Protection of cowpea seeds and toxicity against cowpea weevils by the essential oils from Lippia alba (verbenaceae) and Schinus terebinthifolius (anacardiaceae)

Abstract

Alternative methods have been widely studied to mitigate problems arising from the use of pesticides in agriculture. Among them is the use of essential oils to control stored grain pests. In this context, the aim of this study was to evaluate the effect of fumigation of cowpeas with 12 essential oils having different chemical profiles, derived from the germplasm collection of Schinus terebinthifolius and Lippia alba at Rio de Janeiro Federal Rural University. These oils were applied at various concentrations (0.1–1.0 mg/mL of air) against cowpea weevils (Callosobruchus maculatus). The chemotypes evaluated included citral, citral/limonene, carvone/limonene, and linalool from the essential oils of L. alba, as well as α-pinene, sabinene, α-phellandrene/α-pinene, β-pinene/α-pinene, δ-carene/α-pinene, limonene, α-phellandrene/sabinene, and myrcene from the essential oils of S. terebinthifolius. Various aspects of the insects' reproductive cycle were evaluated, including mortality, egg laying, emergence of new adults, emergence rate, and larval hatching, along with grain mass loss. The results indicated life cycle inhibition of all evaluated oils, with the essential oil from the UFRRJ ECB028 (linalool CT) genotype having the lowest LC50 (0.10 mg/mL of air), completely halting the insects’ life cycle and totally preventing seed mass loss. Overall, the results pointed to certain genotypes as promising for the development of technologies aimed at seed protection.