Egyptian Journal of Biological Pest Control, 25(1), 2015, 129-134 Insecticidal Effect of Essential Oils from Two Aromatic Plants Against Tribolium castaneum (Herbst), (Coleoptera: Tenebrionidae) Karima S. Khater * and Samah N. El-Shafiey ** * Zoology Department, Faculty of Science, Zagazig University, Zagazig, Sharkia, Egypt. ** Plant Protection Research Institute, Agricultural Research Center, Giza, Egypt. (Received: February 18, 2015 and Accepted: April 12, 2015) ABSTRACT Insecticidal activities of essential oils extracts from Wedelia trilobata (Fam.: Astracae) and Melissa officinalis (Fam.: Lamiacae) were assessed against the stored grain red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae). The effect of these oils on larval mortality, total protein, Asparate aminotransferase (AST), Alanine aminotransferase (ALT) and α amylase activity were investigated, using the last instar larvae. Chemical compositions of both oils were identified using GC/MS analysis. α-pinene, limonene, α phellandrene and β phellandrene were the major compounds identified inW. trilobata essential oil, while Eucalybtol, citronellol, caryophyllene oxide and carveol trans were the major ones identified in M. officinalis essential oil. Larval mortality of T. castaneum was recorded after 24h. The essential oil of W. trilobata (LC50 = 6.2%) was more effective than that of M. officinalis (LC50 = 16.4%). Treatment with median lethal concentrations of both oil extracts increased total protein content and decreased the AST, ALT and α amylase activity in larvae. Key words: Wedelia trilobata, Melissa officinalis, Aromatic plants, Essential oils, Tribolium castaneum, Protein- α amylase. INTRODUCTION The global post-harvest grain losses by insect damage and other bioagents ranges from 10 to 40%. The red flour beetle, Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) is one of the most widespread and destructive stored product pests throughout the world. Beetles and larvae feed on a very wide variety of dry vegetable substances, such as milled cereal products (Rees, 2004). Methods used to control stored grain insect pests included physical, chemical, and biological treatments (Isman, 2006). Chemicals largely used as pesticides in crop protection could have undesirable effects such as ozone depletion, environmental pollution, toxicity to non-target organisms, pest resistance, and pesticide residues, in addition to direct toxicity to users (Sousa et al., 2009). Therefore, the development of bioinsecticides has been focused as viable pest control strategy in recent years (Shaaya et al., 1997 and Isman, 2000). Plants may provide potential alternatives to currently used insect-control agents because they constitute a rich source of bioactive chemicals (Kim et. al., 2002). Aromatic plants are among the most effective insecticides from botanical origin and essential oils often constitute the bioactive fraction of plant extracts (Shaaya et al., 1997). Essential oils are secondary metabolites abundant in aromatic plant families such as Lamiaceae and Apiaceae which contain a large number of compounds e.g. monotrepens and sesquiterpens (Isman et al., 2007). Essential oils are known to exhibit low toxicity to mammals and have insecticidal effects (Islam, 2009). Bioactivity of essential oils is directly related to their chemical composition (Tawatsin et al., 2006). Essential oils possess acute contact and fumigant toxicity to insects (Sahaf et al., 2008 and Abdelgaleil et al., 2009), repellent activity (Nero et al., 2009), antifeedant activity (Huang et al., 1997) as well as development and growth factors (Waliwitiya et al., 2008). Wedelia trilobata, commonly called yellow dots (Asteraceae), is a dwarf shrub (about 60 cm in height). Previous studies revealed the insecticidal effects of W. trilobata extracts. Khater (2009) reported that fruits, leaves and stem extracts are used against Synthesomyia nudiseta larvae. Melissa officinalis known as lemon balm is a perennial herb in the mint family Lamiaceae, native to south-central Europe, North Africa, the Mediterranean region and Central Asia. M. officinalis has insecticidal and antimicrobial activities. Pavela (2005) reported toxic effect of M. officinalis and L. angustifolia essential oil against Spodoptera littoralis larvae. Objective of the present investigation was to evaluate the impacts of W. trilobata and M. officinalis essential oils on larval mortality, total protein content, AST, ALT and α amylase activity in last instar larvae of T. castaneum. MATERIALS AND METHODS Plant material and essential oil extraction Leaves and stems of M. officinalis and W. trilobata were crushed. Essential oils were extracted from the plant samples using a Clevenger –type apparatus (Marcus and Lichtenstein, 1979), where the plant material is subjected to hydrodistillation for 24 h. Anhydrous sodium sulphate was used to remove water after extraction. The extracted oils were stored in a refrigerator at 4ºC until use in the experiments.