Three Togolese aromatic plants' essential oils diurnal variations and their insecticidal activities against the dengue vector Aedesaegypti.

The present reported work deals with the ability of Togolese plants' essential oils (EOs) to act as repellents for Aedes aegypti mosquitoes in order to use them as personal protective requirements or actions against mosquito bites and therefore to drastically reduce the risk of contracting dengue or yellow fever. EOs studied here were extracted from dry leaves of Ageratum conyzoides L., Eucalyptus citriodora Hook, and Lantana camara Linn, three plants that were collected at different daytimes (7 a.m., 1 p.m., and 7 p.m.) at various locations in Togo. Using a Clevenger-type device, EOs were obtained by the hydrodistillation method (Clevenger, 1928). The physical parameters of the EOs such as density, refractive index, rotatory power, and organoleptic properties were determined. Then, the characterization of EOs using gas chromatography equipped with a flame ionization detector (GC/FID) and gas chromatography coupled to mass spectrometry (GC/MS) was conducted. Chemical analyses showed the presence of several main compounds from EO samples of the three plants. The major compounds were characterized and identified as: (i) precocene I (67.7, 70.6, and 66.9%) and ß-caryophyllene (17.4, 12.1, and 16.5%) for the EO of A. conyzoïdes; (ii) citronellal (63.3, 67.2, and 75.4%) and citronellol (24.5, 21.4, and 14.3%) for E. citriodora and (iii) ß-caryophyllene (15.3, 11.7, and 12.4%), sabinene (28.4, 35, and 33.3%) and eucalyptol (11.5, 14.1, and 15.6%) for L. camara at 7 a.m., 1 p.m., and 7 p.m., respectively. The yield and the chemical composition of the oils vary according to harvesting time and sunlight. The insecticidal activity of EOs was evaluated following the CDC bottle method on Aedes aegypti females. All the EOs tested on the female adults of Aedes aegypti showed significant insecticidal activity. The EO of A. conyzoïdes at 1 p.m. and 7 p.m. resulted in 100% mortality after 8 min of exposure time at the lowest concentration (0.0025%). At the same concentration for the EO of E. citriodora, the mortality rates were 83%, 38.8%, and 30.80% at 7 a.m., 1 p.m., and 7 p.m., respectively for an exposure time of 8 min. The EO extracted from the leaves of L. camara harvested at 7 a.m. was effective after an exposure time of 15 min for a concentration of 0.02%. For the same concentration, the mortality rates of the EO of L. camara harvested at 1 p.m. and 7 p.m., after 8 min were 62.9% and 52%, respectively. From these interesting results reported for the first time in Togo, EOs from leaves of three Togolese plants harvested at different times of the day appear to be a valuable alternative for mosquito vector control in Togo or abroad countries in which dengue and yellow fever constitute a terrible scourge.

Insecticide resistance intensity and efficacy of synergists with pyrethroids in Anopheles gambiae (Diptera: Culicidae) from Southern Togo.

BACKGROUND: This study was designed to provide insecticide resistance data for decision-making in terms of resistance management plans in Togo. METHODS: The susceptibility status of Anopheles gambiae sensu lato (s.l.) to insecticides used in public health was assessed using the WHO tube test protocol. Pyrethroid resistance intensity bioassays were performed following the CDC bottle test protocol. The activity of detoxification enzymes was tested using the synergists piperonyl butoxide, S.S.S-tributlyphosphorotrithioate and ethacrinic acid. Species-specific identification of An. gambiae s.l. and kdr mutation genotyping were performed using PCR techniques. RESULTS: Local populations of An. gambiae s.l. showed full susceptibility to pirimiphos methyl at Lomé, Kovié, Anié, and Kpèlè Toutou. At Baguida, mortality was 90%, indicating possible resistance to pirimiphos methyl. Resistance was recorded to DDT, bendiocarb, and propoxur at all sites. A high intensity of pyrethroid resistance was recorded and the detoxification enzymes contributing to resistance were oxidases, esterases, and glutathione-s-transferases based on the synergist tests. Anopheles gambiae sensu stricto (s.s.) and Anopheles coluzzii were the main species identified. High kdr L1014F and low kdr L1014S allele frequencies were detected at all localities. CONCLUSION: This study suggests the need to reinforce current insecticide-based malaria control interventions (IRS and LLINs) with complementary tools.

Insecticide resistance profiles of Anopheles gambiae s.l. in Togo and genetic mechanisms involved, during 3-year survey: is there any need for resistance management?

