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 against natural infestations of Lepidopteran pests in the Mid-south region of the U.S.  Trials were planted at multiple locations in Tennessee and Missouri.  Plot size was four rows by 4.6 m in length with four replications arranged in a randomized complete block design.  Corn earworm and southwestern corn borer injury was evaluated on rows one and four of each plot prior to harvest.  Corn earworm feeding injury was determined by recording the number of larvae in each ear, the total square centimeters of corn earworm-attributed injury to the primary ear, and number of damaged kernels per ear using a mesh grid.  To evaluate southwestern corn borer damage, plant stalks were split vertically into two equal halves.  Amount of tunneling (in the lower eight internodes upward from the soil) by southwestern corn borer larvae was recorded as total centimeters per plant.  The results of this study and a summary of the findings will be presented.