Insecticidal effects of essential oils from two Eucalyptus species and pathogenic fungi, Lecanicillium muscarium, against cotton aphid, Aphis gossypii Glover
The search for environmentally friendly insecticidal substances is necessary because of the negative effects of conventional chemical insecticides. In the present study, the insecticidal activities of the essential oils of Eucalyptus microtheca and E. spathulata and the entomopathogenic fungus, Lecanicillium muscarium (Zare & Grams), were assessed against cotton aphid, Aphis gossypii Glov. (Aphididae). The essential oils extracted by Clevenger apparatus and their chemical analysis made by gas chromatography-mass spectrometry (GC-MS). 1,8-cineole (33.77%) and α-pinene (11.14%) in the E. microtheca and 1,8-cineole (42.63%) and ectan (19.90%) in the E. spathulata essential oils were found as main components. A. gossypii was very susceptible to the tested essential oils and the LC50 values were 12.366 and 15.952 μl/l for E. spathulata and E. microtheca essential oils, respectively. The 1 day-LC50 value with L. muscarium was 5.203×109 spore/ml. By increasing the time, the LC50 value was decreased and reached to 8.583×102 spore/ml after 5 days. A synergistic effect between the sub-lethal concentrations of essential oils with L. muscarium has been achieved but by increasing of concentrations, this effects has changed to antagonistic one. According to the results of the present study, the essential oils of E. microtheca and E. spathulata and L. muscarium fungus can be introduced as safe alternatives to the chemical insecticides in the management of A. gossypii.