INSECTICIDE RESISTANCE AND RESISTANCE MANAGEMENT Concentration–Response and Residual Activity of Insecticides to Control Herpetogramma phaeopteralis (Lepidoptera: Crambidae) in St. Augustinegrass 1 2 1 NASTARAN TOFANGSAZI, RON H. CHERRY, RICHARD C. BEESON, JR., AND STEVEN P. ARTHURS1,3 Downloaded from https://academic.oup.com/jee/article/108/2/730/781136 by guest on 28 September 2021 J. Econ. Entomol. 108(2): 730–735 (2015); DOI: 10.1093/jee/tov012 ABSTRACT Tropical sod webworm, Herpetogramma phaeopteralis Guene´e, is an important pest of warm-season turfgrass in the Gulf Coast states of the United States, the Caribbean Islands, and Central America. Current control recommendations rely on topical application of insecticides against caterpil- lars. The objective of this study was to generate resistance baseline data of H. phaeopteralis to six insecti- cide classes. Residual activity of clothianidin, chlorantraniliprole, and bifenthrin was also compared under field conditions in Central Florida. Chlorantraniliprole was the most toxic compound tested (LC50 value of 4.5 ppm), followed by acephate (8.6 ppm), spinosad (31.1 ppm), clothianidin (46.6 ppm), bifen- thrin (283 ppm) and Bacillus thuringiensis kurstaki, (342 ppm). In field tests, all compounds at label rates were effective (94% mortality of larvae exposed to fresh residues). However, a more rapid decline in ac- tivity of clothianidin and bifenthrin was observed compared with chlorantraniliprole. Clothianidin had no statistically detectable activity after 4 wk post-application in spring and the fall, and bifenthrin had no detectable activity after 3 wk in the spring and the fall. However, chlorantraniliprole maintained signifi- cant activity (84% mortality) compared with other treatments throughout the 5-wk study period. This study provides new information regarding the relative toxicities and persistence of current insecticides used for H. phaeopteralis and other turfgrass caterpillars. KEY WORDS median lethal concentration, resistance baseline, chlorantraniliprole, turf St. Augustinegrass, Stenotaphrum secundatum (Walter) fall (September through November; Cherry and Wilson Kuntze, and bermudagrass, Cynodon spp., are the 2005). Populations decline over the winter and increase most widely used turfgrasses in Florida lawns and golf slightly beginning in spring (March through May). In courses, respectively (Trenholm and Unruh 2004). the more northern regions of Florida, peak of flight ac- Tropical sod webworm, Herpetogramma phaeopteralis tivity was reported in October and November (Kerr (Guene´e), is a serious pest of both grasses (Kerr 1955). 1955). Females lay eggs on grass blades and eggs hatch All other major warm-season turfgrass including centi- within 4 d at 25C(Tofangsazi et al. 2012). Young lar- pedegrass [Eremochloa ophiuroides (Munro.) Hackel], vae (first through fourth instars) feed on adaxial side of seashore paspalum (Paspalum vaginitium Swartz), car- grass blades and their injury is often overlooked (Kerr petgrass (Axonopus spp.), zoysiagrass (Zoysia japonica 1955). Older larvae (fifth and sixth instars) remove en- Steudel and Zoysia matrella L.), and bahiagrass (Paspa- tire grass blades causing brownish mown patches lum notatum Fluegge´) are also subject to infestation by that allow weed ingress (N. Tofangsazi, personal H. phaeopteralis (Reinert 1983). H. phaeopteralis oc- observations). curs from South Carolina to Florida, west to Texas in Successful turf pest management requires incorpo- North America, the Caribbean, and south through rating insecticides because of the aesthetic nature of Central America (Brandenburg and Freeman 2012; turfgrass and high standards demanded by users, Heppner 2003). growers, and turfgrass managers (Brandenburg and In southern Florida, H. phaeopteralis adults are ac- Freeman 2012, Held and Potter 2012). Lawn caterpil- tive year-round, with significantly higher numbers in lars including H. phaeopteralis larvae have traditionally been managed with broad-spectrum insecticides; those used historically on Florida lawns include carbaryl, chlorpyrifos, diazinon, ethoprop, methomyl, trichlorfon, pirimiphos-methyl, isazofos, isofenphos, fonofos, and 1 Department of Entomology and Nematology, Mid Florida Research toxaphene (Reinert 1983). Reinert, in 1973 and 1983, and Education Center, University of Florida, Apopka, FL 32703. evaluated carbaryl, chlorpyrifos, bendiocarb, and etho- 2 Department of Entomology and Nematology, Everglades Research and Education Center, University of Florida, Belle Glade, FL 33430. prop against H. phaeopteralis larvae. However, to date, 3 Corresponding author, e-mail: [email protected]. these insecticides have been canceled or restricted VC