Biologie

The aim of this study was to determine the insecticidal efficacy of mixture of NeemAzal a commercial neem product and Plectranthus glandulosus leaf powder against Callosubruchus maculatus and Sitophilus zeamais. Mixed at various proportions (100 + 0, 75 + 25, 50 + 50, 25 + 75 and 0 +100%, these powders were tested on adult mortality, inhibition of offspring production and their persistence on C. maculatus and S. zeamais. All the mixed NeemAzal and P. glandulosus caused significant mortality to adult C. maculatus and S. zeamais. No significant difference was observed among the mixed powders that were subjected to the three mixture proportions regarding the mortality they caused to the weevils. The mixed 75% NeemAzal + 25% P .glandulosus of powder led to a higher mortality (100%) of both insect species, three (5 g/kg) days post exposure. The three days LC50 values decreased with ascending proportion of NeemAzal in the mixture from 3.21 g/kg (25% NeemAzal + 75% P. glandulosus) to 0.24 ...

Botanical insecticides are among the most promising alternatives to synthetic insecticides for stored product protection. Calneem oil from Ghana and local neem oils from two localities in northern Cameroon (Garoua and Maroua) were tested at 0 (untreated control), 2, 4, 6, 8 and 12 ml/kg, on the adult and immature stages of the maize weevil Sitophilus zeamais (Motschulsky), for mortality and reproduction inhibition. The neem oils from Cameroon were extracted using the traditional kneading method and a hydraulic press in the laboratory (refined). Maize grains were coated with the five neem seed oils (Calneem, Garoua traditional and refined, and Maroua traditional and refined, respectively) and adult mortality was recorded at 1, 3, 7 and 14 days after exposure. Within 1 day of exposure, the highest tested concentration (12 ml/kg) of Calneem, Garoua traditional, Garoua refined, Maroua traditional and Maroua refined oils caused similar weevil mortality of 86.3, 93.8, 93.8, 97.5 and 97.5%, respectively. The 24-h LC 50 values for the oils in the same order were 7.0, 6.0, 5.0, 5.0 and 4.8 ml/kg, respectively. The lowest (2 ml/kg) and highest (12 ml/kg) concentrations of the oils suppressed progeny production by over 80 and 98%, respectively. The oils arrested the development of the hidden eggs and immature stages in the maize grains. The results suggested that neem seed oils from different localities of northern Cameroon, irrespective of the method of extraction, were effective for the protection of stored maize against S. zeamais. The promotion of natural neem seed oils as stored grain protectants in Cameroon would boost food security, alleviate poverty and reduce environmental degradation.

Azadirachta indica seed oil has long been used in many parts of the world for the control of various insect pests. The quantification of its known insecticidal compound Azadirachtin A on treated commodities remains a challenge. The degradation of Azadirachtin A in treated cowpea and maize was determined with HPLC-MS as well as the toxicity of A. indica seed oil on their respective major pests is storage between 0 and 180 days. Azadirachtin A degraded slowly on treated maize from 1.31 mg/kg (0-day) to 0.38 mg/kg (180-day) while on cowpea it degraded from 1.14 mg/kg (0-day) to 0.43 mg/kg (180-day). A. indica oil caused a significant day-dependent mortality of adults Callosobruchus maculatus and Sitophilus zeamais and its effectiveness decreased with time. The tested oil was more persistent for inhibiting progeny production than on adult mortality. Further studies are needed to evaluate the quality of treated grains at different storage times.

Botanical insecticides are more biodegradable than synthetic chemicals and could be a source of more environmental-friendly insecticides. Accordingly, the effectiveness of oils from Azadirachta indica seeds and pulverized seeds of this plant and leaf powder of Plectranthus glandulosus were tested against Callosobruchus maculatus on cowpea seeds and Sitophilus zeamais on maize grains at fixed laboratory conditions. The azadirachtin A contents of A. indica seed oils and powders from sun-dried kernels, shade-dried kernels, sun-dried seeds and shade-dried seeds, and the chemical composition of P. glandulosus powders from sun-dried leaves, were determined, before admixing each product with cowpea seeds or maize grains for the toxicity and progeny reduction bioassay studies. Mortality counts were determined after 6 d (C. maculatus) or 7 d (S. zeamais). After the mortality counts, the grains were kept until all the emerging F 1 progeny were recorded. From the results, Azadirachtin A content was higher in A. indica seed oil than in powder. The average content of Azadirachtin A in the seed powder was 1.20 g/kg and this irrespective of the drying regime. On the contrary, the oil from the shade-dried seeds (3.69 g/kg) had a higher azadirachtin A content than that from the sun-dried seeds. About 45 volatile compounds were found in the sun-dried leaves of P. glandulosus. Generally, P. glandulosus powder caused greater mortality to C. maculatus and S. zeamais than A. indica seed powder, but the neem seed oil was more active towards both insects than the powders. The A. indica products were more effective in suppressing progeny emergence in both insects than P. glandulosus leaf powders. Insecticidal products from the present study could form a major component of the integrated storage protection package for cowpea and maize against beetle infestations.

