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<front>
<journal-meta>
<journal-id journal-id-type="publisher-id">Front. Trop. Dis</journal-id>
<journal-title>Frontiers in Tropical Diseases</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Trop. Dis</abbrev-journal-title>
<issn pub-type="epub">2673-7515</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.3389/fitd.2022.853405</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Tropical Diseases</subject>
<subj-group>
<subject>Original Research</subject>
</subj-group>
</subj-group>
</article-categories>
<title-group>
<article-title>Essential Oils From Five Local Plants: An Alternative Larvicide for <italic>Anopheles gambiae</italic> s.l. (Diptera: Culicidae) and <italic>Aedes aegypti</italic> (Diptera: Culicidae) Control in Western Burkina Faso</article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Balbon&#xe9;</surname>
<given-names>Mahamoudou</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/1723732"/>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Soma</surname>
<given-names>Dieudonn&#xe9; Diloma</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Namountougou</surname>
<given-names>Moussa</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Drabo</surname>
<given-names>Samuel Fogn&#xe9;</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Konat&#xe9;</surname>
<given-names>Hamadou</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Toe</surname>
<given-names>Oumarou</given-names>
</name>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Bayili</surname>
<given-names>Koama</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Meda</surname>
<given-names>Georges Benson</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author">
<name>
<surname>Dabir&#xe9;</surname>
<given-names>Roch Kounbobr</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/637274"/>
</contrib>
<contrib contrib-type="author" corresp="yes">
<name>
<surname>Gnankine</surname>
<given-names>Olivier</given-names>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="author-notes" rid="fn001">
<sup>*</sup>
</xref>
<uri xlink:href="https://loop.frontiersin.org/people/637509"/>
</contrib>
</contrib-group>
<aff id="aff1">
<sup>1</sup>
<institution>Laboratoire d&#x2019;Entomologie Fondamentale et Appliqu&#xe9;e, Unit&#xe9; de Formation et de Recherche en Sciences de la Vie et de la Terre (UFR-SVT), Universit&#xe9; Joseph KI-ZERBO</institution>, <addr-line>Ouagadougou</addr-line>, <country>Burkina Faso</country>
</aff>
<aff id="aff2">
<sup>2</sup>
<institution>Institut de Recherche en Sciences de la Sante&#xb4; /Centre Muraz, D&#xe9;partement d'Entomologie M&#xe9;dicale</institution>, <addr-line>Bobo-Dioulasso</addr-line>, <country>Burkina Faso</country>
</aff>
<aff id="aff3">
<sup>3</sup>
<institution>Universite Nazi Boni, Institut des Sciences de la Sant&#xe9;</institution>, <addr-line>Bobo-Dioulasso</addr-line>, <country>Burkina Faso</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>Edited by: Cleber Galv&#xe3;o, Oswaldo Cruz Foundation (Fiocruz), Brazil</p>
</fn>
<fn fn-type="edited-by">
<p>Reviewed by: Carlos Manuel Dutok-S&#xe1;nchez, Universidade Federal do Amap&#xe1;, Brazil; Sarita Kumar, University of Delhi, India; Paloma Mendon&#xe7;a, University of Vassouras, Brazil</p>
</fn>
<fn fn-type="corresp" id="fn001">
<p>*Correspondence: Olivier Gnankine, <email xlink:href="mailto:olignankine@gmail.com">olignankine@gmail.com</email></p>
</fn>
<fn fn-type="other" id="fn002">
<p>This article was submitted to Vector Biology, a section of the journal Frontiers in Tropical Diseases</p>
</fn>
</author-notes>
<pub-date pub-type="epub">
<day>06</day>
<month>07</month>
<year>2022</year>
</pub-date>
<pub-date pub-type="collection">
<year>2022</year>
</pub-date>
<volume>3</volume>
<elocation-id>853405</elocation-id>
<history>
<date date-type="received">
<day>12</day>
<month>01</month>
<year>2022</year>
</date>
<date date-type="accepted">
<day>30</day>
<month>03</month>
<year>2022</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2022 Balbon&#xe9;, Soma, Namountougou, Drabo, Konat&#xe9;, Toe, Bayili, Meda, Dabir&#xe9; and Gnankine</copyright-statement>
<copyright-year>2022</copyright-year>
<copyright-holder>Balbon&#xe9;, Soma, Namountougou, Drabo, Konat&#xe9;, Toe, Bayili, Meda, Dabir&#xe9; and Gnankine</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<abstract>
<sec>
<title>Introduction</title>
<p>Malaria and dengue are two main vector-borne infectious diseases transmitted by <italic>Anopheles gambiae</italic> and <italic>Aedes aegypti</italic>, respectively, in tropical and subtropical regions. The concern for environmental safety and the increasing development of resistance to the chemical in main arthropod vectors raises interest in the search for botanicals such as essential oils (EOs) that can be used in vector control.</p>
</sec>
<sec>
<title>Methods</title>
<p>Larvicidal bioassays were performed according to the WHO standard methods using <italic>Ae. aegypti</italic> and <italic>An. gambiae</italic> larvae collected from Bobo-Dioulasso and in the Kou Valley (VK), respectively, two areas located in Houet Province of western Burkina Faso. Kisumu and Bora bora, the susceptible strains of <italic>An. gambiae</italic> and <italic>Ae. aegypti</italic>, respectively, were used as controls. OEs extracted from leaves of five aromatic plants, <italic>Cymbopogon citratus</italic>, <italic>Cymbopogon nardus</italic>, <italic>Eucalyptus camaldulensis</italic>, <italic>Lippia multiflora</italic>, and <italic>Ocimum americanum</italic>, naturally growing in Burkina Faso were tested. The pyriproxyfen was used as a positive control.</p>
</sec>
<sec>
<title>Results</title>
