Control of Callosobruchus maculatus (FABR.) (Coleoptera: Chrysomelidae: Bruchinae) in Vigna unguiculata (L.) WALP. with essential oils from four Citrus spp. plants

The cowpea weevil, Callosobruchus maculatus (F.), is a major pest of cowpea Vigna unguiculata (L.) Walp. in storage units, making the grains unsuitable for consumption. The adverse effects of chemical control methods have been motivating the demand for alternatives in pest control, such as the use of natural products like essential oils. The aim of this study was to obtain and chemically identify the components of essential oils extracted from fruit peels of Citrus latifolia Tanaka, Citrus reticulata Blanco, Citrus sinensis L Osbeck and Citrus paradisi Macf., as well as to determine the contact and fumigant toxicity of these oils and their repellent effect on C. maculatus adults. The GC-MS analysis identified 45 compounds in the essential oils; the major components were described as follows: C. latifolia (limonene 57.7%, gamma-terpinene 17.2%, beta-pinene 12.3%, alpha-pinene 2.0%), and C. sinensis (limonene 93.8%, myrcene 2.1%), C. reticulata (limonene 94.2%, myrcene 1.6%) and C. paradisi (limonene 94.2%, myrcene 1.8%). In the contact toxicity tests using treated cowpeas the LC50 values ranged from 943.9 to 1037.7 ppm, with the lowest value for C. latifolia and the highest for C. sinensis. The number of eggs and newly emerged adults was inversely proportional to essential oil concentration increase. In the fumigant toxicity test, LC50 values ranged from 10.2 to 12.98 mu L/L air, with C. latifolia showing the best results. In the repellency test, the essential oils were classified as neutral at all concentrations. The percentages of oviposition reduction ranged from 29.74 to 71.66%, while reduction in emergence varied from 15.43 to 85.31%. Essential oils of citrus peels (industrial waste) could be widely used for C. maculatus control. Moreover, they could gain economic value if used on a large scale to produce essential oils. (C) 2016 Elsevier Ltd. All rights reserved.