Fall Armyworm May Have a Persistent Presence as Oviposition Lingers in August

During July of 2021, fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) caused serious damage in soybeans and forages in Central and Western Kentucky. Fall armyworm is a polyphagous pest that feeds on many plant species of the Poaceae (grasses, including rice, maize, sorghum, wheat, oats, pasture grass), Asteraceae (marigold, pyrethrum, lettuce, sunflower), Fabaceae (peanut, chickpea, soybean), and Brassicaceae (broccoli, cabbage, field mustard).

Armyworm trap captures decreased in August (Table 1) aqfter it reached its peak at the end of July. However, these traps only capture male specimens (attracted by a synthetic sex pheromone mimic); traps indicate the movement or migration of fall armyworm males. In contrast, mated females might have lagged behind and still be present laying egg masses in Western and Central Kentucky (Figure 1).

Table 1. Numbers of fall armyworm males trapped on pheromone-based traps in Princeton and Lexington from July 3 to August 13, 2021.

During the past 2 weeks, we have been observing egg masses in pastures, soybeans, corn, and sunflowers; as well as on other structures, such as screens, walls, tree trunks, cardboard-based insect traps, and on liners and bottom parts of plastic traps (Figure 2). It is well known that fall armyworms can lay eggs on other structures than plant material. The latter can be observed in no-choice test bioassays where fall armyworms laid egg masses on walls of cages rather than on plant material (Figure 2).

Figure 1. Egg masses and emerging larvae of the fall armyworm on (A) a wall, (B) trap liner and (C) trap, (D) sunflower, and (E) bottom of plastic insect trap observed in August 2021. (Photos: Raul Villanueva, UK)

Figure 2. Total number of eggs and egg masses (mean ± SD, min.-max. range) of the fall armyworm, Spodoptera frugiperda recorded under a no-choice experiment arena and using (a) tomato, (b) maize, (c) tomato sprayed with maize extract, and (d) maize sprayed with tomato extract. (Reproduced from Sotelo-Cardona, et al. Sci Rep 11, 15885 (2021); https://doi.org/10.1038/s41598-021-95399-4)

Farmers, scouting agents, crop consultants, and county Extension agents should be aware of this situation and be monitoring for eggs and fall armyworm larvae in order to prevent damage to field crops and pastures.

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By Raul T. Villanueva, Entomology Extension Specialist, and Zenaida Viloria, Entomology Research Analyst

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