<p>As a result, the lethal concentrations (LC<sub>50</sub>) for <italic>Ae. aegypti</italic> from Bobo-Dioulasso and <italic>An. gambiae</italic> from VK ranged from 41.9 to 103.8 ppm and 39.5 to 138.1 ppm, respectively. As for LC<sub>90</sub> values, they ranged from 74.6 to 311.3 ppm for <italic>Ae. aegypti</italic> from Bobo-Dioulasso and from 90.2 to 328.9 ppm for <italic>An. gambiae</italic> from VK. Among the EOs tested, <italic>L. multiflora</italic> showed the highest activity against all the strains of <italic>An. gambiae</italic> and <italic>Ae. aegypti</italic> larvae. No difference in terms of LC<sub>50</sub> values was found between <italic>L. multiflora</italic> and pyriproxyfen used as a positive control on <italic>An. gambiae</italic> larvae. It is not the case for <italic>Aedes aegypti</italic> populations, where pyriproxyfen remains the most toxic. Overall, <italic>An. gambiae</italic> populations were the most susceptible to EOs tested as compared to <italic>Ae. aegypti</italic> populations.</p>
</sec>
<sec>
<title>Conclusion</title>
<p>Our study furthers our knowledge of the larvicidal activity of EOs in the western part of Burkina and opens new avenues in their putative use in vector control strategies.</p>
</sec>
</abstract>
<kwd-group>
<kwd>resistance</kwd>
<kwd>essential oils</kwd>
<kwd>larvicidal activities</kwd>
<kwd>lethal concentration</kwd>
<kwd>Bobo-Dioulasso</kwd>
</kwd-group>
<counts>
<fig-count count="0"/>
<table-count count="5"/>
<equation-count count="0"/>
<ref-count count="33"/>
<page-count count="7"/>
<word-count count="3981"/>
</counts>
</article-meta>
</front>
<body>
<sec id="s1">
<title>Background</title>
<p>Vector-borne diseases are human diseases caused by parasites, viruses, or bacteria transmitted by vectors. Each year, more than 700,000 deaths occur worldwide due to vector-borne diseases such as dengue, yellow fever, Japanese encephalitis, leishmaniasis, Chagas disease, onchocerciasis, malaria, schistosomiasis, and human African trypanosomiasis (<xref ref-type="bibr" rid="B1">1</xref>). Among these diseases, malaria remains the most serious vector-borne disease, affecting between 300 and 500 million people, and 1.4 to 2.6 million deaths annually throughout the world were recorded. More than 40% of the world&#x2019;s population lives in malarious areas (<xref ref-type="bibr" rid="B2">2</xref>).</p>
<p>According to the epidemiological bulletin, in the first half of 2018, Burkina Faso recorded 3,501,245 cases of malaria, including 1,002 deaths, for a case-fatality rate of 0.7% (<xref ref-type="bibr" rid="B3">3</xref>). The same is true for dengue, where the number of reported cases worldwide peaked in 2019, and all WHO regions were affected (<xref ref-type="bibr" rid="B4">4</xref>). In Burkina Faso, an increase in the weekly incidence of dengue cases was noted from week 31 of the year 2017 (<xref ref-type="bibr" rid="B5">5</xref>).</p>
<p>Current mosquito control strategies depend primarily on chemical insecticides. The discovery, development, and use of chemicals have reduced the interest in plant products. However, widespread use of these insecticides in public health and agriculture for the control of vector and pest species has favored many concerns such as the increasing physiological resistance in major vector species, environmental pollution, and toxic hazards to human and other non-target organisms due to their broad spectrum of activity (<xref ref-type="bibr" rid="B6">6</xref>&#x2013;<xref ref-type="bibr" rid="B9">9</xref>). As a result, there has been an increased interest in developing potential alternative or additional control methods/tools that are effective against the target vector species, which are environmentally safe, biodegradable, and low cost and can be used by individuals and communities in specific situations (<xref ref-type="bibr" rid="B10">10</xref>, <xref ref-type="bibr" rid="B11">11</xref>). Therefore, in recent years, various workers have been concentrating their efforts on the search for natural products derived from plants as an alternative to conventional insecticides used in controlling vectors for which resistance was detected (<xref ref-type="bibr" rid="B12">12</xref>). Among many natural products, essential oils (EOs) and their constituents have received considerable attention in the search for new pesticides and have been found to possess an insecticidal potential (<xref ref-type="bibr" rid="B13">13</xref>).</p>
<p>EOs show several interesting properties. First, they easily penetrate insect cuticles, which increases their bioavailability (<xref ref-type="bibr" rid="B14">14</xref>). This property could be of interest if it results in a shortened stay of insects on treated surfaces. Second, EO compounds such as acyclic or monocyclic monoterpenes are small and volatile molecules that might have spatial repellency properties. For example, insect sensilla are specialized for detecting odorants and have been shown to respond to volatile monoterpenes (<xref ref-type="bibr" rid="B14">14</xref>). Finally, active compounds in EOs may have a specific mode of action, which makes them good alternatives to the use of pyrethroids.</p>
<p>The EO of <italic>Lippia multiflora</italic> is used as a spice, a meal condiment, a drink flavoring (<xref ref-type="bibr" rid="B15">15</xref>), and a mouthwash. In addition to insecticidal activities, Abena et&#xa0;al. (<xref ref-type="bibr" rid="B16">16</xref>) found analgesic, antipyretic, and anti-inflammatory effects of <italic>L. multiflora</italic> oil. <italic>Cymbopogon citratus</italic> EO has antimicrobial activity against <italic>Helicobacter pylori</italic>, a bacterium responsible for gastroduodenal diseases (<xref ref-type="bibr" rid="B17">17</xref>). <italic>Cymbopogon nardus</italic> is a medicinal plant because of its analgesic effect and is widely used in gastronomy (<xref ref-type="bibr" rid="B18">18</xref>). Also, several studies noticed the insecticidal properties of EO of <italic>C. nardus</italic>, <italic>C. citratus</italic>, <italic>Ocimum americanum</italic>, and <italic>Eucalyptus camaldulensis</italic> (<xref ref-type="bibr" rid="B18">18</xref>&#x2013;<xref ref-type="bibr" rid="B21">21</xref>).</p>
