Contact and fumigant toxicity and repellency of Eucalyptus citriodora Hook., Eucalyptus staigeriana F., Cymbopogon winterianus Jowitt and Foeniculum vulgare Mill. essential oils in the management of Callosobruchus maculatus (FABR.) (Coleoptera: Chrysomelidae, Bruchinae)

Abstract

The weevil Callosobruchus maculatus (Fabr.) is considered the most important pest of cowpea, Vigna unguiculata (L.) Walp., stored in tropical and subtropical countries. Secondary compounds extracted from plants can be used in its control, as a potential alternative to synthetic insecticides. Therefore, the present study aimed to: (a) make the chromatographic and mass spectrometry analyses of the essential oils of Eucalyptus citriodora Hook, Eucalyptus staigeriana F., Cymbopogon winterianus Jowitt and Foeniculum vulgare Mill; (b) to evaluate the contact and fumigant toxicity; (c) test the repellent effect. The oils' main compounds were: E. citriodora (citronellal 89.59%; citronellyl acetate 3.34%; 1,8-cineole 2.87%), E. staigeriana (limonene 28.75%; geranial 15.20%; neral 12.16%), C. winterianus (geranial 21.83%; citronellal 10.94%) and F. vulgare (limonene 41.82%; (E)-anethole 17.91%; α-pinene 11.13%). The LC50s of F. vulgare, E. citriodora, C. winterianus and E. staigeriana in contact tests were estimated at 178.13, 298.17, 328.42 and 345.57 ppm cowpea grains, respectively. According to regression analyses, the higher the oil concentration, the lower the number of laid eggs and emerged insects. In fumigation tests with adults, LC50s ranged from 2.58 to 7.85 μL/L of air, while the toxicity ratios ranged from 1.25 to 3.04. In all concentrations tested, the E. citriodora and C. winterianus oils were repellent to adult C. maculatus; F. vulgare was classified as neutral, while E. staigeriana was neutral at lower than 558 ppm concentrations and repellent at higher concentrations. Regarding the essential oils tested, the percentage of oviposition reduction varied from 6.3 to 100%, while emergence percentages varied from 0.9 to 100%.