Oils extracted from Cymbopogon citratus, Lantana camara, Artemisia camphorata, and Imperata cylindrica plants were used as potential insecticides against the rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae). The phytochemical composition of the isolated oils was identified by gas chromatograph-mass spectrometry (GC-MS). Oil contact toxicities were evaluated against the adults of S. oryzae. The activities of acetylcholinesterase (AChE), alkaline phosphatase (ALP), and transaminases enzymes (AST) were measured. L. camara oil (LC50 = 9.81 mg/cm2) demonstrated the highest effect, followed by C. citratus oil (LC50 = 10.89 mg/cm2), A. camphorata EO (LC50 = 16.12 mg/cm2), and I. cylindrica oil (LC50= 36.85 mg/cm2) against the adults of S. oryzae. The inhibition percentages of AChE were 38.8, 41.7, 35.0, and 27.2%; ALP were 42.4, 49.3, 28.1, and 18.7%; AST were 33.9, 38.7, 20.8, and 11.8%; and ALT were 22.7, 30.5, 14.6, and 9.6% after treated S. oryzae with oils from C. citratus, L. camara, A. camphorata and I. cylindrica, respectively. The highest abundant compounds in C. citratus were geranial (25.95%), nerylacetal (8.85%), and neral (8.45%), in L. camara were caryophyllene (12.2%), and 3-elemene (8.89%), in A. camphorata were germacrene D-4-ol (20.83%), and borneol (19.47%), and in I. cylindrica were 5-phenylundecane (10.68%), and 6-phenyldodecane (8.70%).

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The effect of six plant essential oils against three stored grain insects, Sitophilus oryzae, Rhizopertha dominica and Tribolium castaneum were studied under laboratory conditions. The tested oils are namely, fennel oil (Foeniculum vulgare), caraway oil (Carum carvi), cinnamon oil (Cinnamomum verum), citronella oil (Cymbopogon winterianus), nutmeg oil (Myristica fragrans) and black cumin oil (Nigella sativa). The result showed that increasing of the oil concentration and exposure times significantly increased the mortality percentage.Generally, the toxicity of essential oils at all tested concentrations increased with the increasing of exposure time. So, the results indicated that toxicity of all tested essential oil against the three stored grain insects at the high concentration was recorded high mortality faster than low concentration.The tested essential oils significantly decreased the different haemocyte counts in tested insects, cinnamon oil markedly increased the haemocyte surface areas in the tested insects especially the surface area of oenocytoides in T. castaneum.The recorded results indicate that the essential oils of fennel, caraway, cinnamon and citronella could be applicable to the management of S. oryzae, R. dominica and T. castaneum adults.

Induced plant resistance is an important component of pest control. Therefore, effects of potassium silicate (K2SiO3) on the survival, development and reproduction of Aphis gossypii Glover at various life stages were tested under laboratory conditions. Efficacy of foliar spraying with K2SiO3 compared to lambda-cyhalothrin (LCH) against the field strain of A. gossypii third nymphal instar under greenhouse conditions as well as its impacts on the activity of antioxidant enzymes were also evaluated. In laboratory studies, K2SiO3 (LC50 = 58.21 mg L -1 ) was less toxic than LCH (LC50 = 44.32 mg L -1 ) against A. gossypii first nymphal instar after 48 h treatment. There was no significant difference in the developmental duration of total nymphal stages among the three treatment concentrations (LC10, LC25 and LC50) and the control. Treatments with K2SiO3 significantly reduced the longevity and fecundity of adult aphids. Reduction percentages of A. gossypii field strain after feeding on cotton leaves sprayed with K2SiO3 were 47.1 and 55.0 % at 100 and 200 mg L -1 , respectively, compared to 67.9 and 77.5% in LCH. The higher levels of catalase and polyphenol oxidase enzymes activities was observed at 24 h with percentages 68.16 and 32.74%, respectively, compared to the control, then declined and reached to minimum value at 96 h. However, peroxidase enzyme activity was increased with percentage 59.72 % at 12 h and decreased to reach minimum value at 48 h. This study could introduce promising plant resistance inductors for use in integrated pest management of A. gossypii on cotton plant.

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