<p>In Burkina Faso, some studies on the insecticidal effects of EOs with mosquitoes in general and mosquito larvae in particular have involved strains restricted to Ouagadougou (<xref ref-type="bibr" rid="B21">21</xref>&#x2013;<xref ref-type="bibr" rid="B23">23</xref>). Little is known about the EO susceptibility in <italic>Anopheles</italic> and <italic>Aedes</italic> populations in the western part of this country. Moreover, previous studies did not take into account the positive control in the various tests.</p>
<p>Our study aimed at evaluating the larvicidal activities of EOs of five local aromatic plants from Burkina Faso, including <italic>C. citratus</italic>, <italic>C. nardus</italic> (DC.) Stapf, <italic>E. camaldulensis</italic> Dehn, <italic>L. multiflora</italic>, and <italic>O. americanum</italic> (Wild.) A.J. Paton in terms of lethal concentrations (LC<sub>50</sub> and LC<sub>90</sub>) upon field populations of <italic>Aedes aegypti</italic> from Bobo-Dioulasso and <italic>Anopheles gambiae</italic> from the Vall&#xe9;e du Kou (VK).</p>
</sec>
<sec id="s2">
<title>Material and Methods</title>
<sec id="s2_1">
<title>Mosquito Larval Collection and Rearing</title>
<p>
<italic>An. gambiae</italic> larvae were collected from district number 7 of the Vall&#xe9;e du Kou (Bama) (11&#xb0;24&#x2032;N and 4&#xb0;24&#x2032;O), a rice-growing area located 30&#xa0;km north of Bobo-Dioulasso. <italic>Ae. aegypti</italic> larvae were collected from tires in various urban settings in Bobo-Dioulasso, the economic capital city of Burkina Faso. Bobo-Dioulasso and Bama are two localities in the province of Houet in western Burkina Faso. The larvae were collected from June to October 2021 and transported to the insectary of the Institute of Research in Health Sciences (IRSS) located in Bobo-Dioulasso where 3 and 4 larval instars were sorted according to Filho (<xref ref-type="bibr" rid="B24">24</xref>). Larvae from laboratory reference strains were used as controls. The insectary conditions were 27&#xb0;C &#xb1; 2&#xb0;C temperature, 80% &#xb1; 10% relative humidity, and 12-h light and 12-h dark photoperiod.</p>
</sec>
<sec id="s2_2">
<title>Plant Materials and Essential Oil Procurement</title>
<p>The five plant species tested, <italic>C. citratus</italic>, <italic>C. nardus</italic> (Linn.), <italic>E. camaldulensis</italic>, <italic>L. multiflora</italic>, and <italic>O. americanum</italic>, were used in this current study. They were chosen firstly due to endogenous data provided from informants questioned in areas investigated as well as the data from the literature. These plants were collected from the garden of the Research Institute of Applied Sciences and Technologies (IRSAT). The identification of the plants and extraction of EOs were performed by IRSAT. All the EOs were extracted from the leaves of the test plants by hydrodistillation (HD) using a <italic>clevenger</italic>-type apparatus and stored in a dark glass bottle at 4&#xb0;C prior to use. The oils thus obtained were separated from water in the condenser and stored in airtight containers under refrigeration (4&#xb0;C) till their later use for larval bioassays. The major compounds of these EOs were obtained by gas chromatography&#x2013;mass spectrometry (GC-MS).</p>
</sec>
<sec id="s2_3">
<title>Larvicidal Bioassays in the Laboratory</title>
<p>The larval bioassay tests were carried out following the standard WHO larval bioassay test method (<xref ref-type="bibr" rid="B25">25</xref>). They were carried out in the laboratory of the Institute of Research in Health Sciences located in Bobo-Dioulasso. Clear plastic cups with capacities of 200&#xa0;ml each were used for the larvicidal bioassays. An appropriate amount of each EO was dissolved in acetone to prepare 1&#xa0;ml of stock solution. Fresh stock solutions of each of the above stock solutions were prepared by adding distilled water to produce the required concentrations (50, 100, 150, and 200 ppm). Four replicates were carried out for each test concentration and species of mosquito larvae. Twenty active third and fourth larval instars of <italic>An. gambiae</italic> and <italic>Ae. aegypti</italic> in 10&#xa0;ml of distilled water were transferred into each clear plastic cup that contained 139&#xa0;ml of distilled water. One milliliter of the mixing solution of EO and acetone was added to each cup that contained 149&#xa0;ml of distilled water to give a final solution of 150&#xa0;ml with the desired concentrations. Two replicates of the control were carried out simultaneously with 149&#xa0;ml of distilled water and 1&#xa0;ml of acetone. Pyriproxyfen, the reference chemical larvicidal, was used at different concentrations as a positive control.</p>
</sec>
<sec id="s2_4">
<title>Data Analysis</title>
<p>Analyses were performed by using the statistical software XLSTAT version 2,015.1.01. The LC<sub>50</sub>, LC<sub>90</sub>, and the 95% CIs were calculated by probit analysis using the same statistical software in order to compare the larvicidal potency of the plants and susceptibility of the test mosquito larvae. LC<sub>50</sub> and LC<sub>90</sub> values were judged as significantly different between the EOs (p &lt; 0.05) if the CIs did not overlap (<xref ref-type="bibr" rid="B14">14</xref>, <xref ref-type="bibr" rid="B26">26</xref>). In all the tests, no control mortality was detected after the 24-h exposure; hence, no correction was required based on Abbot&#x2019;s formula.</p>
</sec>
</sec>
<sec id="s3" sec-type="results">
<title>Results</title>
<sec id="s3_1">
<title>Chemical Characterization of the Essential Oils</title>
<p>The major compounds of the 5 EOs are summarized in <xref ref-type="table" rid="T1">
<bold>Table&#xa0;1</bold>
</xref>. The EO of <italic>C. citratus</italic> was found to be rich in geranial (48.1%), neral (35.8%), and myrcene (11%). The EO of <italic>C. nardus</italic> was predominantly composed of citronellal (41.7%), geraniol (20.8%), and &#x3b2;-elemene (11%). The EO of <italic>E. camaldulensis</italic> was rich in 1,8-cineole (59.5%) and &#x3b1;-pinene (9.17%). The OE of <italic>L. multiflora</italic> was characterized by <italic>p</italic>-cymene (25.27%), &#x3b2;-caryophyllene (12.7%), and thymol (11.88%). <italic>O. americanum</italic> EO was characterized by a high percentage of 1,8-cineole (31.22%) followed by camphor (12.73%).</p>
