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Myers A, Fagbohoun J, Houetohossou G, Ndombidje B, Govoetchan R, Todjinou D, Ngufor C. Identifying suitable methods for evaluating the sterilizing effects of pyriproxyfen on adult malaria vectors: a comparison of the oviposition and ovary dissection methods. Malar J 2024; 23:164. [PMID: 38789998 PMCID: PMC11127354 DOI: 10.1186/s12936-024-04983-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2023] [Accepted: 05/14/2024] [Indexed: 05/26/2024] Open
Abstract
BACKGROUND Nets containing pyriproxyfen, an insect growth regulator that sterilizes adult mosquitoes, have become available for malaria control. Suitable methods for investigating vector susceptibility to pyriproxyfen and evaluating its efficacy on nets need to be identified. The sterilizing effects of pyriproxyfen on adult malaria vectors can be assessed by measuring oviposition or by dissecting mosquito ovaries to determine damage by pyriproxyfen (ovary dissection). METHOD Laboratory bioassays were performed to compare the oviposition and ovary dissection methods for monitoring susceptibility to pyriproxyfen in wild malaria vectors using WHO bottle bioassays and for evaluating its efficacy on nets in cone bioassays. Blood-fed mosquitoes of susceptible and pyrethroid-resistant strains of Anopheles gambiae sensu lato were exposed to pyriproxyfen-treated bottles (100 μg and 200 μg) and to unwashed and washed pieces of a pyriproxyfen long-lasting net in cone bioassays. Survivors were assessed for the sterilizing effects of pyriproxyfen using both methods. The methods were compared in terms of their reliability, sensitivity, specificity, resources (cost and time) required and perceived difficulties by trained laboratory technicians. RESULTS The total number of An. gambiae s.l. mosquitoes assessed for the sterilizing effects of pyriproxyfen were 1745 for the oviposition method and 1698 for the ovary dissection method. Fertility rates of control unexposed mosquitoes were significantly higher with ovary dissection compared to oviposition in both bottle bioassays (99-100% vs. 34-59%, P < 0.05) and cone bioassays (99-100% vs. 18-33%, P < 0.001). Oviposition rates of control unexposed mosquitoes were lower with wild pyrethroid-resistant An. gambiae s.l. Cové, compared to the laboratory-maintained reference susceptible An gambiae sensu stricto Kisumu (18-34% vs. 58-76%, P < 0.05). Sterilization rates of the Kisumu strain in bottle bioassays with the pyriproxyfen diagnostic dose (100 μg) were suboptimal with the oviposition method (90%) but showed full susceptibility with ovary dissection (99%). Wild pyrethroid-resistant Cové mosquitoes were fully susceptible to pyriproxyfen in bottle bioassays using ovary dissection (> 99%), but not with the oviposition method (69%). Both methods showed similar levels of sensitivity (89-98% vs. 89-100%). Specificity was substantially higher with ovary dissection compared to the oviposition method in both bottle bioassays (99-100% vs. 34-48%) and cone tests (100% vs.18-76%). Ovary dissection was also more sensitive for detecting the residual activity of pyriproxyfen in a washed net compared to oviposition. The oviposition method though cheaper, was less reliable and more time-consuming. Laboratory technicians preferred ovary dissection mostly due to its reliability. CONCLUSION The ovary dissection method was more accurate, more reliable and more efficient compared to the oviposition method for evaluating the sterilizing effects of pyriproxyfen on adult malaria vectors in susceptibility bioassays and for evaluating the efficacy of pyriproxyfen-treated nets.
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Affiliation(s)
- Alesha Myers
- London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT, UK
| | - Josias Fagbohoun
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin
| | | | - Boris Ndombidje
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin
| | - Renaud Govoetchan
- London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT, UK
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin
- African Institute for Research in Infectious Diseases (AIRID), Cotonou, Benin
| | - Damien Todjinou
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin
| | - Corine Ngufor
- London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT, UK.
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin.
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin.
- African Institute for Research in Infectious Diseases (AIRID), Cotonou, Benin.
