Insecticidal activity of three essential oils against two new important soybean pests: Sternechus pinguis (Fabricius) and Rhyssomatus subtilis

In the present study, the essential oils from Eucalyptus globulus Labill., Citrus sinensis L. Osbeck and Citrus limon L. were analysed by GC-MS (gas chromatography–mass spectrometry) and evaluated for their toxic effects on Sternechus subsignatus and Rhyssomatus subtilis, two important pest of soybean in South America. Contact toxicity assayed by impregnation on filter paper discs showed that these oils caused significant mortality of the test insects (100% of mortality at 5 µL/cm 2 ). Eucalyptus oil (98.9 % of 1,8-cineole) had the greatest contact toxicity (LD50 = 0.40 and 0.84 µL/cm 2 for S. pinguis and R. subtilis, respectively), whereas orange (87.6 % of limonene) and lemon oils (62.5 and 12.6 % of limonenen and β pinene, respectively) were less toxic (LD50 > 1 µL/cm 2 for both insects). All the responses were found dose-dependent. Rhyssomatus subtilis was more resistant than Sternechus pinguis to the toxicity of the essential oils studied.