<table-wrap id="T1" position="float">
<label>Table&#xa0;1</label>
<caption>
<p>Major compounds of the 5 essential oils tested on larvae of <italic>Anopheles gambiae</italic> and <italic>Aedes aegypti</italic>.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Essential oils</th>
<th valign="top" align="center">Major compounds</th>
<th valign="top" align="center">Retention time (min)</th>
<th valign="top" align="center">Percentage (%)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" rowspan="3" align="left">
<italic>Cymbopogon citratus</italic>
</td>
<td valign="top" align="left">Geranial</td>
<td valign="top" align="center">21.181</td>
<td valign="top" align="center">48.1</td>
</tr>
<tr>
<td valign="top" align="left">Neral</td>
<td valign="top" align="center">21.130</td>
<td valign="top" align="center">35.8</td>
</tr>
<tr>
<td valign="top" align="left">Myrcene</td>
<td valign="top" align="center">12.481</td>
<td valign="top" align="center">11</td>
</tr>
<tr>
<td valign="top" rowspan="3" align="left">
<italic>Cymbopogon nardus</italic>
</td>
<td valign="top" align="left">Citronellal</td>
<td valign="top" align="center">18.994</td>
<td valign="top" align="center">41.7</td>
</tr>
<tr>
<td valign="top" align="left">Geraniol</td>
<td valign="top" align="center">22.121</td>
<td valign="top" align="center">20.8</td>
</tr>
<tr>
<td valign="top" align="left">&#x3b2;-Elemene</td>
<td valign="top" align="center">24.880</td>
<td valign="top" align="center">11</td>
</tr>
<tr>
<td valign="top" rowspan="2" align="left">
<italic>Eucalyptus camaldulensis</italic>
</td>
<td valign="top" align="left">1,8-Cineol</td>
<td valign="top" align="center">14.022</td>
<td valign="top" align="center">59.55</td>
</tr>
<tr>
<td valign="top" align="left">&#x3b1;-Pinene</td>
<td valign="top" align="center">10.505</td>
<td valign="top" align="center">9.17</td>
</tr>
<tr>
<td valign="top" rowspan="3" align="left">
<italic>Lippia multiflora</italic>
</td>
<td valign="top" align="left">
<italic>p</italic>-Cymene</td>
<td valign="top" align="center">13.740</td>
<td valign="top" align="center">25.27</td>
</tr>
<tr>
<td valign="top" align="left">&#x3b2;-Caryophyllene</td>
<td valign="top" align="center">25.116</td>
<td valign="top" align="center">12.70</td>
</tr>
<tr>
<td valign="top" align="left">Thymol</td>
<td valign="top" align="center">21.791</td>
<td valign="top" align="center">11.88</td>
</tr>
<tr>
<td valign="top" rowspan="2" align="left">
<italic>Ocimum americanum</italic>
</td>
<td valign="top" align="left">1,8-Cineol</td>
<td valign="top" align="center">14.022</td>
<td valign="top" align="center">31.22</td>
</tr>
<tr>
<td valign="top" align="left">Camphor</td>
<td valign="top" align="center">17.733</td>
<td valign="top" align="center">12.73</td>
</tr>
</tbody>
</table>
</table-wrap>
</sec>
<sec id="s3_2">
<title>Larvicidal Activities of Essential Oils Against <italic>Anopheles gambiae</italic>
</title>
<p>EOs from 5 plant species demonstrated larvicidal activities against susceptible strains and field-collected 3 and 4 larval instars of <italic>An. gambiae</italic>. Overall, five EOs were the most toxic on 3 and 4 larval instars of <italic>An. gambiae</italic> susceptible strain. On the susceptible strain larvae of <italic>An. gambiae</italic> (Kisumu), the LC<sub>50</sub> and LC<sub>90</sub> values were from 3.9 to 75.8 ppm and from 29.5 to 193.5 ppm, respectively (<xref ref-type="table" rid="T2">
<bold>Table&#xa0;2</bold>
</xref>). On field-collected larvae of <italic>An. gambiae</italic> (VK), the LC<sub>50</sub> and LC<sub>90</sub> values were between 39.5 to 138.1 ppm and from 90.2 to 328.9 ppm, respectively (<xref ref-type="table" rid="T3">
<bold>Table&#xa0;3</bold>
</xref>).</p>
<table-wrap id="T2" position="float">
<label>Table&#xa0;2</label>
<caption>
<p>Median and 90% lethal concentrations and their Confidence Limits (CLs) of plant essential oils against 3 and 4 larval instars of <italic>Anopheles gambiae</italic> susceptible strain from Kisumu.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Treatment</th>
<th valign="top" align="center">LC<sub>50</sub> (ppm)</th>
<th valign="top" align="center">Confidence limit 95%</th>
<th valign="top" align="center">LC<sub>90</sub> (ppm)</th>
<th valign="top" align="center">Confidence limit 95%</th>
<th valign="top" align="center">X<sup>2</sup>(df)</th>
<th valign="top" align="center">Slope ( &#xb1; SE)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">Pyriproxyfen</td>
<td valign="top" align="center">3.4<sup>a</sup>
</td>
<td valign="top" align="center">0.8&#x2013;5.8</td>
<td valign="top" align="center">13.6<sup>a</sup>
</td>
<td valign="top" align="center">9.5&#x2013;18.4</td>
<td valign="top" align="center">16.6</td>
<td valign="top" align="center">2.2 &#xb1; 0.52</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Cymbopogon citratus</italic>
</td>
<td valign="top" align="center">49.1<sup>c</sup>
</td>
<td valign="top" align="center">42.1&#x2013;54.8</td>
<td valign="top" align="center">87.6<sup>c</sup>
</td>
<td valign="top" align="center">78.2&#x2013;102.9</td>
<td valign="top" align="center">53.6</td>
<td valign="top" align="center">5.0 &#xb1; 0.69</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Cymbopogon nardus</italic>
</td>
<td valign="top" align="center">30.7<sup>b</sup>
</td>
<td valign="top" align="center">17.9&#x2013;40.0</td>
<td valign="top" align="center">74.7<sup>c</sup>
</td>
<td valign="top" align="center">63.1&#x2013;90.8</td>
<td valign="top" align="center">26.4</td>
<td valign="top" align="center">3.3 &#xb1; 0.64</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Ocimum americanum</italic>
</td>
<td valign="top" align="center">75.8<sup>d</sup>
</td>
<td valign="top" align="center">65.4&#x2013;85.5</td>
<td valign="top" align="center">193.5<sup>d</sup>
</td>
