E. U. Okonkwo

Bio: E. U. Okonkwo is an academic researcher. The author has contributed to research in topics: Sitophilus & Callosobruchus maculatus. The author has an hindex of 1, co-authored 1 publications receiving 146 citations.

The efficacy of four seed powders and the essential oils as protectants of cowpea and maize grains against infestation by Callosobruchus maculatus (Fabricus) (Coleoptera: Bruchidae) and Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae) in Nigeria

Abstract: Seed powders and the essential oils of Dennettia tripetela Baker F., Piper guineense Schum and Thonn, Mondora myristica (Gaerth) Dunal and Xylopia aethiopica Dunal A. Rich were evaluated for their effectiveness in protecting cowpea and maize grains during storage. D. tripetela powder mixed with maize grains, at 1.5 g per 25 g was significantly more effective (P < 0.05) than P. guineense, M. myristica and X. aethiopica in achieving 100% mortality of adults of Sitophilus zeamais in 24 h, and was also as effective as pirimiphosmethyl (10 ppm) in achieving 100% mortality of adult weevil in 24 h, 3 months after treatment at a dose of 3g per 25 g. There was no F1 emergence except in grains treated with M. myristica, X. aethiopica and the untreated controls. Essential oils of D. tripetela and P. guineense achieved 100% mortality of adults of Callosobruchus maculatus and Sitophilus zeamais in 24 h. Except in cowpea treated with X. aethiopica cowpea and maize grains treated with seed oils suppressed the e...

Current Status of Plant Products as Botanical Pesticides in storage pest management

Abstract: The increasing concern over the level of pesticide residues in food has encouraged researchers to look for alternatives of synthetic pesticides. Their indiscriminate use has led to the development of resistant strains of pests as well as different environmental and human health problems. Recently, in different parts of the world, attention has been paid towards exploitation of higher plant products as novel chemotherapeutants in plant protection. Because of non phytotoxicity, systemicity, easy biodegradability and stimulatory nature of host metabolism, plant products possess the potential in pest management. Used widely until the 1940’s, these natural pesticides were displaced by modern synthetic pesticides that at the time seemed cheaper, easier and long lasting. The popularity of botanical pesticides is once again increasing and some plant products are being used globally as green pesticides. The body of scientific literature documenting bioactivity of plant derivatives to different pests continues to expand, yet only a handful of botanicals are currently used in agriculture. Pyrethroids and neem products are well established commercially as botanical pesticides and recently some essential oils of higher plants have also been used as antimicrobials against storage pests because of their relatively safe status and wide acceptance by the consumers. Some of the volatile oils, which often contain the principal aromatic and flavouring components of herbs and spices, have been recommended as plant based antimicrobials to retard microbial contamination and reduction in spoilage of food commodities. Furthermore, some of the antimicrobial plant products also possess strong antioxidant activities which are favourable properties to combat free radical mediated organoleptic deterioration of plant commodities and enhancing their shelf life. In the context of agricultural pest management, botanical pesticides are best suited for use in organic food production in industrialized countries but can play a much greater role in the production and post harvest protection of food products in developing countries.

Repellent Activity of Essential Oils and Some of Their Individual Constituents against Tribolium castaneum Herbst

Abstract: A tool for integrated pest management is the use of essential oils (EOs) and plant extracts. In this study, EOs from Tagetes lucida , Lepechinia betonicifolia , Lippia alba , Cananga odorata , and Rosmarinus officinalis , species grown in Colombia, were analyzed by gas chromatography-mass spectrometry. These oils as well as several of their constituents were tested for repellent activity against Tribolium castaneum , using the area preference method. The main components (>10%) found in EOs were methylchavicol, limonene/α-pinene, carvone/limonene, benzyl acetate/linalool/benzyl benzoate, and α-pinene, for T. lucida, L. betonicifolia, L. alba, C. odorata, and R. officinalis, respectively. All EOs were repellent, followed a dose-response relationship, and had bioactivity similar to or better than that of commercial compound IR3535. EOs from C. odorata and L. alba were the most active. Compounds from EOs, such benzyl benzoate, β-myrcene, and carvone, showed good repellent properties. In short, EOs from plants cultivated in Colombia are sources of repellents against T. castaneum.

Toxicity and repellency of origanum essential oil and its components against Tribolium castaneum (Coleoptera: Tenebrionidae) adults

Abstract: The components of Origanum vulgare L. essential oil showing insecticidal activity and repellency against red flour beetle, Tribolium castaneum (Coleoptera: Tenebrionidae), adults were analysed by GC-MS. All constituents were identified, and the main components were carvacrol (67.2%), p-cymene (16.2%), γ-terpinene (5.5%), thymol (4.9%), and linalool (2.1%). In a vapor phase fumigant assay, the origanum oil was more effective in closed conditions (LD50 = 0.055 mg/cm3) than in open conditions (LD50 > 0.353 mg/cm3). This suggests that toxicity is exerted largely in the vapor phase. Based on 24-h LD50 values, the toxicity of caryophyllene oxide (0.00018 mg/cm3) was comparable with that of dichlorvos (0.00007 mg/cm3). In addition, thymol, camphene, α-pinene, p-cymene, and γ-terpinene showed good insecticidal activity (LD50 = 0.012–0.195 mg/cm3). In repellency tests using 9 constituents of origanum oil, caryophyllene oxide showed complete repellency at 0.03 mg/cm2. Hydrogenated monoterpenoids, such as thymol, α-pinene, carvacrol, and myrcene, elicited strong repellency at 0.03 and 0.006 mg/cm2. Repellency depended on both time and concentration. These results indicate that origanum oil and its components could be potential candidates as a fumigant and repellent for managing T. castaneum adults.