Efficacy of Optimum® Intrasect™ Maize Hybrids Against Southern Lepidopteran Pests Matthew W. McKinnon, Jarrod T. Har

1. Efficacy of Optimum® Intrasect™ Maize Hybrids Against Southern Lepidopteran Pests Matthew W. McKinnon, Jarrod T. Hardke, Robert L. Rorie Pioneer Hi-Bred Int’l Inc., Union City, TN Introduction Corn lines expressing Bacillus thuringiensis (Bt) proteins have proven to be effective in reducing economic injury caused by infestations of Lepidopteran insect pests in the southern U.S. However, it remains important to continually develop new technologies and traits to improve efficacy against pests such as corn earworm and southwestern corn borer. Conventional insecticide sprays are not completely effective against corn earworm or southwestern corn borer. Upon hatching on reproductive-stage plants, corn earworm larvae will quickly disperse and enter at the tip of the ear or by feeding through the husk. This behavior by corn earworm provides protection from foliar applications of insecticides. Similarly, southwestern corn borer larvae tunnel into the stalk upon hatching, where they are also protected from insecticide sprays. • The objective of this study was to evaluate the efficacy of Optimum® Intrasect™ hybrids expressing Cry1F and Cry1Ab Bt proteinsagainst natural infestations of Lepidopteran pests in the Mid-south compared to non-Bt hybrids. A + = Figure 2. Corn earworm (CEW) damage to corn ears in non-Bt and Optimum Intrasect hybrids (Area damaged [square cm] / ear evaluated). Stars denote significant differences between the Intrasect hybrid and it’s non-Bt (base) counterpart (P<0.05). • Materials and Methods • Four row plots were planted with an Almaco Seed-Pro planter at a seeding rate of 79,000 plants per ha-1 on 76 cm beds. • Three different corn hybrids were planted, both with and without Optimum Intrasect traits, for six treatments (3 Bt, 3 non-Bt) • 170 kg N per ha-1 were applied at V3-V4 with a knife applicator. • Corn Earworm (CEW) • At R5 the number of larvae in each ear was recorded. • Injury was measured using a mesh grid by the total square centimeters of damage to the primary ear tips and damaged kernels per ear. • Southwestern Corn Borer (SWCB) • Plant stalks were split vertically into two equal halves. • Amount of tunneling by SWCB larvae (in the lower eight internodes upward from the soil) was recorded as total centimeters/plant. Figure 5. Corn earworm larvae showing multiple color variations (A); corn earworm larva on a corn leaf (B); and corn earworm larvae feeding on a non-Bt corn ear tip (C). • Summary and Conclusions • Optimum® Intrasect™ hybrids significantly reduced corn earworm and southwestern corn borer damage compared to similar non-Bt hybrids (P<0.05). • Optimum® Intrasect™ technology suppresses feeding damage caused by corn earworm and southwestern cornborer. • Optimum® Intrasect™ hybrids will result in a reduction in non-Bt refuge requirements compared to previously registered Bt hybrids expressing single proteins, such as YieldGard and Herculex I. • Pyramided Bt proteins into modern corn hybrids has revolutionized insect control strategies throughout the southern region and proves to be the future of insect crop protection. Figure 3. Southwestern corn borer (SWCB) damage to stalks of non-Bt and Optimum Intrasect hybrids (cm of tunneling / stalk). Stars denote significant differences between the Intrasect hybrid and it’s non-Bt (base) counterpart (P<0.05). A • References • Bessin, R. 2003. Bt-Corn: What it is and how it works. Entfact-130. University of Kentucky Cooperative Extension Service. Lexington, KY. • Buntin, G.D. 2010. 2010 Guide to Bt Corn for Georgia. Available at http://www.caes.uga.edu/commodities/fieldcrops/gagrains/documents/guide_tablecombined022010.pdf (Accessed 15 June 2011) University of Georgia Cooperative Extension Service. • Selvi, C., S.V. Krishnamoorthy, and P. Sivasubramanian. A simple and novel bioassay method to evaluate the efficacy of Bt cotton hybrids containing the fusion gene Cry1Ac-1Ab against Spodoptera lituraFabricius. B C A B A B Figure 1. Scoring grid used to count total square cm of damage to corn ears by corn earworm (A). Tunneling by a southwestern corn borer in the base of a corn stalk counted as linear cm of damage (B). Figure 4. Southwestern corn borer larva tunneling in the base of a corn stalk (A), and a larva preparing to overwinter below ground level in the base of a corn plant (B). For additional information contact Matthew W. McKinnon (matwmck2@ut.utm.edu) or Jarrod Hardke (Jarrod.Hardke@Pioneer.com).