<td valign="top" align="center">164.6&#x2013;244.4</td>
<td valign="top" align="center">74.8</td>
<td valign="top" align="center">3.1 &#xb1; 0.36</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Lippia multiflora</italic>
</td>
<td valign="top" align="center">3.9<sup>a</sup>
</td>
<td valign="top" align="center">1.5&#x2013;6.6</td>
<td valign="top" align="center">29.5<sup>b</sup>
</td>
<td valign="top" align="center">22.0&#x2013;40.8</td>
<td valign="top" align="center">38.5</td>
<td valign="top" align="center">1.4 &#xb1; 0.23</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Eucalyptus camaldulensis</italic>
</td>
<td valign="top" align="center">29.4<sup>b</sup>
</td>
<td valign="top" align="center">15.6&#x2013;40.1</td>
<td valign="top" align="center">90.3<sup>c</sup>
</td>
<td valign="top" align="center">75.3&#x2013;113.1</td>
<td valign="top" align="center">27.4</td>
<td valign="top" align="center">2.6 &#xb1; 0.50</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>LC (lethal concentration) in ppm (part per million). LC values followed by different letters are significantly different.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<table-wrap id="T3" position="float">
<label>Table&#xa0;3</label>
<caption>
<p>Median and 90% lethal concentrations and their Confidence Limits (CLs) of plant essential oils against 3 and 4 larval instars of <italic>Anopheles gambiae</italic> from VK, field strain.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Treatment</th>
<th valign="top" align="center">LC<sub>50</sub> (ppm)</th>
<th valign="top" align="center">Confidence limit 95%</th>
<th valign="top" align="center">LC<sub>90</sub> (ppm)</th>
<th valign="top" align="center">Confidence limit 95%</th>
<th valign="top" align="center">X<sup>2</sup>(df)</th>
<th valign="top" align="center">Slope ( &#xb1; SE)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">Pyriproxyfen</td>
<td valign="top" align="center">23.7<sup>a</sup>
</td>
<td valign="top" align="center">9.3&#x2013;35.5</td>
<td valign="top" align="center">83.3<sup>a</sup>
</td>
<td valign="top" align="center">66.6&#x2013;106.2</td>
<td valign="top" align="center">11.5</td>
<td valign="top" align="center">1.4 &#xb1; 0.41</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Cymbopogon citratus</italic>
</td>
<td valign="top" align="center">138.1<sup>c</sup>
</td>
<td valign="top" align="center">124.5&#x2013;155.3</td>
<td valign="top" align="center">328.9<sup>c</sup>
</td>
<td valign="top" align="center">267.4&#x2013;451</td>
<td valign="top" align="center">72.4</td>
<td valign="top" align="center">3.3 &#xb1; 0.39</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Cymbopogon nardus</italic>
</td>
<td valign="top" align="center">76.5<sup>b</sup>
</td>
<td valign="top" align="center">67.6&#x2013;84.9</td>
<td valign="top" align="center">163<sup>b</sup>
</td>
<td valign="top" align="center">143.9&#x2013;193.5</td>
<td valign="top" align="center">97.5</td>
<td valign="top" align="center">3.9 &#xb1; 0.39</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Ocimum americanum</italic>
</td>
<td valign="top" align="center">89.3<sup>b</sup>
</td>
<td valign="top" align="center">81.1&#x2013;97.4</td>
<td valign="top" align="center">173.0<sup>b</sup>
</td>
<td valign="top" align="center">154.2&#x2013;201.4</td>
<td valign="top" align="center">114.0</td>
<td valign="top" align="center">4.4 &#xb1; 0.41</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Lippia multiflora</italic>
</td>
<td valign="top" align="center">39.5<sup>a</sup>
</td>
<td valign="top" align="center">28.6&#x2013;47.8</td>
<td valign="top" align="center">90.2<sup>a</sup>
</td>
<td valign="top" align="center">78.3&#x2013;108</td>
<td valign="top" align="center">45.1</td>
<td valign="top" align="center">3.2 &#xb1; 0.48</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Eucalyptus camaldulensis</italic>
</td>
<td valign="top" align="center">121.1<sup>c</sup>
</td>
<td valign="top" align="center">109.9&#x2013;133.6</td>
<td valign="top" align="center">267.3<sup>c</sup>
</td>
<td valign="top" align="center">226.6&#x2013;339.4</td>
<td valign="top" align="center">87.7</td>
<td valign="top" align="center">3.7 &#xb1; 0.39</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>LC (lethal concentration) in ppm (part per million). LC values followed by different letters are significantly different.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<p>Regarding LC<sub>50</sub> and LC<sub>90</sub> values, <italic>L. multiflora</italic> exhibited the highest larvicidal activity against the 2 strains of <italic>An. gambiae</italic> (LC<sub>50</sub> = 3.9 ppm, LC<sub>90</sub> = 29.5 ppm for Kisumu larvae and LC<sub>50</sub> = 39.5 ppm and LC<sub>90</sub> = 90.2 ppm for VK larvae).</p>
<p>As for <italic>O. americanum</italic>, it exhibited the weakest larvicidal activity (LC<sub>50</sub> = 75.8 ppm; LC<sub>90</sub> = 193.5 ppm) for Kisumu larvae, while <italic>C. citratus</italic> showed the weakest larvicidal activity (LC<sub>50</sub> = 138.1 ppm; LC<sub>90</sub> = 328.9 ppm) on VK larvae.</p>
<p>Furthermore, oils from <italic>E. camaldulensis</italic>, <italic>C. nardus</italic>, and <italic>C. citratus</italic> still showed strong larvicidal activities after <italic>L. multiflora</italic> with LC<sub>50</sub> values &lt;50 ppm and LC<sub>90</sub> values &lt;91 ppm on Kisumu larvae. On VK larvae, EOs of <italic>C. nardus</italic>, <italic>O. americanum</italic>, and <italic>E. camaldulensis</italic> showed strong larvicidal activities after <italic>L. multiflora</italic> with LC<sub>50</sub> values &lt;140 ppm and LC<sub>90</sub> values &lt;270 ppm.</p>
<p>Only the EO of <italic>L. multiflora</italic> gives LC<sub>50</sub> and LC<sub>90</sub> values close to that of the positive control pyriproxyfen against Kisumu and VK larvae.</p>
<p>Based on the overlap of the CIs of the LC<sub>50</sub> and LC<sub>90</sub> values, no significant difference was observed between <italic>L. multiflora</italic> and pyriproxyfen on the two <italic>An. gambiae</italic> strains tested.</p>
