Chemical Composition and Use of Momordica charantia L. and Hyptis spicigera Lam. Extracts as Mosquito Larvicides and Insect Growth Regulators against Malarial Vector, Anopheles gambiae Giles

Background: Mosquitoes are responsible of numerous vector-borne diseases and among these diseases is malaria which takes away lives of thousands of people, especially children of under five, particularly in Africa. To reduce the mortality and economic burdens of this deadly disease, synthetic insecticide has been of use to control its main vector, Anopheles gambiae. Due to adverse effects caused by these conventional products on non-target organisms and the environment, plants have been of first choice as they proved their effectiveness against mosquitoes and are said to be eco-friendly and relatively safer. Therefore, the aim of this study was to screen the phytochemicals and determine the larvicidal and adult emergence exhibitory activities of Momordica charantia and Hyptis spicigera leaves extracts against Anopheles gambiae larvae. Methods: The WHO standard protocol for larvicidal activity and IGRs was followed up and concentrations from 500 - 2000 ppm for larvicidal and 500 - 1500 ppm for IGRs were set up. Results: There was the presence of alkaloids, flavonoids, tannins, phenols, steroids, terpenoids and oils in Momordica charantia against alkaloids, taponins, tannins, phenols, steroids, terpenoids and oils in Hyptis spicigera. Methanol crude extract registered the lowest LC50 value of 270.6 ppm followed by ethyl acetate and hexane fractions recorded the LC50 of 742.1 and 756 ppm, respectively for larvicidal activity of Momordica charantia against LC50 of 760 and 867.5 ppm for hexane fraction and methanol crude extract, respectively for Hyptis spicigera. Methanol crude extract and hexane fraction of both plants as well as the ethyl acetate fraction of M. charantia registered greater emergence inhibition with IE50 values of 590.2, 842.3 and 982 ppm for methanol crude extract, hexane and ethyl acetate fractions of M. charantia, respectively against 901.7 and 873.2 for methanol crude extract and hexane fraction of H. spicigera, respectively. Conclusion: The toxicity and adult emergence inhibition may be associated with constituents in both plants that interfere with the normal neuronal, respiratory and endocrine systems functions.

Chemical Composition, Larvicidal and Adult Emergence Inhibition Activities of Balanites aegyptiaca Del. Seed and Aristolochia albida Duch. Root Extracts against Malaria Vector, Anopheles gambiae Giles

Background: Anopheles gambiae is enemy number one of mankind in Africa and particularly in Cameroon due to its ability of transmitting malaria which is the deadliest disease in this part of the world. Synthetic insecticides have been used to control malaria vectors but they have negative effects on non-target organisms and are environmentally unfriendly. Control of mosquitoes at larval stages using phytochemicals is currently the leading tool to reduce the mosquito population and so the reduction of malaria transmission rates. Therefore, the present study was to evaluate the phytochemical contents, larvicidal and adult emergence inhibition activities of Balanites aegyptiaca seed and Aristolochia albida root solvents extracts against Anopheles gambiae larvae. Methods: The World Health Organization standard protocols were followed for the different bioassays. Concentrations ranging from 500 - 2000 ppm for larvicidal and 500 - 1500 ppm for IGRs were used. Results: Both plants showed the presence of alkaloids, flavonoids, saponins, tannins, phenols, terpenoids and oils except the absence of phenols in Aristolochia albida. The larvicidal activity of Aristolochia albida extracts showed that hexane and methanol fractions were the most active killing relatively all exposed larvae with the LC50 values of 420.1 and 453 ppm, respectively. The same observation was made in hexane fraction from Balanites aegyptiaca (LC50 = 588 ppm). The insect growth inhibitory activity of Aristolochia albida extracts proved that hexane and methanol fractions relatively caused a 100% inhibition in the mosquito development, recording the EI50 values of 482.4 and 555.6 ppm, respectively. The same trend was observed with Balanites aegyptiaca hexane fraction registering better EI50 of 623.9 ppm. Conclusions: Our findings demonstrate that Balanites aegyptiaca seed and Aristolochia albida seed extracts are rich in phytochemicals capable of killing mosquito larvae and disrupting mosquito larval development. This could contribute to the control of mosquito populations and improved management of malaria.

Plants Extracts and a Mycoinsecticide in Cowpea Yield Improvement in Guinean Savanah and Sahelian Savanah Agro-Ecological Zones of Cameroun

