of Two Glass-Vial Bioassays. Southwest Entomology. 33:181-190 Interpretive Summary: Tarnished plant bugs are serious pests of cotton in the mid-South controlled mainly with insecticides. Resistance to the pyrethroid class of insecticides developed about twelve years ago and many populations found in the delta of MS and associated areas in north LA and southeastern LA are highly resistant to pyrethroids. The resistance is recessive and some populations in these areas become susceptible to pyrethroids each year, while in other areas such as the hills of MS, western TN, and northeastern AR many populations have never developed resistance. The problem is determining whether or not a population is susceptible before pyrethroids are used to control it. This knowledge could prevent a control failure and yield loss caused by it. The present research reports on a rapid and easily used glass-vial bioassay that determines whether or not a pyrethroid insecticide should be used to control the test population. The bioassay could be easily used by crop consultants or state Cooperative Extension Service personnel to determine the susceptibility of a population to pyrethroid insecticides.
Technical Abstract: Tarnished plant bug, Lygus lineolaris (Palisot de beauvois), populations from 21 locations in the Mississippi River Delta of Arkansas and Mississippi were tested for resistance to permethrin in 2004 and 2005. Each population was tested using permethrin in a discriminating-dose bioassay to determine percent mortality, and with a glass-vial bioassay that used dose-response regression lines to determine LC50 values for permethrin. Results from the two bioassays were compared by regression of percent mortalities with LC50 values. The regression was significant with an R2 value of 0.90 which showed that the two methods of determining resistance were closely correlated. The regression equation had a slope of -0.74 and an intercept of 72.06, which showed that the LC50 value decreased by 7.4 µg/vial for every 10% increase in mortality in the discriminating-dose bioassay. Percent mortality in the discriminating-dose bioassay and LC50 values were related to control of plant bugs in the field using four spray . chamber and one field cage test. Plant bug populations in these tests were not controlled with four different pyrethroids applied at recommended field rates. The results of the tests indicated that either a LC50 value of 24 µg/vial or higher of permethrin, or 60% or lower mortality in the discriminating-dose bioassay with permethrin, could be used to predict field control problems with plant bugs and pyrethroid insecticides in cotton. The discriminating-dose bioassay is a much easier bioassay to use as compared to determining LC50 values using dose-mortality curves. It could be easily used by researchers, consultants, or Cooperative Extension personnel in an insecticide resistance monitoring program for tarnished plant bugs. 1. Delta Research and Extension Center, Mississippi State university, Stoneville, MS 38776