</sec>
<sec id="s3_3">
<title>Larvicidal Activities of Essential Oils Against <italic>Aedes aegypti</italic>
</title>
<p>All EOs from five (5) plant species exhibited toxicity against susceptible strain larvae and 3 and 4 larval instars of <italic>Ae. aegypti</italic> field-collected strain. <xref ref-type="table" rid="T4">
<bold>Tables&#xa0;4</bold>
</xref> and <xref ref-type="table" rid="T5">
<bold>5</bold>
</xref> show the LC<sub>50</sub> and LC<sub>90</sub> values of the EOs of five (5) plants tested against susceptible strains and 3 and 4 larval instars of <italic>Ae. aegypti</italic> field-collected strain.</p>
<table-wrap id="T4" position="float">
<label>Table&#xa0;4</label>
<caption>
<p>Median and 90% lethal concentrations and their Confidence Limits (CLs) of plant essential oils against 3 and 4 larval instars of <italic>Aedes aegypti</italic> susceptible strain from the Bora bora.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Treatment</th>
<th valign="top" align="center">LC<sub>50</sub> (ppm)</th>
<th valign="top" align="center">Confidence limit 95%</th>
<th valign="top" align="center">LC<sub>90</sub> (ppm)</th>
<th valign="top" align="center">Confidence limit 95%</th>
<th valign="top" align="center">X<sup>2</sup>(df)</th>
<th valign="top" align="center">Slope ( &#xb1; SE)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">Pyriproxyfen</td>
<td valign="top" align="center">9.5<sup>a</sup>
</td>
<td valign="top" align="center">6.4&#x2013;12.3</td>
<td valign="top" align="center">43.3<sup>a</sup>
</td>
<td valign="top" align="center">34.0&#x2013;61.8</td>
<td valign="top" align="center">49.7</td>
<td valign="top" align="char" char="&#xb1;">1.9 &#xb1; 0.27</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Cymbopogon citratus</italic>
</td>
<td valign="top" align="center">61.5<sup>c</sup>
</td>
<td valign="top" align="center">51.4&#x2013;70.4</td>
<td valign="top" align="center">132.0<sup>b</sup>
</td>
<td valign="top" align="center">119.4&#x2013;150.1</td>
<td valign="top" align="center">71.9</td>
<td valign="top" align="char" char="&#xb1;">3.2 &#xb1; 0.38</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Cymbopogon nardus</italic>
</td>
<td valign="top" align="center">62.4<sup>c</sup>
</td>
<td valign="top" align="center">50.2&#x2013;72.5</td>
<td valign="top" align="center">108.8<sup>b</sup>
</td>
<td valign="top" align="center">98.4&#x2013;124.0</td>
<td valign="top" align="center">74.2</td>
<td valign="top" align="char" char="&#xb1;">3.09 &#xb1; 0.35</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Ocimum americanum</italic>
</td>
<td valign="top" align="center">91.8<sup>d</sup>
</td>
<td valign="top" align="center">83.3&#x2013;100.3</td>
<td valign="top" align="center">180.9<sup>c</sup>
</td>
<td valign="top" align="center">160.8&#x2013;211.5</td>
<td valign="top" align="center">112.3</td>
<td valign="top" align="char" char="&#xb1;">4.3 &#xb1; 0.41</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Lippia multiflora</italic>
</td>
<td valign="top" align="center">41.9<sup>b</sup>
</td>
<td valign="top" align="center">31.8&#x2013;48.7</td>
<td valign="top" align="center">68.5<sup>a</sup>
</td>
<td valign="top" align="center">61.3&#x2013;84.2</td>
<td valign="top" align="center">39.5</td>
<td valign="top" align="char" char="&#xb1;">2.2 &#xb1; 0.35</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Eucalyptus camaldulensis</italic>
</td>
<td valign="top" align="center">101.3<sup>d</sup>
</td>
<td valign="top" align="center">73.1&#x2013;132.7</td>
<td valign="top" align="center">188.8<sup>c</sup>
</td>
<td valign="top" align="center">169.5&#x2013;217.6</td>
<td valign="top" align="center">120.1</td>
<td valign="top" align="char" char="&#xb1;">1.2 &#xb1; 0.31</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>LC (lethal concentration) in ppm (part per million). LC values followed by different letters are significantly different.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<table-wrap id="T5" position="float">
<label>Table&#xa0;5</label>
<caption>
<p>Median and 90% lethal concentrations and their Confidence Limits (CLs) of plant essential oils against 3 and 4 larval instars of <italic>Aedes aegypti</italic> from Bobo-Dioulasso, field strain.</p>
</caption>
<table frame="hsides">
<thead>
<tr>
<th valign="top" align="left">Treatment</th>
<th valign="top" align="center">LC<sub>50</sub> (ppm)</th>
<th valign="top" align="center">Confidence limit 95%</th>
<th valign="top" align="center">LC<sub>90</sub> (ppm)</th>
<th valign="top" align="center">Confidence limit 95%</th>
<th valign="top" align="center">X<sup>2</sup>(df)</th>
<th valign="top" align="center">Slope ( &#xb1; SE)</th>
</tr>
</thead>
<tbody>
<tr>
<td valign="top" align="left">Pyriproxyfen</td>
<td valign="top" align="center">11.04<sup>a</sup>
</td>
<td valign="top" align="center">8.2&#x2013;13.7</td>
<td valign="top" align="center">43.2<sup>a</sup>
</td>
<td valign="top" align="center">35.3&#x2013;56.1</td>
<td valign="top" align="center">80.8</td>
<td valign="top" align="center">2.1 &#xb1; 0.24</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Cymbopogon citratus</italic>
</td>
<td valign="top" align="center">74.6<sup>c</sup>
</td>
<td valign="top" align="center">67.7&#x2013;81.2</td>
<td valign="top" align="center">152.3<sup>c</sup>
</td>
<td valign="top" align="center">131.9&#x2013;186.0</td>
<td valign="top" align="center">116.2</td>
<td valign="top" align="center">5.1 &#xb1; 0.48</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Cymbopogon nardus</italic>
</td>
<td valign="top" align="center">63.5<sup>c</sup>
</td>
<td valign="top" align="center">57.3&#x2013;69.4</td>
<td valign="top" align="center">148.5<sup>c</sup>
</td>
<td valign="top" align="center">128.4&#x2013;182.6</td>
<td valign="top" align="center">74.2</td>
<td valign="top" align="center">5.4 &#xb1; 0.54</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Ocimum americanum</italic>
</td>
<td valign="top" align="center">79.4<sup>e</sup>
