Essential oils from Betula lenta, Cinnamomum cassia, Citrus aurantium var. Amara and Acorus calamus as biopesticides against cowpea weevil

Abstract

Cowpea (Vigna unguiculata) is an important crop as a source of basic protein for populations in tropical countries, generating profit after the processing and storage of grains. However, the attack of pests such as cowpea weevil Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae) can limit the production of cowpea, with the insect causing qualitative and quantitative losses to the grains. Its control is commonly performed with fumigant phosphine, which due to its almost exclusive use, has selected resistant populations of insects, causing control failure. This way, the present research aimed to investigate the effects of essential oils of Betula lenta, Cinnamomum cassia, Citrus aurantium var. Amara and Acorus calamus in the treatment of cowpea grains [Vigna unguiculata (L.) Walp.] under storage conditions, for the management of Callosobruchus maculatus. The effects of essential oils were investigated through contact, fumigation, and repellency tests. The LC50 found in the test of contact was 0.61; 0.63; 0.64 and 22.98 μL/20 g of beans for the oils of A. calamus, B. lenta, C. cassia, and C. auratium var. Amara, respectively. Based on the data, the number of eggs and insects that emerged decreased as the concentration of essential oils increased. The LC50 values in the fumigation test were estimated at 5.16; 8.24; 25.84 and 35.31 μL/L of air for A oils. calamus, B. lenta, C. auratium var. Amara and C. cassia, respectively. In the repellency test, all oils acted like antagonists to C. maculatus biology, but the latter presented deterrence against the oviposition and the emergence of adults in most concentrations. These findings indicate that essential oils can be used to manage C. maculatus.