Evaluating consumption rates for Helicoverpa zea and Spodoptera frugiperda in Kansas sorghum

The economic injury level (EIL) concept is foundational to any integrated pest management (IPM) program. By combining essential bioeconomic parameters associated with pest densities, host response to injury, and economic losses, the EIL of a given pest population becomes an important tool in making management decisions. The EILs for Helicoverpa zea (corn earworm) and Spodoptera frugiperda (fall armyworm) larvae are of particular consequence to the Kansas grain sorghum, Sorghum bicolor, grower. These insects are annual, late-season pests of grain sorghum panicles and are capable of reducing yields by 25-35 percent if left untreated. An accurate calculation of the EIL for either species is derived in part from the consumption rates of the pest. However, the consumption rates currently used to calculate EILs are out of date in the case of H. zea and undetermined for S. frugiperda. Due to the similarities in their natural history, the consumption rates for these two pest species have thus far been assumed to be the same. Unfortunately, consumption rates for H. zea have not been reevaluated in over 40 years and have never been independently confirmed for S. frugiperda. The objectives of this research were to 1) model current consumption rates for H. zea and S. frugiperda at different densities and 2) validate those models using an independent data set that includes single and mixed-species densities. Field studies were conducted at the Ashland Research Farm near Manhattan, Kansas. Determination of consumption rates as well as their use in updating currents EILs will be discussed.