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 aqueous extracts of Azadirachta indica and Boswellia dalzielii, Metarhizium anisopliae, alone and in combination with plant extracts, as well as the commercial insecticide Decis were tested on two Vigna unguiculata varieties in field in two agroecological zones (Guinean Savanah and Sahelian Savanah) of Cameroon. The field trials were arranged in a completely randomized block design with nine treatments including control. Each treatment was replicated four times. Vigna unguiculata plants were sprayed at flowering stage thrice with insecticidal products at 5 days interval. Data assessment consisted of counting ramifications per plant, the number of pods per block, and seed yield. All the tested insecticides significantly (p<0.0001) improved the cowpea yield in the two agro-ecological zones. ...

Resistance of malaria vectors to synthetic chemicals with high operational cost and environmental pollution has been a great challenge to scientists. Alternative approaches such as the use of natural plant products which are environmentally friendly are put in place to control malaria vectors. This study was focused on testing the effectiveness of three solvent extracts of Lantana camara on the 3rd instar larvae and adults of Anopheles gambiae s. l. These extracts were obtained by maceration. Bioassays test were carried out by WHO’s method for determination of larvicidal and adulticidal efficacy. The results show that, larval mortality increased significantly with the concentration and exposure time. Lethal concentrations 50 (LC50) and 95 (LC95) after 24 hours of larvae exposure time are respectively 0.31 g/mL and 1.53 g/mL  while within 48 h they are 0.27 g/mL and 0.79 g/mL for hexane extract; 1.45 g/mL and 2.0 g/mL (24 h exposure), 0.84 g/mL and 1.55 g/mL (48 h exposure) for aceto...

To promote the use of natural substances for better management of the cowpea thrips Megalurothrips sjostedti, the potential of aqueous extract of Azadirachta indica, Boswellia dalzielii and Metarhizium anisopliae, alone and their combinations in comparison with the synthetic chemical insecticide (Decis) were tested. The experiments were carried out in two cowpea varieties under field conditions within the Sudano-Sahelian agro-ecological zone of Cameroon. Trials were arranged in a completely randomized block design with nine treatments. The nine treatments consisted of a negative control, A. indica; B. dalzielii; M. anisopliae, A. indica+B. dalzielii; M. anisopliae+B. dalzielii; M. anisopliae+A. indica; M. anisopliae+A. indica+B. dalzielii and Decis. Each treatment replicated four times. Vigna unguiculata plants were sprayed from flowering stage thrice with insecticidal products at 5 day intervals. The density of adults and larvae thrips was assessed on 5 flowers per block during 5 d...

The Azadirachtin A contents of Azadirachta indica powders from sun-dried kernels, shade-dried kernels, sun-dried seeds and shade-dried seeds, were determined. Cowpea or maize grains were admixed with the powders at the rates 0, 5, 10, 20, 30 and 40 g/kg for the assessment of mortality over a 6-d (Callosobruchus maculatus) or 14-d period (Sitophilus zeamais), as well as for damage and persistence bioassay. Drying regime did not affect the Azadirachtin A amounts in the seeds. All A. indica powders caused a significant dose-dependent mortality to S. zeamais and C. maculatus, as well as completely suppressed progeny production and grain damage. S. zeamais was more susceptible to the powders than C. maculatus. That the bioactivity of powders from sun-dried A. indica seeds were generally similar to those of the shade-dried ones, could speed up processing of seeds by farmers and minimize attacks by fungi which may produce aflatoxins on treated grains.

The response of pests to the effects of a botanical insecticide can vary spatially and temporally. To test whether efficacy of botanicals differed spatially, the insecticidal efficacy of Gnidia kaussiana and Ocimum canum against Callosobruchus maculatus was investigated in two different agroecological zones of Cameroon, i.e. Maroua and Ngaoundéré (sudano-sahelian and sudano

Botanicals could be eco-friendly alternatives to chemical pesticides in stored product protection. Ocimum canum leaf powder was sequentially extracted in hexane, acetone and methanol, and the fractions were tested for their potential in protecting stored Bambara groundnut seeds against the infestation of Callosobruchus maculatus. Bambara groundnut seeds (50 g) were treated with 1 and 5 g/kg of extract to evaluate the repellence, mortality, F1 progeny production, seed damage of the beetle as well the persistence of the test substances. The hexane fraction was more repellent than the other two, recording repellence class V at 1 g/kg. Hexane fraction also showed superior toxicity, causing 100% mortality of C. maculatus at 5 g/kg within 7 days of exposure. All the fractions, at 5 g/kg, somewhat completely inhibited progeny emergence and seed damage. Hexane fraction had sufficient efficacy to be a component of storage pest management package of C. maculatus.

The aim of this study was to determine the insecticidal efficacy of mixture of NeemAzal a commercial neem product and Plectranthus glandulosus leaf powder against Callosubruchus maculatus and Sitophilus zeamais. Mixed at various proportions (100 + 0, 75 + 25, 50 + 50, 25 + 75 and 0 +100%, these powders were tested on adult mortality, inhibition of offspring production and their persistence on C. maculatus and S. zeamais. All the mixed NeemAzal and P. glandulosus caused significant mortality to adult C. maculatus and S. zeamais. No