Insecticidal Activity of Local Plants Essential Oils Against Laboratory and Field Strains of Anopheles gambiae s. l. (Diptera: Culicidae) From Burkina Faso.

The emergence and intensification of resistance to insecticides in malaria vector populations is the main obstacle to insecticide-based control efforts. The main objective of this study was to evaluate the larvicidal and adulticidal properties of the essential oils (EOs) of Ocimum canum, Hyptis suaveolens, Hyptis spicigera, and Lantana camara on field-collected, pyrethroids-resistant mosquitoes, local laboratory strains, and susceptible 'Kisumu' strain of Anopheles gambiae (Meigen) (Diptera: Culicidae) populations. Larvae and adults of these mosquitoes were challenged against four EOs. The mortality rates of larvae and adults were assessed 24 h after exposure to the EOs. Species identifications and detection of the L1014F and L1014S kdr mutations and the 1575Y super-kdr mutation were carried out using polymerase chain reaction on the pyrethroid-resistant mosquitoes from the field. EO compositions were analyzed by gas chromatography and mass spectrometry. Monoterpene hydrocarbons were the major components of H. suaveolens and H. spicigera EOs (49.8%) and (69.6%), respectively, whereas oxygenated monoterpenes (68.7%) were predominant in the O. canum EO. For L. camara, the component yields were variable, but it was the most effective EO against all strains. The LC50 values for the larvae were 7.73 and 25.63 ppm for the susceptible 'Kisumu' and resistant field strains, respectively. The LC50 for adults was 0.24% for the susceptible strain and 1.98% for the resistant strain. Molecular analysis confirmed the presence of L1014F and N1575Y mutations in resistant Anopheles arabiensis and Anopheles coluzzii mosquitoes from the field. Our results highlighted the potential of the EOs of local plants as insecticides against resistant and susceptible strains of An. gambiae populations.

Potential of Botanicals to Control Callosobruchus maculatus (Col.: Chrysomelidae, Bruchinae), a Major Pest of Stored Cowpeas in Burkina Faso: A Review.

Cowpea is an essential food legume in the tropics and particularly for sub-Saharan African populations. Postharvest grain storage, however, is a major constraint for crop expansion and year-round availability due to the cowpea weevil, Callosobruchus maculatus F., the main storage pest of cowpeas in West Africa. The use of chemicals for cowpea storage is a common practice which represents, however, a risk for consumers, environment, and could also exacerbate pest control. In Burkina Faso, since the early 2000s, several scientific investigations have focused on the control of C maculatus using botanicals considered as promising and safe alternatives to chemicals. The aim of this review is to take stock of the research conducted and to identify the potential candidates on which future studies in this field will focus. The set of data analyzed show that several plants materials, including powders, crushed plants and essential oils (EO), were active against eggs, larvae, and adults of C maculatus, through dose-dependent mortality responses. However, EO extracted from native aromatic plants have yielded the most promising results, specifically EO from Ocimum canum appeared as the best candidate control agent. Other potentially interested EO tested included Hyptis suaveolens, Hyptis spicigera, and Lippia multiflora. Based on these results, attempts to optimize the use of EO for cowpea storage were conducted in laboratory and field conditions. Side effects of botanicals toward the main biological control agent, the ectoparasitoid Dinarmus basalis have also been highlighted. The results are discussed in a view of practical use of botanicals and EO as safe alternatives for Integrated Pest Management in stored cowpeas in Africa and developing countries.

Susceptibility of MED-Q1 and MED-Q3 Biotypes of Bemisia tabaci (Hemiptera: Aleyrodidae) Populations to Essential and Seed Oils.

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a major pest of many agricultural and ornamental crops in tropical and subtropical regions causing damages that result in important economic losses. Insecticides are commonly used in greenhouses or fields to control B. tabaci populations leading to rapid evolution of resistance that render treatments inefficient. Therefore, and for environmental and human health concerns, other approaches must be developed for this pest management. In the present study, we compare, using the leaf dip method, the toxicity of three essential oils (Cymbopogon citratus, Ocimum americanum, and Hyptis spicigera) and three seed oils (Lannea microcarpa, Lannea acida, and Carapa procera) with three chemical insecticides (acetamiprid, deltamethrin, and chlorpyrifos-ethyl) on adults. Two B. tabaci biotypes (MED-Q1 and MED-Q3) belonging to the Mediterranean species and collected in Burkina Faso were used. Essential oils were analyzed by gas chromatography-mass spectrometry and gas chromatography-flame ionization detector. We showed that these two biotypes have different levels of resistance to the three insecticides, MED-Q3 being more sensitive than MED-Q1. Moreover, they differ in the frequency of resistance alleles to insecticides, especially for organophosphates, as these alleles are almost fixed in MED-Q1. On the other hand, the two biotypes prove to be more susceptible to the plant extracts than to insecticides except for chlorpyrifos-ethyl, with essential oils that showed the highest insecticidal activities. Monoterpenes content were the most abundant and showed the highest insecticidal activities. Our results indicated that essential oils, but also seed oils, have the potential to constitute an alternative strategy of pest management.

Composition and antimicrobial activities of Lippia multiflora Moldenke, Mentha x piperita L. and Ocimum basilicum L. essential oils and their major monoterpene alcohols alone and in combination.

Essential oils from leaves of Lippia multiflora, Mentha x piperita and Ocimum basilicum from Burkina Faso were analysed by GC-FID and GC-MS. Major components were p-cymene, thymol, b-caryophyllene, carvacrol and carvone for L. multiflora, menthol and iso-menthone for M. x piperita and, linalool and eugenol for O. basilicum. The essential oils and their major monoterpene alcohols were tested against nine bacterial strains using the disc diffusion and broth microdilution methods. The essential oils with high phenolic contents were the most effective antimicrobials. The checkerboard method was used to quantify the efficacy of paired combinations of essential oils and their major components. The best synergetic effects among essential oils and major components were obtained with combinations involving O. basilicum essential oil and eugenol, respectively. As phenolic components are characterized by a strong spicy aroma, this study suggests that the selection of certain combinations of EOs could help to reduce the amount of essential oils and consequently reduce any adverse sensory impact in food.

Mass spectra of 1,3,5-triarylpentane-1, 5-diones: formation and decomposition of pyrilium cation from the molecular ion.

Electron impact mass spectra of 1,3,5-triarylpentane-1,5-diones are reported. All compounds studied show a tendency to eliminate a water molecule and also the elements of [H3O] before fragmentation to smaller ions. The [H3O] loss proceeds via loss of water to form a pyran ion, which subsequently eliminates a hydrogen atom to form the stable pyrillium cation.