The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: [email protected] April 2015 TOFANGSAZI ET AL.: INSECTICIDE EFFICACY AGAINST H. phaeopteralis 731 following the Food Quality Protection Act (FQPA) of (164.9, 82.5, 41.2, 20.6, and 10.3 ppm), chlorantranili- 1996. Information is not available on toxicity of newer prole (35.9, 17.9, 8.9, 4.5, and 2.2 ppm), B. thuringien- insecticides and formulations to control H. phaeoptera- sis (1327, 663, 333, 166, and 83 ppm), bifenthrin lis larvae. (706.5, 353.2, 176.2, 88.3, and 44.1 ppm), spinosad Currently, at least 11 turfgrass pests have developed (97.7, 48.8, 24.4, 12.2, and 6.1 ppm), and acephate insecticide resistance in the United States, although fall (37.9, 7.6, 3.8, 2.5, and 1.9 ppm) that were used to armyworm, Spodoptera frugiperda (J.E. Smith), is the establish concentration–response curves. For each only lepidopteran turf pest with documented resistance tested insecticide, 500 ml per serial dilution (plus to organophosphate, carbamate, and pyrethroid com- 0.5ml/liter of Tween 80% for B. thuringiensis contact pounds (Silcox and Vittum 2012). The ability of H. insecticides, spinosad and bifenthrin, and water con- phaeopteralis to develop resistance is of concern be- trols) were sprayed on 20-cm-diameter pots of cause of its multiple generations per year and overlap- Palmetto St. Augustinegrass. Applications were made Downloaded from https://academic.oup.com/jee/article/108/2/730/781136 by guest on 28 September 2021 ping life stages, especially in Florida, where lawn and with a spray booth (DeVries Research, Hollandale, sod farms are treated with insecticides 6 to 12 times an- MN) fitted with fan nozzle, calibrated to deliver the nually (unpublished data). It is thus important to plan equivalent of 2,037 liter/ha (218 gallon/A) at a pressure and implement insecticide resistance management of 207 kPa. strategies for controlling this pest before field control After 24 h, St. Augustinegrass stolons containing failure is encountered. fresh shoots were cut from the pots and placed individ- Resistance monitoring programs require establishing ually into Petri dishes (8.5 cm in diameter) containing resistance baselines and survey for statistically signifi- 6 ml of water agar covered with filter paper to maintain cant shifts in lethal concentrations values (LC50; Cook humidity. Five replicates were set up for each treat- et al. 2004). These are normally established through ment, with four medium-sized H. phaeopteralis placed laboratory bioassays, which should be initiated when inside each Petri dish. All Petri dishes were kept in an frequency of resistant individual are low or before a incubator at 25 6 1C, 70% relative humidity, and a product is widely used to develop historical reference photoperiod of 14:10 (L: D) h. Dead individuals values (Cook et al. 2004, Hardke et al. 2011). In addi- tion, environmental factors such as ultraviolet (UV) (defined as no response to prodding) and moribund light, temperature, rainfall, plant metabolism, and mi- individuals (defined by uncontrolled twitching croorganisms influence patterns and rates of degrada- and other abnormal movements) were reported after tion under field environments (de Urzedo et al. 2007, 72 h. Initial experiments indicated that moribund larvae Hulbert et al. 2011). Understanding residual properties after this time did not recover from insecticide expo- of insecticides under field conditions might prevent un- sure. Thus, moribund individuals were considered necessary insecticide reapplication and associated costs. dead for analyses. The bioassay was replicated three Thus, objectives of this study were to estimate resis- times (i.e., 60 larvae per treatment concentration). tance baselines and lethal activity range of insecticide Larval mortality was pooled for a given concentrations classes, and to determine relative effectiveness of and subjected to analysis of variance (PROC PROBIT a field-aged residue of these insecticides against on log10 concentrations to estimate LC50 and LC90 val- H. phaeopteralis larvae. ues, SAS Institute 2012, Cary, NC). Significant differ- ences were based on nonoverlapping 95% CIs (Finney 1971). Materials and Methods Field Studies. Experiments were conducted to measure residual control of insecticides with different Insects and Insecticides. Medium-sized (third and modes of action, i.e., chlorantraniliprole, clothianidin, fourth instar) H. phaeopteralis used in the experiments and bifenthrin, against medium-sized (third and fourth were obtained from a colony maintained since 2011 on instar) H. phaeopteralis. Experiments were conducted potted St. Augustinegrass ‘Palmetto’ inside greenhouse on ‘Floratam’ St. Augustinegrass plots maintained