Insect colony, planting date, and plant growth stage effects on screening maize for leaf-feeding resistance to fall armyworm (Lepidoptera: Noctuidae)

Field experiments were conducted at Mississippi State, MS and Tifton, GA to determine effects of laboratory insect colony, planting date, and plant growth stage on screening maize, Zea mays L., for leaf-feeding resistance to the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith). The experiments were conducted using a randomized complete block design with treatments in a factorial arrangement with 6 replications. Treatments consisted of 2 insect colonies, an early and a late planting period, 2 plant growth stages, and 4 single cross maize hybrids (2 susceptible and 2 resistant to leaf-feeding by FAW) at each location. Each plant in an experiment was infested with 30 neonate FAW larvae when the plants of the second planting within each planting period reached the V-4 (Tifton) or V-8 (Mississippi State) stage. Each plant was visually scored for leaf damage 7 and 14 days after infestation. Statistical analyses revealed interactions among factors resulting in inferences having to be made using nonmarginal means. Significant differences in rating scores within each factor (insect colony, planting date, and plant growth stage) were found for some comparisons. However, none of these factors appreciably altered our ability to distinguish between resistant and susceptible genotypes which is the objective of screening.