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Essential oils from three species of plants comprising three plant families were obtained by Clevenger-type water distillation. The major compounds in these essential oils were identified with GC-MS and their insecticidal activity against adult cotton aphid,Aphis gossypiiGlover tested with dosage-mortality bioassays. We examined mortality only for viviparous adults because sizeable aphid populations on cucumber (Cucurbitaceae) hosts are largely produced by these wingless, parthenogenic females. Three of the oils were directly applied to aphid females in randomised blocks at 25 ± 2 °C and 60 ± 5% R.H. and under a L16:D8 photoperiod. Essential oils were mixed with a non-toxic emulsifying agent, Tween 80. Results show adverse contact effects of essential oils studied in the control of cotton aphid. Probit analysis and LC50at concentrations at different exposures showed aphids were incapacitated and killed by aliphatic aldehydes, phenols and monocyclic terpenes contained inAzadirachta indica, Eucalyptus camaldulensisandLaurus nobilis. LC50on cotton aphid, for azadirachtin eucalyptus and laurel essential oils were respectively 5389, 9515 and 13730 ppm. In the current study, efficacy in respect to the contact toxicity (LC50) followed the order:A. indica > E. camaldulensis > L. nobilisafter 24 h treatment. Our results show quantitative and qualitative differences in the chemical composition and insecticidal activities of our essential oils. All oils became insect toxic as concentration increased. According to the results, essential oils of all the three plants have the potential to be employed in the pest management programmes that can be used in protection of greenhouse conditions against cotton aphid. [ABSTRACT FROM PUBLISHER]

The cotton aphid,Aphis gossypiiGlover (Hem: Aphididae), is one of the most injurious pests of fruits, vegetables and ornamental plants worldwide, both outdoor and indoor. Currently, the main method of control of this pest is through application of pesticides which is mostly accompanied by the resistance of the pest against pesticide(s). The resurgence of resistant aphid populations brings about further contamination of foodstuff and environment. Essential oils obtained from the aerial parts of plants may have the potential to be an alternative to synthetic pesticides, since they have been demonstrated to possess a wide range of bioactivities against insects and mites. So, the aim of the current study was to investigate the effect of essential oils extracted from three different plants namely:Azadirachta indicaAdr. Juss. (Meliaceae),Eucalyptus camaldulensisDehn. (Myrtaceae) andLaurus nobilisL. (Lauraceae) againstA. gossypii. The LC50values of essential oils ofA. indica,E. camaldulensisandL. nobilisagainstA. gossypiiwere 1.96, 2.28 and 3.16 μl L−1air, respectively. This shows thatA. indicapossesses the highest lethal activity whereasL. nobilisthe lowest. These data suggest that essential oils of all the three plants have the potential to be employed in the pest management programmes designed for a control ofA. gossypiiunder greenhouse conditions. [ABSTRACT FROM PUBLISHER]