BACKGROUND: Malaria, one of the world's greatest public health challenges, is an endemic disease with stable transmission in Togo. Combating malaria requires an effective vector control. This study provides temporal data on insecticide resistance status in the major malaria vector Anopheles gambiae sensu lato (s.l.) from Togo. METHODS: Two to 5 days old females of An. gambiae s.l., originating from three localities (Baguida, Kovié, Kolokopé) were subjected to insecticide-impregnated papers during 3 years (2012, 2013, 2016) as follows: organochlorides (4% DDT), pyrethroids (0.05% deltamethrin, 0.75% permethrin, 0.05% lambdacyhalothrin), carbamates (0.4% bendiocarb and 0.1% propoxur), and organophosphates (5% malathion, 0.4% chlorpyrifos methyl, 1% fenitrothion) following the WHO standard protocol. Dead and surviving mosquitoes were stored separately in Eppendorf tubes containing silica gel for DNA extraction, species identification, and kdr and ace-1 genotyping. RESULTS: Knockdown times (KDT50 and KDT95) were high in An. gambiae s.l. The lowest KDTs were recorded at Baguida in 2013 for deltamethrin (KDT50 = 24.7, CI [22.4-27.12] and KDT95 = 90.78, CI [76.35-113.49]). No KDTs were recorded for DDT and in some instances for permethrin. In general, An. gambiae s.l. was resistant to most of the four classes of insecticides during the survey periods regardless of locality and year, except to chlorpyrifos methyl. In some instances, mosquitoes were fully susceptible to fenitrothion (Kolokopé: 100% and Kovié: 98.05%, CI [95.82-100.26]) and malathion (100% at both Kolokopé and Kovié) in 2013, and malathion only (Kolokopé; 100%) in 2016. Anopheles coluzzii, An. gambiae and Anopheles arabiensis were the three sibling species identified at the three localities with some hybrids at Baguida (2013), and Kovié (2012 and 2016), respectively. Anopheles gambiae was relatively dominant (61.6%). The kdr 1014F allele frequency was > 0.9 in most of the cases, except at Kolokopé (f (1014F) = 0.63, CI [0.55-0.71]) in 2013. The kdr 1014S allele frequency was below 0.02. The highest ace-1 frequencies were identified in An. gambiae at Baguida (2012: 0.52, CI [0.34-0.69] and 2013: 0.66, CI [0.46-0.86]). CONCLUSION: The resistance status is worrying in Togo and should be considered in future malaria vector resistance management programmes by decision-makers.

Efficacy of two PBO long lasting insecticidal nets against natural populations of Anopheles gambiae s.l. in experimental huts, Kolokopé, Togo.

LLINs containing an insecticide plus the synergist, piperonyl butoxide (PBO) have been designed for increased efficacy against pyrethroid-resistant malaria vectors. In this study, two LLINs with PBO, PermaNet® 3.0 and Olyset® Plus, and a pyrethroid-only LLIN, Yorkool®, were evaluated in experimental huts against a free-flying, wild population of Anopheles gambiae s.l. in Kolokopé, a cotton cultivated area of Togo. WHO susceptibility tube tests and subsequent molecular assays determine the An. gambiae s.l. populations to be resistant to pyrethroids and DDT with both target site kdr and metabolic resistance mechanisms involved in the resistance observed. Anopheles gambiae s.s. and An. coluzzi were present in sympatry though the kdr (L1014F) mutation was observed at a higher frequency in An. gambiae s.s. The experimental hut results showed that both PermaNet® 3.0 and Olyset® Plus nets induced similar levels of deterrence, exophily, and reduced blood feeding rate against wild An. gambiae s.l. in contrast to the pyrethroid only LLIN, Yorkool®. The proportion of wild An. gambiae s.l. killed by unwashed PermaNet® 3.0 was significantly higher than unwashed Olyset® Plus (corrected mortality 80.5% compared to 66.6%). Similar blood feeding inhibition rates were observed for unwashed PermaNet® 3.0 and Olyset® Plus; however, PermaNet® 3.0 washed 20 times demonstrated significantly higher blood feeding inhibition rate than Olyset® Plus washed 20 times (91.1% compared with 85.6% respectively). Yorkool® performed the worst for all the parameters evaluated. In an area of pyrethroid resistance of An. gambiae s.l involving kdr target site and metabolic resistance mechanisms, LLINs with PBO can provide additional protection in terms of reduction in blood feeding and increase in mosquito mortality compared to a pyrethroid-only net, and should be considered in malaria vector control strategies.