Fallet et al - Entomopathogenic nematodes as an effective and sustainable alternative to control the fall armyworm in Africa - Dataset and R Script

We tested in field trials in Rwanda in 2022 the efficacy of entomopathogenic nematodes (EPN) to control the fall armyworm (Spodoptera frugiperda Smith; FAW) over a complete growing season of maize. For an exhaustive description of the method, please see the publication: Fallet et al., 2024. PNAS Nexus. DOI: https://doi.org/10.1093/pnasnexus/pgae122

Briefly, the trials were conducted in six fields each containing 20 plots. In each field, five plots were attributed to one of the following treatments (n = 30 plots per treatment in total):

Untreated control (negative control)

EPN formulated in a Surfactant-Polymer-Formulation (SPF; e-nema GmbH, Schwentinental, Germany)

EPN formulated in a carboxymethyl cellulose gel (Gel; Fallet et al., 2022. Biol. Control. DOI: https://doi.org/10.1016/j.biocontrol.2022.105086

Cypermethrin (positive control; pyrethroid contact insecticide)

Treatments were applied into the whorl of every plant within a plot as a 2ml spot application, starting when >30% of plants were infested with FAW. Treatments were re-applied every two weeks until the maize flowers emerged. In total, treatments were applied four times in fields I, II, II and IV, and three times in fields V and VI.

Data recorded

Whorl damage:Whorl damage was visually assessed seven- and fourteen-days post after the first-, second- and third-treatments on 40 plants per plot using the Davis whorl damage scale (Davis et al., 1992) as described in Toepfer et al. (2021). Briefly, the Davis whorl damage scale ranges from "0" to "9", whereby a fully intact whorl is attributed a score of "0", while an almost totally destroyed whorl is attributed a score of "9". Minor damages are represented by scores ranging from 1-3, while moderate or severe damages by scores ranging from 4-6 or 7-9, respectively.

FAW infestation:Five days after the third application of the treatments, we evaluated FAW infestation levels. For this, ten plants were destroyed in each plot to search for caterpillars. The occurrence (yes/no) of young caterpillars (shorter than 0.5 cm) was determined as a proxy for re-infestation, whereas the number of older caterpillars (longer than 0.5 cm) was used as a proxy for treatment efficacy.

Number of cobs:At harvest, the number of fully-developed and underdeveloped cobs from 30 plants per plot was recorded.

Cob damage:Fully-devloped cobs were husked to visually evaluate cob damage, using a "0" to "3" customized damage score, where "0" represents an intact cob, while scores of "1", "2", or "3" represent minor (<5% damaged kernels), moderate (5-20% damaged kernels) or severe (>20% damaged kernels) cob damage, respectively.

Yield:The husked cobs from 30 plants were weighed together to estimate fresh weight (FW) yield per plot.