Comparison of infestation rates of fall armyworm (Lepidoptera: Noctuidae) neonates for maize resistance screening

An economically important global maize pest, fall armyworm (Spodoptera frugiperda (J.E. Smith)), feed on all above-ground portions of maize plants, primarily the whorl tissues. One of our research unit missions is to identify and develop maize germplasm with resistance to fall armyworm. One method to measure resistance in maize to fall armyworm is visual rating of leaf-feeding damage after infestation with neonates into the whorl. The objective of this study was to compare leaf-feeding damage ratings after infestation with different rates of fall armyworm neonates. The ultimate goal was to select the smallest infestation rate which could give the same damage effect on maize leaves as the larger infestation rates. Four susceptible and 7 resistant maize germplasm lines were planted in replicated experiments with a split plot arrangement in the field in the summer of 2023 and 2024. Plants were infested with fall armyworm at 10-, 20-, 30-, 40-, and 50-neonate infestation rates (treatment). Leaf-feeding damage was scored 14 d after infestation. In general, 10-neonates infestation rate exhibited less damage in comparison to the higher infestation rates indicating much less pressure from fall armyworm to exhibit resistance in maize regardless of the lines. Overall results showed that 20-, 30-, and 40-neonate infestation rates did not differ in the leaf-feeding damage scores among each other. These rates were able to clearly distinguish the damage between susceptible and resistant lines; hence, 20-neonate rate could be used as the standard infestation rate for future infestation in the maize resistance research program.