Larvicidal effect of an N-isobutyl-(2E,4E,8Z,10E/Z)-dodecatetraenamides-rich extract of Salmea scandens on fall armyworm

Aim of study: To determine if secondary metabolites present in an ethanolic extract of Salmea scandens could be considered as a viable alternative for the control of fall armyworm (Spodoptera frugiperda larvae), as this is the most important maize pest in terms of economic losses to agriculture worldwide. Area of study: S. scandens shrubs were collected in San Rafael Toltepec, Oaxaca, Mexico. The laboratory assays were conducted at CIIDIR Oaxaca, and preliminary field assay was carried out in Zaachila Oaxaca. Material and methods: N-isobutyl-(2E,4E,8Z,10E/Z)-dodecatetraenamides-rich extract of S. scandens, corroborated by nuclear magnetic resonance (1H NMR and 13C NMR) and Fourier transform infrared (FTIR), was obtained from S. scandens by 10-day maceration in ethanol. The effect of the extract on the mortality of S. frugiperda larvae was investigated in the laboratory (in vitro) by topical application, and in the field (in situ), testing both topical and spraying applications. Main results: The 1H NMR, 13C NMR and FTIR spectra evidenced the obtention of the alkylamides-rich ethanol extract of S. scandens. Mortality of S. frugiperda in vitro increased with dose and monitoring time, reaching up to 80%. Under field conditions 63% of mortality was recorded at a dose of 0.30 mg µL-1 per larva by topical application, and 49% by spray application at a dose of 0.15 mg µL-1 per larva. Research highlights: The ethanolic extract of S. scandens can be considered a viable alternative for controlling fall armyworm S. frugiperda.