</td>
<td valign="top" align="center">67.6&#x2013;90.2</td>
<td valign="top" align="center">226.3<sup>d</sup>
</td>
<td valign="top" align="center">186.9&#x2013;302.9</td>
<td valign="top" align="center">64.4</td>
<td valign="top" align="center">2.8 &#xb1; 0.35</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Lippia multiflora</italic>
</td>
<td valign="top" align="center">42<sup>b</sup>
</td>
<td valign="top" align="center">33.4&#x2013;47.3</td>
<td valign="top" align="center">74.6<sup>b</sup>
</td>
<td valign="top" align="center">65.3&#x2013;92.5</td>
<td valign="top" align="center">22.0</td>
<td valign="top" align="center">6.0 &#xb1; 1.28</td>
</tr>
<tr>
<td valign="top" align="left">
<italic>Eucalyptus camaldulensis</italic>
</td>
<td valign="top" align="center">103.8<sup>d</sup>
</td>
<td valign="top" align="center">95.4&#x2013;112.3</td>
<td valign="top" align="center">311.3<sup>d</sup>
</td>
<td valign="top" align="center">238&#x2013;503.1</td>
<td valign="top" align="center">18.3</td>
<td valign="top" align="center">4.9 &#xb1; 0.45</td>
</tr>
</tbody>
</table>
<table-wrap-foot>
<fn>
<p>LC (lethal concentration) in ppm (part per million). LC values followed by different letters are significantly different.</p>
</fn>
</table-wrap-foot>
</table-wrap>
<p>As in the case of <italic>An. gambiae</italic> populations, among the EOs tested, <italic>L. multiflora</italic> was the most toxic EO on the two (2) strains of <italic>Ae. aegypti</italic> tested. Indeed, LC<sub>50</sub> and LC<sub>90</sub> values were 42 and 74.6 ppm, respectively, for <italic>L. multiflora</italic> tested on the susceptible strain of <italic>Ae. aegypti</italic> (Bora bora) and 3 and 4 larval instars of <italic>Ae. aegypti</italic> field-collected strain from Bobo-Dioulasso and lower for those from other EOs tested where the LC<sub>50</sub> and LC<sub>90</sub> values ranged from 61.5 to 103.8 ppm and 108.8 to 311.3 ppm, respectively.</p>
<p>For the Bora bora strain, LC<sub>50</sub> and LC<sub>90</sub> values were 61.5, 62.4, 91.8, 41.9, and 101.3 ppm and 132, 108.8, 180.9, 68.5, and 188.8 ppm for EOs from <italic>C. citratus</italic>, <italic>C. nardus</italic>, <italic>E. camaldulensis</italic>, <italic>L. multiflora</italic>, and <italic>O. americanum</italic>, respectively (<xref ref-type="table" rid="T4">
<bold>Table&#xa0;4</bold>
</xref>). These values were close to those obtained with the field strain collected from Bobo-Dioulasso (LC<sub>50</sub> and LC<sub>90</sub> values were 74.6, 63.5, 79.4, 41.9, and 103.8 ppm and 152.3, 148.5, 226.3, 74.6, and 1,053.6 ppm with EOs from <italic>C. citratus</italic>, <italic>C. nardus</italic>, <italic>E. camaldulensis</italic>, <italic>L. multiflora</italic>, and <italic>O. americanum</italic>, respectively) (<xref ref-type="table" rid="T5">
<bold>Table&#xa0;5</bold>
</xref>). EO of <italic>E. camaldulensis</italic> remains the least toxic to both strains of <italic>Ae. aegypti</italic> regarding the LC<sub>50</sub> and LC<sub>90</sub> values above 100 and 188 ppm, respectively.</p>
<p>Based on the overlap of the CIs of the LC<sub>50</sub> and LC<sub>90</sub> values, there were no significant differences between <italic>L. multiflora</italic> and pyriproxyfen at LC<sub>90</sub> with Bora bora. Also, there were no significant differences between <italic>C. citratus</italic> and <italic>C. nardus</italic> regarding LC<sub>50</sub> and LC<sub>90</sub> values with the two <italic>Ae. aegypti</italic> strains tested. Also, there were no significant differences between <italic>E. camaldulensis</italic> and <italic>O. americanum</italic> regarding LC<sub>90</sub> with the two <italic>Ae. aegypti</italic> strains tested and LC<sub>50</sub> with Bora bora. It is also the same with <italic>C. citratus</italic> and <italic>C. nardus</italic>, in regard to LC<sub>50</sub> and LC<sub>90</sub> values found in two <italic>Ae. aegypti</italic> strains tested.</p>
</sec>
</sec>
<sec id="s4" sec-type="discussion">
<title>Discussion</title>
<p>Up to now, long-lasting insecticidal nets (LLIN) and indoor residual spraying (IRS) remain the two main tools targeting mainly adults <italic>An. gambiae</italic> and to lesser extent <italic>Ae. aegypti</italic> vectors. Thus, there is an urgent need to develop innovative tools and techniques including EOs used against eggs, larvae instar, and adults in order to increase the success of vector control (<xref ref-type="bibr" rid="B11">11</xref>).</p>
<p>Our study aimed at evaluating the bioefficacy of five EOs on <italic>Ae. aegypti</italic> and <italic>An. gambiae</italic> larvae according to the WHO standard methods. Most studies have already performed the larvicidal tests but did not include the chemical control pyriproxyfen, an insect growth regulator (IGR). IGR acts by mimicking one of these hormones or directly perturbating cuticle formation/deposition or lipid biosynthesis.</p>
<p>In this current study, all EOs tested exhibited variable insecticide activity against the larvae of <italic>An. gambiae</italic> and <italic>Ae. aegypti</italic>. Regarding LC<sub>50</sub> and LC<sub>90</sub> values, the EOs from <italic>C. citratus</italic>, <italic>C. nardus</italic>, <italic>E. camaldulensis</italic>, <italic>L. multiflora</italic>, and <italic>O. americanum</italic> exhibited higher larvicidal activities against third and fourth instar laboratory-reared larvae of <italic>An. gambiae</italic> and <italic>Ae. aegypti</italic> after 24&#xa0;h of exposure, the most toxic of all being that of <italic>L. multiflora</italic>. LC<sub>50</sub> of EO from <italic>E. camaldulensis</italic> was the least toxic against <italic>Ae. aegypti</italic>, whereas <italic>C. citratus</italic> remains the least toxic against <italic>An. gambiae</italic>. These data are not in agreement with those found by Manh et&#xa0;al. (<xref ref-type="bibr" rid="B27">27</xref>), who reported that on <italic>Ae. aegypti</italic> larvae, <italic>C. citratus</italic> EO (LC<sub>50</sub> = 120.6 ppm) was less effective than that of <italic>E. camaldulensis</italic> (LC<sub>50</sub> = 33.7 ppm).</p>
