Journal of Economic Entomology Advance Access published June 21, 2016 Journal of Economic Entomology, 2016, 1–13 doi: 10.1093/jee/tow109 Insecticide Resistance and Resistance Management Research article Impact of Lepidoptera (Crambidae, Noctuidae, and Pyralidae) Pests on Corn Containing Pyramided Bt Traits and a Blended Refuge in the Southern United States F. P. F. Reay-Jones,1 R. T. Bessin,2 M. J. Brewer,3 D. G. Buntin,4 A. L. Catchot,5 D. R. Cook,6 K. L. Flanders,7 D. L. Kerns,8 R. P. Porter,9 D. D. Reisig,10 S. D. Stewart,11 and M. E. Rice12,13 1Department of Agricultural and Environmental Sciences, Pee Dee Research and Education Center, Clemson University, 2200 Pocket Rd., Florence, SC 29506-9727 ([email protected]), 2Department of Entomology, University of Kentucky, S-225 Ag North, Lexington, KY 40546 ([email protected]), 3Texas A&M AgriLife Research & Extension Center, 10345 State Hwy 44, 4 Corpus Christi, TX 78406 ([email protected]), Department of Entomology, UGA-Griffin Campus, 1109 Experiment Downloaded from Street, Griffin, GA 30223 ([email protected]), 5Department of Entomology & Plant Pathology, Mississippi State University, Mississippi State, MS 39762 ([email protected]), 6Delta Research & Extension Center, Mississippi State University, P.O. Box 197, Stoneville, MS 38776 ([email protected]), 7201 Extension Hall, Auburn University, AL 36849 (fl[email protected]), 8LSU AgCenter, Macon Ridge Station, 212A Macon Ridge Rd., Winnsboro, LA 71295 (dkerns@agcen ter.lsu.edu), 9Texas AgriLife Research & Extension Center, Lubbock, TX 79403 ([email protected]), 10Department of Entomology, North Carolina State University, Vernon G. James Research and Extension Center, Plymouth, NC 27962 (ddrei http://jee.oxfordjournals.org/ [email protected]), 11West Tennessee Research and Education Center, 605 Airways Blvd., Jackson, TN 38301 (sdstewart@ut k.edu), 12DuPont Pioneer, P. O. Box 1150, Johnston, IA 50131 ([email protected]), and 13Corresponding author, e-mail: [email protected] Received 2 February 2016; Accepted 27 April 2016 Abstract by guest on June 21, 2016 Blended refuge for transgenic plants expressing Bacillus thuringiensis (Bt) toxins has been approved in the northern United States as a resistance management strategy alternative to a structured refuge. A three-year study (2012–2014) was conducted with 54 trials across nine states in the southern United States to evaluate plant injury from lepidopteran pests of corn and yield in a corn hybrid expressing Cry1F  Cry1Ab  Vip3Aa20 (Pioneer Brand Optimum Leptra) planted as a pure stand and in refuge blends of 5, 10, and 20% in both early and late plantings. Injury by corn earworm, Helicoverpa zea Boddie (Lepidoptera: Noctuidae), and fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), was generally proportional to the percentage of non-Bt corn within each refuge blend. Across locations, ear injury in plots with 100% Cry1F  Cry1Ab  Vip3Aa20 (Optimum Leptra) corn ranged from no injury to a maximum of 0.42 cm2 per ear in Mississippi in 2013. Leaf injury ratings in 100% non-Bt plots in early and late planted trials in 2014 were 86- and 70-fold greater than in 100% Cry1F  Cry1Ab  Vip3Aa20 (Optimum Leptra) plots. Plants in plots with blended refuges had significantly greater leaf injury in 2012 (5, 10, and 20% refuge blends), in the early- planted corn in 2013 (10 and 20% only), and in both early- and late-planted corn in 2014 (20% only) as com- pared with leaf injury in a pure stand of Cry1F  Cry1Ab  Vip3Aa20 (Optimum Leptra) seen during these years. Corn ears in plots with blended refuges also had significantly greater area of kernels injured in 2012 (5, 10, and 20%), in early- and late-planted corn in 2013 (5, 10, and 20%), and in early (10 and 20% only)- and late-planted corn (5, 10, and 20%) in 2014 as compared with ear injury in a pure stand of Cry1F  Cry1Ab  Vip3Aa20 (Optimum Leptra) seen during these years. Infestations of southwestern corn borer, Diatraea grandiosella Dyar (Lepidoptera: Crambidae), were also significantly reduced by Cry1F  Cry1Ab  Vip3Aa20 (Optimum Leptra). Despite these differences in injury, yield averaged across loca- tions varied among refuge blends only in the late-planted trials in 2013, with greater yields in the 0% refuge blend than in the 20% blend; however, when examining yield separately by location, only two of nine loca- tions had higher yields in the 100% Bt plots than in any of the blended refuge plots. As a complement to studying the contribution of blended refuge to delaying resistance, quantifying injury and yield in a range of VC The Authors 2016. