Functional Response and Intraspecific Competition in the Fall Armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae).

Abstract

Simple SummaryThe fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is endemic to the Western Hemisphere, where it is particularly damaging to corn, and has become invasive to Africa and Asia in 2016, and 2018, respectively. In January 2019, the FAW was first found in southwest China, and by September 2019 it reached almost all southern Chinese provinces. Since China is the second largest corn producer in the world, it is necessary to study the feeding behavior of the FAW to provide a valuable reference for Chinese corn production and food security. In this study, the functional response and intraspecific competition of the FAW larvae were evaluated under the laboratory conditions. Our study indicates that fifth and sixth instar larvae can cause major host plant damage. Therefore, these should be the focus of any pest management strategy. Intraspecific competition, especially cannibalism impacts the feeding patterns of the FAW larvae and thus needs close attention. Studying the functional response and intraspecific competition could bring tremendous insights into the FAW-host and the FAW-FAW interactions.Functional responses of the fall armyworm (FAW) larvae at each stage, and their intraspecific competition associated with cannibalism, provide insights into developing pest management strategies for the FAW. To help use insecticides more sparingly, the functional response and intraspecific competition of the FAW larvae were evaluated under the laboratory conditions. The results showed that all stages of the FAW larvae displayed a type II functional response to diet. Based on Holling’s disc equation, the search rate (a) and handling time (Th) of sixth instar larvae (a = 0.493; Th = 0.37 min) were the highest, and the shortest of all larval stages, respectively. Intraspecific competition curves fitted the data for fourth to sixth larval stages of the FAW, and the coefficient of intraspecific competition (m) assessed by the intraspecific competition equation were highest for fifth instar larvae (m = 0.48). The present study indicates that 5th and 6th instar larvae can cause the most plant damage (accounted for 88.9% of larval consumption), and these stages should be the focus of any pest management strategy. Intraspecific competition, especially cannibalism, impacts the feeding patterns of the FAW larvae and needs close attention. Understanding the functional response and intraspecific competition of the FAW larvae contributes greatly to practical applications of insecticides, increasing the effectiveness of chemical sprays and decreasing ecological damage.