Effects of intergenerational host plant alterations on developmental parameters of Spodoptera frugiperda (Lepidoptera: Noctuidae)

The fall armyworm (FAW), Spodoptera frugiperda (Smith), is known as a destructive moth pest of agricultural crops such as corn, rice, and sorghum. Recently, its damage threatens crops in Asian temperate regions due to its high migration ability. Two genetic types of FAW, a corn strain mostly found on corn and a rice strain associated with rice, have been reported. The objective of this study was to evaluate whether migrated corn-collected population of FAW could maintain its population on various seasonal plants including non-preferred Poaceae plants, with special emphasis on Jeju, Korea. Development-related parameters were compared after switching host plants including corn (C), Sudan grass (5), proso millet (M), and rye (R) when rearing FAW. Most developmental parameters showed dynamic changes according to sequential alternation of host plants with the progress of generations. When all R-0 (net reproductive rate) values were scaled by the R-0 in C to C alteration, the scaled values of other alterations were less than "1.0", indicating less fitness than C to C alteration (R-0 value: 0.57 for C to 5, 0.49 for C to M in F3 generation; 0.82 for 5 to 5, 0.65 for 5 to M, and 0.58 for 5 to C in F4 generation, 0.50 for M to M, 0.59 for M to R-0 and 0.83 for M to C in F5 generation). Although our results did not show that S. frugiperda adapted perfectively on new host plants, this pest was able to successfully reproduce up to five generations with non-preferred host plants. Results indicate that winter crops such as rye might be hosts for migrated corn-preferred populations of S. frugiperda during winter after breeding three to four cycles on other host plants before winter if weather condition is allowed for its survival.