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: [email protected] 1 2 Journal of Economic Entomology, 2016, Vol. 0, No. 0 refuge blends is a necessary step to provide management information on the range of lepidopteran pests that occur in the southern United States. Key words: Helicoverpa zea, Spodoptera frugiperda, Bacillus thuringiensis, maize, Optimum Leptra Transgenic corn, Zea mays L., expressing insecticidal Cry proteins the rate of resistance of homozygous individuals is likely to be from Bacillus thuringiensis (Bt) Berliner represented 81% of the initially low and because maintaining pest populations below total corn planted in the United States in 2015 (USDA Economic thresholds is important, the high-dose/refuge strategy has been in- Research Service 2015). The European corn borer, Ostrinia nubilalis strumental in delaying resistance in the United States (Huang et al. (Hu¨bner) (Lepidoptera: Crambidae) was the initial target pests for 2011). Because of issues of grower noncompliance with refuge re- Bt corn in the United States (Koziel et al. 1993). Widespread plant- quirements (Jaffe 2009), a blended refuge, or refuge-in-the-bag, is ing of Bt corn was effective in controlling the European corn borer now used in the Corn Belt (Cullen et al. 2013). However, blended (Rice and Pilcher 2001) and has led to regional reductions in popula- refuges have not been approved in cotton-growing areas of the tions in the Corn Belt (Hutchinson et al. 2010), while being rela- southern United States without a structured block refuge. tively safe to nontarget natural enemies (Pilcher et al. 1997, Naranjo A recent study across 12 states in the southern United States 2009, Carpenter 2011). Although the European corn borer can be summarized the efficacy of a Cry1F  Cry1Ab pyramid with a found in the southern United States, it is generally not considered a blended refuge of a non-Bt hybrid (Reisig et al. 2015). Results key pest of corn (Buntin et al. 2004). Bt traits in corn provide con- showed that injury in the non-Bt plants in the blended refuge did not Downloaded from trol or suppression of a number of other lepidopteran pests that are differ significantly from non-Bt plants in plots with a pure stand of more frequent pests of corn in the southern United States, including non-Bt, suggesting that, with the southern corn insect complex, a corn earworm, Helicoverpa zea Boddie (Noctuidae); fall armyworm, blended non-Bt refuge may not diminish resistance management. A Spodoptera frugiperda (J. E. Smith); southwestern corn borer, concern for the blended refuge concept is larval movement among Diatraea grandiosella Dyar (Crambidae); sugarcane borer, Diatraea non-Bt plants in the refuge and Bt plants, which may accelerate evo- http://jee.oxfordjournals.org/ saccharalis (F.) (Crambidae); and lesser cornstalk borer, lution of resistance (Bates et al. 2005, Goldstein et al. 2010, Elasmopalpus lignosellus (Zeller) (Pyralidae) (Buntin et al. 2004, Wangila et al. 2013). Another concern is that cross-pollination may Reay-Jones and Reisig 2014, Reisig et al. 2015). lead to Bt toxins expressed in blended refuge plants, which may im- Corn earworm eggs are laid on the silks, and young larvae feed pact refuge insects (Yang et al. 2014). In addition, only limited data on the silks before moving to the developing ear. Fall armyworm are available on field efficacy in the southern United States, with can cause defoliation at the whorl stage of corn and also feed on de- Reisig et al. (2015) reporting only one refuge blend (5% non-Bt) veloping kernels in the ear, particularly in late planted corn (Buntin et al. 2004). Early-instar southwestern corn borer and sugarcane without recording yield in trials generally planted within optimum borer can also infest whorl stage corn and cause leaf injury; how- planting dates. Because Lepidopteran insect pests of corn can be by guest on June 21, 2016 ever, later-instar injury can cause more serious injury by tunneling more abundant as the season progresses (Buntin et al. 2004), the ob- into corn stalks, which can stunt or even kill young plants (Hensley jectives of this research were: 1) to evaluate plant injury to a and Arbuthnot 1957, Davis et al. 1972). The use of insecticides is Cry1F  Cry1Ab  Vip3Aa20 (Pioneer Brand Optimum Leptra) hy- particularly challenging in corn because of the difficulty of timing brid with a range of refuge blends and early and late planting dates, applications to control the lepidopteran complex, the lack of com- and 2) to evaluate the impact of injury on yield, which has yet to be plete coverage by aerial application, and the relative concealment of reported in the southern United States with blended refuges. most insects on or within the plant. Corn expressing insecticidal tox- ins is therefore well suited for managing these Lepidoptera pests. Materials and Methods The first commercialized Bt hybrids produced single-gene toxins with events Bt11 (Cry1Ab, Syngenta Seeds, Golden Valley, MN), Locations and Design of Field Experiments MON810 (Cry1Ab, Monsanto Co., St Louis, MO), and TC1507 A three-year study was conducted across 12 southern states to evalu- (Cry1F, Dow AgroSciences, Indianapolis, IN) (Ostlie et al.