Antioxidant activities of essential oils of Clausena anisata (Rutaceae) and Plectranthus glandulosus (Labiateae), plants used against stored grain insects in North Cameroon

This study was carried out to evaluate the overall antioxidant capacity of the essential oils of the leaves of Clausena anisata (Rutaceae) and Plectranthus glandulosus (Labiateae), commonly used in the traditionalmethod of grain storage in the northern part of Cameroon. Towards this objective, the co-oxidation of β-carotene as well as the reducing power, the radical scavenging capacity and the conjugated dienes profile of theessential oils during storage for a period of 10 days at 28 ± 2.2 °C and 65±5.7% RH were determined. The least concentration necessary to prevent 50% oxidation (EC50) of β-carotene was found to be 6.53 mg/l, 5.84 mg/l and 524 μg/l respectively for C. anisata, P. glandulosus and butylated hydroxytoluene (BHT) which was the control. On the other hand, the reducing power of the different oils in a decreasing order was found to be P. glandulosus (EC50=2.41) > C. anisata (EC50=1.77 mg/l) while the EC50 of Scavenging abilities were 2.66 and 3.02 mg/l for C. anisata and P. glandulosus respectively. Based on the conjugated dienes profile, the essential oils showed higher antioxidant activity compared to Butylated hydroxytoluene (BHT) activity. The effective time (ET50) of the formulation ranging from 300 to 1000 ppm varied from 2 to 8 days for C. anisata and from 3 to 11 days for P. glandulosus. For the control (BHT), the effect varied from 5 to 15 days at an exposition temperature of 50 °C.Key words: Antioxidant activity; Clausena anisata; Plectranthus glandulosus; Stored products; Scavenging ability; Reducing powe

Tribolium castaneum (Coleoptera: Curculionidae) sensitivity to repetitive applications of lethal doses of imidacloprid and extracts of Clausena anisata (Rutaceae) and Plectranthus glandulosus (Lamiaceae)

Nowadays, chemical control strategies in crop protection are mostly based on biopesticides or on low persistence synthetic molecules. These tools are alternatives of some products exhibiting adverse effects on consumers and polluting environment. Biopesticides made of essential oils of aromatic plants are more and more advised as user and environmental friendly crop protectants. Few works reviewed consequences of their repetitive use on the capability of the pest to resist to their insecticidal efficiency. The present work was carried out to compare the variation in the efficiency of a synthetic insecticide, imidacloprid and essential oils of Clausena anisata (Rutaceae) and Plectranthus glandulosus (Lamiaceae) against the flour beetle Tribolium castaneum (Coleoptera: Tenebrionidae), during 4 generations (F4). The lethal dose of these insecticides that causes 80% of mortality (LD80) at the first generation killed at the 3rd generation, 60% of pest for the two essential oils and 25% for imidacloprid. At the 4th generation, 25% of the pest populations were killed by the essential oils and 5% by imidacloprid applications. Egg and post-ovum development time differed among generations (P < 0.001). However, the fecundity of sensitive females was greater than that of resistant ones treated with essential oils. Insects treated with imidacloprid exhibited important fecundity in advanced generations. The LD50 level of the F4 treated with imidacloprid is 10 times that of the parental generation; however, the increase doubled from the parent to the F4 while treated with the essential oils. This work showed that T. castaneum could acquire resistance to imidacloprid faster than to 2 tested essential oils. © 2010 International Formulae Group. All rights reserved.Keywords: Chemical control, Essential oils, Imidacloprid, Susceptibility, Stored products, Tribolium castaneum

Effectiveness of binary combinations of Plectranthus glandulosus leaf powder and Hymenocardia acida wood ash against Sitophilus zeamais (Coleoptera: Curculionidae)

Abstract Background Botanicals are generally assumed to be more biodegradable, leading to less environmental problems. Combination of botanicals could enhance biological activity against insect pests. Hence, the amount of botanical used for the control of stored grain pests may be minimised. In this study, the bioassay was carried out on Sitophilus zeamais to assess the effectiveness of binary combinations of Hymenocardia acida wood ash and Plectranthus glandulosus leaf powder. The quantities of mixed products were added to maize grains to constitute the contents of 5, 10, 20 and 40 g/kg. Then, the bioassays on toxicity within 1, 3, 7 and 14 days exposure, progeny production, population increase, grain damage and germination ability of protected grains were carried out. Results The major compounds (pinene, α-pinene, α-terpineol, thymol, β-myrcene and 3-carene) of P. glandulosus leaf powder were monoterpenes. The major non-monoterpenic constituent was an oxygenated sesquiterpene, β caryophyllene oxide. The chemical analysis of H. acida ash showed that calcium (5800 mg/kg) and phosphorus (2782 mg/kg) recorded higher content than the other minerals. Plectranthus glandulosus leaf powder, H. acida wood ash and their binary combinations significantly induced mortality of S. zeamais adult (P < 0.0001). The higher mortality rate was achieved by the highest content within 14 days of exposure. The combinations of P. glandulosus leaf powder with H. acida at different proportions produced different interactions. The mixture of 75% P. glandulosus and 25% H. acida produced synergistic effect, whereas the mixture of 50:50 had antagonistic effect in weevil mortality. The three combinations of H. acida and P. glandulosus significantly reduced the production of the progeny compared to the control. From the application of 5 g/kg (lowest content), the number of emerging adults was highly reduced. The combination 25PG75HA revealed to be more effective than the two other against F1 production. The grain damage and population growth were significantly reduced. In general, the non-infested maize grain had a good germination rate than the infested ones. The treatment did not have negative effect on seed germination. Conclusions From our results, the two powders and their binary combinations could be used to reduce grain infestation by insect while taking into account the proportions of insecticidal powders implied in the combination

The use of plant extracts for stored product protection

A wide range of plant extracts have been used alternatively to chemical insecticides against stored product insect pest species. These substances could be used alone or in combination with other alternatives or synthetic insecticides in order to enhance their action. Botanicals can be applied with the same techniques that are used for the application of traditional contact insecticides or fumigants. Given that stored product insects exhibit different levels of sensitivity or tolerance to plant extracts, a wide screening of these substances has been carried out to widen the available tools against these harmful organisms with interesting results. © 2014 Springer India. All rights reserved