Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 8, 1996
Publication Date: N/A
Interpretive Summary: Occasionally, researchers encounter failures in their efforts to screen corn germplasm in the field for resistance to the fall armyworm, a serious lepidopterous pest in the southern U.S. The consequences of these failures are loss of researcher(s) time, funds, seed, and progress. The objective of the present study was to determine the effects of the following three factors: laboratory rearing of test insect, planting date, and plant growth stage at infestation on screening for leaf-feeding resistance in corn to the fall armyworm. Significant differences in leaf-feeding damage scores were found for some comparisons; however, none of those factors appreciably altered the separation of resistant from susceptible genotypes which is the objective of screening. The following precautions may minimize screening failures: 1) periodically cross wild individuals to laboratory reared ones to ensure virulence of insect, 2) rear ample numbers of insects for screening experiments and follow the proper procedures in preparing larvae for field infestations so that healthy, active individuals are present to attack each test plant, and 3) prior to infestation, remove plants from the test plots that are not in the appropriate growth stage.
Technical Abstract: 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 was infested with 30 neonate FAW larvae when the plants of the second planting within each planting period reached the V4 (Tifton) or V8 (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.