Cowpea yield improvement is done by adding agricultural inputs. The use of natural substances as pesticides is being encouraged to fight against cowpea field pests. The pesticidal potentials of Azadirachta indica and Boswellia dalzielii water extracts, Metarhizium anisopliae, alone and in combination with plant extracts, and a commercial synthetic pesticide (Decis®) were tested in field on two varieties of cowpeas, Vigna unguiculata in two agroecological zones (Guinean Savanah and Sahelian Savanah) of Cameroon. The field trials were carried out in a full randomized block design including nine treatments and a control. Four replications were made concerning the different treatments and control. At the flowering stage, the cowpea field was sprayed three times with different pesticidal formulations at the interval of five days. The number of ramifications per plant, and that of pods per block and seed yield were determined. The pesticide formulations considerably (p ®). Bafia variety treated with the combination of M. anisopliae and A. indica recorded the highest ramification rate (37.03 ± 1.59) in Maroua (Sahelian Savanah). The same variety also produced more important pods number (90.50 ± 16.66) in Ngaoundere (Guinean Savanah) with the binary combination of two plants used in this experiment. The highest seed yield (44.23 ± 2.31) was recorded in Ngaoundere with B125 variety treated with the combination of the three pesticidal formulations separately (A. indica, B. dalzielii, M. anisopliae). The plant products used in this work, M. anisopliae and their mixtures could supersede the synthetic pesticides considering environmental issue in cowpea crop protection. Then, such formulations would not only improve crop productivity but also preserve environment from the pollution due to the use of synthetic residual chemicals.

樟脑罗勒生物活性提取物对储藏豇豆和大豆中四纹豆象的影响（英文）

【目的】本研究旨在评价樟脑罗勒Ocimum canum Sims(唇形科)叶的正己烷、丙酮和甲醇提取物对四纹豆象Callosobruchus maculatus(F.)的杀虫、保护和驱避潜力。【方法】用剂量为1和5 g/kg豆粒的樟脑罗勒提取物包被处理豇豆和大豆豆粒,并以相同剂量的市售苦楝籽油进行包被处理作为参照。7 d内每隔1 d检查处理豆粒中四纹豆象成虫的死亡率。在四纹豆象的各个未成熟期,通过处理新产卵和幼虫,进行杀卵毒性和杀幼虫毒性测试。贮存4个月后评价豆粒受损情况和重量损失。应用线型嗅觉仪,通过选择试验测定驱避效果。【结果】提取物对四纹豆象成虫的毒性与市售苦楝籽油相同,在处理的豇豆中,提取物比市售的苦楝籽油毒性更强。5 g/kg豆粒提取物这一剂量处理7 d内,正己烷、丙酮和甲醇提取物分别引起54.2%±3.9%,62.9%±4.8%和60.3%±4.5%的成虫死亡。此外,与测试的标准杀虫剂相比,提取物激发这两种豆粒产生更强的驱避效果。这一产物对卵的毒性最强,对1和2龄幼虫的毒性比对其他发育阶段豆象的毒性强。正己烷提取物对2龄幼虫的毒性最强(致死率为81.0%±5.3%),而丙酮提取物和甲醇提取物对1龄幼虫的毒性最强,致死率分别为92.5%±7.5%和62.0%±15.7%。丙酮提取物对1和2龄幼虫的毒性与测试的标准杀虫剂相似,对蛹的毒性强于测试的标准杀虫剂。贮存4个月后,豇豆受损和重量损失分别减轻3倍和2倍多。【结论】本研究结果表明,樟脑罗勒提取物对四纹豆象具有潜在的驱避和杀虫活性,由于容易获得,因此强烈建议将该植物用于喀麦隆的害虫治理策略中。

Bioefficacy of Plectranthus kirbii Powder and Extracts on Stored Cowpea Pest Callosobruchus maculatus (Coleoptera: Chrysomelidae)

Cowpea seed constitutes an important source of proteins for populations in Sub-Saharan Africa. But this food resource is heavily damaged by cowpea beetle Callosobruchus maculatus. The control of that pest is mainly carried out by using synthetic insecticides. Despite the efficacy of this method, it caused environmental and health problems. Therefore, the search for alternative methods is vivaciously needed. In this issue, the bio-efficacy of Plectranthus kirbii extracts was assessed on C. maculatus regarding adult mortality, suppression of population and grain damage as well as seed viability preservation and repellency. The leaf powder and aqueous extracts of the plant were tested at 2, 4, 8 and 16 g/kg on bruchid adult for toxicity and damage bioassays. Repellency test was carried out using the plant aqueous, methanolic and ethyl acetate extracts at 0.5, 1, 2 and 4 mg/cm2. The seed viability was evaluated using seeds preserved for three months at the single concentration of 16 g/kg of each plant extract. Significant mortality of cowpea beetle was induced by the plant aqueous extract and leaf powder. LC50 values decreased with the increasing exposure period, and aqueous extract and leaf powder recorded 33.42 and 9.48 g/kg respectively within 3 days whereas within 5 days, the same extracts in the same order recorded LC50 of 1.31 and 8.73 g/kg respectively. These extracts significantly reduced damage by suppressing almost completely the bruchid population growth. The non-infested grain preserved recorded high grain viability compared to the infested ones. The non-treated infested recorded the lowest germination rate (11.33%). The repellency rate ranged from 38.75% to 83.75%. Ethyl acetate and methanolic extracts were classified as the class III repellent product, while aqueous extract ranged as class IV in repellency. Considering these findings, the extracts of P. kirbii could favourably replace the synthetic insecticides used in the cowpea protection during storage.