Spring 2003 Resistant Pest Management Newsletter Vol. 12, <strong>No.2</strong>INTRODUCTION Insecticide resistance in key insectpests is an important issue for the cotton industry. Twoof the most important cotton pests in the mid-south andsoutheastern United <strong>State</strong>s are the tobacco budworm,Heliothis virescens (F.), and the bollworm,Helicoverpa zea (Boddie). Resistance toorganochlorines, DDT, organophosphates (Sparks1981), and carbamates (Elzen et al. 1992) has beenreported with both species. Resistance in tobaccobudworm populations to pyrethroid insecticides, aswell as isolated field control failures were observed inArkansas (Plapp et al. 1987), Louisiana (Leonard et al.1987), Mississippi (Roush and Luttrell 1987), andTexas (Allen et al. 1987, Plapp et al. 1987) during1986. In response, pyrethroid resistance managementplans were implemented in those states to maintain theeffectiveness of pyrethroids for control of tobaccobudworm (Anonymous 1986). An importantcomponent of these plans was pyrethroid susceptibilitymonitoring for tobacco budworm. Resistance to DDTand organochlorine insecticides has been reported inbollworm (Sparks 1981). In 1998, field control failures(Walker et al. 1998) resulting from pyrethroid-resistantpopulations of bollworm (Brown et al. 1998) werereported in South Carolina. Monitoring of thesusceptibility of bollworm populations in Louisiana topyrethroids was initiated during 1988. To date no fieldcontrol failures of bollworm infestations treated withpyrethroids have been observed in Louisiana.MATERIALS and METHODS Adult vial bioassays (AVT)similar to those described by Plapp et al. (1987, 1990)were used to monitor the susceptibility of fieldcollected tobacco budworm and bollworm moths tocypermethrin. Stock solutions of cypermethrin weredeveloped by dissolving technical grade (98%)insecticide in acetone. Serial dilutions from each stocksolution yielded the desired concentrations. Theinterior surface of 20 ml glass scintillation vials wascoated with cypermethrin by pipetting 0.5 ml of theappropriate solution into vials. These vials were rotatedon a modified hot dog roller (heating elementdisconnected) until all of the acetone had evaporated.Vials were stored in a dark environment until used inbioassays.Male tobacco budworm and bollworm moths werecollected using wire cone traps (Hartstack et al. 1979)baited with synthetic sex pheromone lures (Hendrickset al. 1987) from May through September. Moths werecollected from parishes (tobacco budworm populationssurveyed in 2 to 17 parishes during 1986 to 2002,bollworm populations surveyed in 8 to 20 parishesduring 1988 to 2002) throughout the cotton productionregions of Louisiana (Figure 1). The insecticideconcentrations used in these surveys included10µg/vial cypermethrin for tobacco budworm and5µg/vial cypermethrin for bollworm. Moths wereplaced into insecticide-treated and control (non-treated)vials (one moth/vial) and mortality was determinedafter 24-h of exposure (HAE). Moths were considereddead if they were incapable of sustained flight for ca. 1minute. Data were corrected for control mortality usingAbbott's (1925) formula.RESULTS and DISCUSSION In response to field controlfailures of tobacco budworm with pyrethroids amonitoring program was initiated in Louisiana andcontinued through the present year (Graves et al 1994,Bagwell et al. 2001, Cook et al. 2003). Limited surveys(two parishes) of tobacco budworm susceptibility topyrethroids were conducted during 1986, andconcentrated on fields associated with unsatisfactorycontrol. Mean survival of tobacco budworm mothsfrom Bossier and Tensas parishes was 33% and 41%,respectively (Figure 2). In 1987, more extensivemonitoring efforts were conducted across Louisiana. In1988, only one parish had tobacco budworm survival>30% (East Carroll), while tobacco budworm survivalbetween 11% and 30% was observed in six parishes(Figure 3). During 1990, tobacco budworm survival inCatahoula parish was 51% (Figure 4). Tobaccobudworm survival between 31% and 50% wasobserved in seven parishes. During 1992, tobaccobudworm survival >50% was observed in two parishes(Figure 5). Survival in Madison Parish wasapproximately 60%. Tobacco budworm survivalbetween 31% and 50% was observed in ten parishes.Survival in excess of 50% was not observed in anyparish during 1994 (Figure 6). However, the number ofparishes in which survival between 31% and 50%increased. During 1996, tobacco budworm survivalbetween 31% and 50% was observed in 11 parishes(Figure 7). Survival >50% was observed in twoparishes with 66% tobacco budworm survival observed46
Spring 2003 Resistant Pest Management Newsletter Vol. 12, <strong>No.2</strong>in East Carroll parish. During 1998, tobacco budwormsurvival >50% was observed in seven parishes, with78% survival recorded in Morehouse parish (Figure 8).Also, survival >30% was observed in eight parishes.Tobacco budworm survival >50% was observed inseven parishes during 2000 (Figure 9) representing ca.54% of the parishes in which monitoring wasconducted. Tobacco budworm survival >50% wasobserved in 86% of the parishes during 2002 (Figure10). In Catahoula parish during 2002, 83% survival oftobacco budworm adults exposed to cypermethrin inthe AVT was observed.Pyrethroid susceptibility surveys of Louisianabollworm were initiated during 1988. Bollwormsurvival was 10% was observed in three parishes of16 parishes during 1996 (Figure 15). During 1998,survival >10% was observed in 15 of 20 parishes withsurvival in one parish exceeding 30% (Figure 16).Bollworm survival >10% was recorded in nine parishesduring 2000 (Figure 17). During 2002, bollwormsurvival exceeded 10% in seven of nine parishes and infive parishes survival was >30%, with survival of 42%observed in one parish (Figure 18). Pyrethroidresistance in tobacco budworm gradually increasedfrom 15% statewide during the late 1980's to ca. 40%during the mid 1990's (Figure 19). Resistancemanagement (IRM) plans extended the useful life ofpyrethroids for tobacco budworm control until ca. 1995when they were removed for the Louisiana CooperativeExtension Service Recommendations for control oftobacco budworm in cotton, but they continued to beused for bollworm control. Alternative insecticides fortobacco budworm control became available in 1995, aswell as, Bollgard cotton varieties. During 1995 to 2002,tobacco budworm survival has steadily increased eventhough pyrethroids are not applied to control tobaccobudworm. This continued increase is probably theresult of inadvertent selection pressure from pyrethroidapplications targeting bollworm and other insect pestsof cotton.No field control failures of bollworm treated withpyrethroids have been observed in Louisiana.However, bollworm survival in the AVT has increasedsince 1996 (Figure 20). The highest annual survivalwas observed during the 2002 season (ca. 34%).Presently, pyrethroids are used to control bollworm innon-Bollgard and Bollgard cotton varieties. In addition,these products are also used against other cotton insectpests as well as bollworm in other crop hosts includingcorn, grain sorghum, and soybean.47
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