<p>Our results obtained with <italic>C. nardus</italic> on <italic>An. gambiae</italic> in this study were below those obtained by Ahouansou et&#xa0;al. (<xref ref-type="bibr" rid="B19">19</xref>), who obtained a value of 97.3 ppm for LC<sub>50</sub> on <italic>An. gambiae</italic>. Our results were similar to those reported by Solon et&#xa0;al. (<xref ref-type="bibr" rid="B28">28</xref>) on <italic>Ae. aegypti</italic> populations. In their study, <italic>O. americanum</italic> and <italic>C. citratus</italic> exhibited values of LC<sub>50</sub> equaling 67 and 69 ppm, respectively. However, the results with <italic>O. americanum</italic> were below those reported by Wangrawa et&#xa0;al. (<xref ref-type="bibr" rid="B21">21</xref>) on <italic>An. gambiae</italic> whose LC<sub>50</sub> was 209.84 ppm.</p>
<p>The LC<sub>50</sub> and LC<sub>90</sub> values obtained with the <italic>L. multiflora</italic> in this current study were lowest than those reported by Bassole et&#xa0;al. (<xref ref-type="bibr" rid="B23">23</xref>). Recently, the same trend was observed by Yameogo et&#xa0;al. (<xref ref-type="bibr" rid="B22">22</xref>), who showed also the toxic effect of <italic>L. multiflora</italic> against <italic>Ae. aegypti</italic> populations from Tabtenga, Ouagadougou.</p>
<p>Interestingly, the high toxicity of the <italic>L. multiflora</italic> EO could result in the presence of three major components: thymol, <italic>p</italic>-cymene, and &#x3b2;-caryophyllene. According to Folashade (<xref ref-type="bibr" rid="B29">29</xref>), thymol, germacrene D, <italic>p</italic>-cymene, thymyl acetate, and sabinene were found in EOs of <italic>L. multiflora</italic> in Ghana and seem to be involved in <italic>Lippia</italic> toxicity. Conversely, the lower larvicidal activities of <italic>C. citratus</italic>, <italic>C. nardus</italic>, <italic>E. camaldulensis</italic>, and <italic>O. americanum</italic> oils could be explained by the minor effect of piperitone, geraniol, and 1.8-cineole against <italic>Ae. aegypti</italic> and <italic>An. gambiae</italic> larvae. This could explain the differences observed in biological activity among the EOs.</p>
<p>Regarding the LC<sub>50</sub> and LC<sub>90</sub> values, the bioefficacy of <italic>L. multiflora</italic> on <italic>An. gambiae</italic> strains is closer to that of the positive control used in this study, which is pyriproxyfen, the reference larvicide used against larvae. This would open new alternatives for mosquito control.</p>
<p>Globally, in <italic>An. gambiae</italic> strain populations, the laboratory-reared larvae were found to be the most susceptible to EOs than those from the field population (VK), known for their resistance to pyrethroid (<xref ref-type="bibr" rid="B30">30</xref>&#x2013;<xref ref-type="bibr" rid="B32">32</xref>).</p>
<p>As observed in <italic>An. gambiae</italic> populations, <italic>Ae. aegypti</italic> larvae were the most susceptible to <italic>L. multiflora</italic> after the chemical pyriproxyfen. The LC<sub>50</sub> values found in this study were slightly lower than those observed in <italic>Ae. aegypti</italic> populations from Ouagadougou (<xref ref-type="bibr" rid="B22">22</xref>), explaining the occurrence of the phenotypic resistance to the main chemical.</p>
<p>As shown by Namountougou et&#xa0;al. (<xref ref-type="bibr" rid="B33">33</xref>), tests performed with deltamethrin on <italic>Ae. aegypti</italic> populations collected from Bobo-Dioulasso showed mortality rates reaching 89.62% and 82.72% for 2013 and 2014, respectively. Mortality rates of <italic>Ae. aegypti</italic> collected from Ouagadougou were 50.7% and 20.7% for 2013 and 2014, respectively. All these values were lower than 90%, suggesting a resistance. It is very urgent to search for an alternative to chemicals. Our data will help to develop innovative strategies based on EOs.</p>
</sec>
<sec id="s5">
<title>Conclusion</title>
<p>Our results showed that the use of EOs as larvicides is a promising strategy. Therefore, they could be the object of particular attention in the search for new natural, selective, and biodegradable larvicidal products that can be used in public health vector control programs against <italic>An. gambiae</italic> and <italic>Ae. aegypti</italic> in particular.</p>
</sec>
<sec id="s6" sec-type="data-availability">
<title>Data Availability Statement</title>
<p>The original contributions presented in the study are included in the article/supplementary materials, further inquiries can be directed to the corresponding author/s.</p>
</sec>
<sec id="s7" sec-type="author-contributions">
<title>Author Contributions</title>
<p>MB and OG designed the study. DS critically supervised the study. MB, HK, GM, and OT carried out the laboratory experiments. MB, SD, and OG analyzed and interpreted the data and drafted the manuscript. OG, RD, and MN revised the manuscript. All authors contributed to the article and approved the submitted version.</p>
</sec>
<sec id="s8" sec-type="funding-information">
<title>Funding</title>
<p>Funding for this study was provided partly by the TWAS 18-163 RG/BIO/AF/AC_G-FR3240303649 and the Centre d&#x2019;excellence Africain (CEA) en Innovations biotechnologiques pour l&#x2019;elimination des maladies a transmission vectorielle. I also thanks LAMIVECT (Laboratoire Mixte International sur les Maladies &#xe0; transmissions Vectorielle) for supporting publication fees.</p>
</sec>
<sec id="s9" sec-type="COI-statement">
<title>Conflict of Interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec id="s10" sec-type="disclaimer">
<title>Publisher&#x2019;s Note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
</body>
<back>
<ack>
<title>Acknowledgments</title>
<p>We are indebted to &#x201c;Institut de recherche en Sciences Appliqu&#xe9;es et technologiques&#x201d; (IRSAT) for providing us with essential oils.</p>
</ack>
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