Lethal and sublethal effects of chemical constituents from essential oils on Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae: Bruchinae) in cowpea stored grains

The recent use of essential oils has been considered an important approach in pest management programs for stored products. Regarding essential oils, it is of great importance to understand the role of each chemical constituent in the toxic activity on insects. These chemical constituents may exhibit potential for postharvest disinfestations of stored grains, causing lethal (mortality) and sublethal effects, such as oviposition deterrence or repellency. For that, this study aimed to evaluate the bioactivity of five chemical constituents from essential oils on the mortality, oviposition, emergence of adults, population growth and repellency of Callosobruchus maculatus (Fabr., 1775) on cowpea Vigna unguiculata (L.) Walp stored grains. The terpenes limonene, geraniol and α-pinene, as well as the phenylpropenes eugenol and trans-anethole, were used. The LC50 and LC95 of the chemical constituents ranged from 60.99 to 2142 ppm and 79.76 to 3217 ppm, respectively. The number of eggs and emergence of adults were inversely proportional to the increase in concentrations. The instantaneous rate of growth (ri) was negative at the highest concentrations used. The chemical constituents α-pinene and geraniol were repellents at levels of LC50 and LC95. The results of this work demonstrated that the compounds isolated from essential oils used are effective in the control of C. maculatus, because they presented high contact toxicity and reduced population growth (trans-anethole), reduced oviposition and insect emergence (geraniol and eugenol) and were repellent (geraniol and α-pinene).