Vol.12_No.2 - Pesticide Alternatives Lab - Michigan State University

Spring 2003 Resistant Pest Management Newsletter Vol. 12, No.2Van Rie, J., Jansens, S., Hofte, H., Degheele, D., Van Mellaert, H., 1989.Specificity of Bacillus thuringiensis d-endotoxins: importance ofspecific receptors on the brush border membrane of the midgut oftarget insects. Eur. J. Biochem. 186, 239-247.Juan L. Jurat-FuentesDepartment of EntomologyUniversity of GeorgiaAthens, GA-30602USAFred L. GouldDepartment of EntomologyNorth Carolina State UniversityRaleigh, NC-27607USAMichael J. AdangDepartments of Entomology andBiochemistry and Molecular BiologyUniversity of GeorgiaAthens, GA-30602USAMonitoring Onion Thrips Resistance to Pyrethroids in New YorkThe onion thrips, Thrips tabaci Lindeman, is a pestof onions and related Allium species, as well as dozensof other plant families, throughout the world. Themajor control strategy for onion thrips on onions is thefrequent use of insecticides and growers may applytreatments weekly, especially in hot, dry years. There isconcern that such intensive treatments may result in thedevelopment of resistance. The results reported in thispaper include studying the susceptibility of onion thripspopulations in New York to l-Cyhalothrin (Warrior T)in 2001 and in 2002 using a newly developed assaysystem and conducting a simulated field test tocompare the results from the laboratory assays to fieldperformance.MATERIALS and METHODSEvaluating Onion Thrips Populations against Warrior:We used the Thrips Insecticide Bioassay System(TIBS) developed by Rueda and Shelton (2003). Thissystem allows thrips to be collected directly from onionplants into a 0.5 ml microcentrifuge tube previouslytreated with an insecticide. Thrips mortality is assessedat 24 h with the help of a dissecting stereoscope andthen data are analyzed to calculate the meanlethal concentration that would kill 50% of thepopulation (LC50). During the 2001 growingseason, thrips populations were collected from 16different sites encompassing the major growingareas of New York. In 2002, populations werecollected from 10 different sites at two differenttime periods (mid-season and late-season). Thereason for the two collections was to determinewhether there are changes in susceptibility overtime. For each of these collections we only testedthe populations against a single dose, the fielddose of 100 ppm. This decision was based onevidence collected in 2001 that fields in which itwas difficult to control thrips with Warrior hadLC50 values > 100 ppm.Determine the Relationship between Lab Assaysand Simulated Field Performance:From our collections of onion thrips in 2002,we selected four populations that varied significantly intheir susceptibility to Warrior, based on our laboratoryassay using TIBS. We introduced these populationsonto onion plants treated with the field rate of Warriorusing a carbon dioxide backpack sprayer. Afterspraying, the insecticide was allowed to dry for 24hours and then 20 thrips larvae were introduced into acage containing a single plant. Thrips were allowed tofeed and then mortality was assessed after 5 days.There were eight cages (replicates) for each of the fourpopulations of thrips used in this study.RESULTS and DISCUSSIONEvaluating Onion Thrips Populations against Warrior:Of the 16 populations examined in 2001, sevenhad LC50 values greater than the field dose of 100 ppmindicating a potential for poor field performance(Figure 1). In the figure the fields are grouped byregion (e.g. Orange County denoted by OR 1-3)) andthere was considerable variation within each regionwith some fields having populations of thrips withLC50 values much higher or lower than the field rateof 100 ppm. This indicates that individual grower44