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Hancock PA, Ochomo E, Messenger LA. Genetic surveillance of insecticide resistance in African Anopheles populations to inform malaria vector control. Trends Parasitol 2024:S1471-4922(24)00115-6. [PMID: 38760258 DOI: 10.1016/j.pt.2024.04.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2024] [Revised: 04/24/2024] [Accepted: 04/26/2024] [Indexed: 05/19/2024]
Abstract
Insecticide resistance in malaria vector populations poses a major threat to malaria control, which relies largely on insecticidal interventions. Contemporary vector-control strategies focus on combatting resistance using multiple insecticides with differing modes of action within the mosquito. However, diverse genetic resistance mechanisms are present in vector populations, and continue to evolve. Knowledge of the spatial distribution of these genetic mechanisms, and how they impact the efficacy of different insecticidal products, is critical to inform intervention deployment decisions. We developed a catalogue of genetic-resistance mechanisms in African malaria vectors that could guide molecular surveillance. We highlight situations where intervention deployment has led to resistance evolution and spread, and identify challenges in understanding and mitigating the epidemiological impacts of resistance.
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Affiliation(s)
- Penelope A Hancock
- Department of Infectious Disease Epidemiology, Imperial College London, London, UK.
| | - Eric Ochomo
- Centre for Global Health Research, Kenya Medical Research Institute, Kisumu, Kenya; Vector Group, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, UK
| | - Louisa A Messenger
- Department of Environmental and Occupational Health, School of Public Health, University of Nevada, Las Vegas, USA; Parasitology and Vector Biology (PARAVEC) Laboratory, School of Public Health, University of Nevada, Las Vegas, USA
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Ashu FA, Fouet C, Ambadiang MM, Penlap-Beng V, Kamdem C. Adult mosquitoes of the sibling species Anopheles gambiae and Anopheles coluzzii exhibit contrasting patterns of susceptibility to four neonicotinoid insecticides along an urban-to-rural gradient in Yaoundé, Cameroon. Malar J 2024; 23:65. [PMID: 38431623 PMCID: PMC10909279 DOI: 10.1186/s12936-024-04876-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2023] [Accepted: 02/10/2024] [Indexed: 03/05/2024] Open
Abstract
BACKGROUND Neonicotinoids are potential alternatives for controlling pyrethroid-resistant mosquitoes, but their efficacy against malaria vector populations of sub-Saharan Africa has yet to be investigated. The aim of the present study was to test the efficacy of four neonicotinoids against adult populations of the sibling species Anopheles gambiae and Anopheles coluzzii sampled along an urban-to-rural gradient. METHODS The lethal toxicity of three active ingredients for adults of two susceptible Anopheles strains was assessed using concentration-response assays, and their discriminating concentrations were calculated. The discriminating concentrations were then used to test the susceptibility of An. gambiae and An. coluzzii mosquitoes collected from urban, suburban and rural areas of Yaoundé, Cameroon, to acetamiprid, imidacloprid, clothianidin and thiamethoxam. RESULTS Lethal concentrations of neonicotinoids were relatively high suggesting that this class of insecticides has low toxicity against Anopheles mosquitoes. Reduced susceptibility to the four neonicotinoids tested was detected in An. gambiae populations collected from rural and suburban areas. By contrast, adults of An. coluzzii that occurred in urbanized settings were susceptible to neonicotinoids except acetamiprid for which 80% mortality was obtained within 72 h of insecticide exposure. The cytochrome inhibitor, piperonyl butoxide (PBO), significantly enhanced the activity of clothianidin and acetamiprid against An. gambiae mosquitoes. CONCLUSIONS These findings corroborate susceptibility profiles observed in larvae and highlight a significant variation in tolerance to neonicotinoids between An. gambiae and An. coluzzii populations from Yaoundé. Further studies are needed to disentangle the role of exposure to agricultural pesticides and of cross-resistance mechanisms in the development of neonicotinoid resistance in some Anopheles species.
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Affiliation(s)
- Fred A Ashu
- Centre for Research in Infectious Diseases, P.O. Box 13591, Yaoundé 9, Cameroon
- Department of Biochemistry, Faculty of Science, University of Yaoundé 1, P.O. Box 11 812, Yaoundé, Cameroon
| | - Caroline Fouet
- Department of Biological Sciences, The University of Texas at El Paso, 500 W. University Ave., El Paso, TX, 79968, USA
| | - Marilene M Ambadiang
- Centre for Research in Infectious Diseases, P.O. Box 13591, Yaoundé 9, Cameroon
- Department of Biochemistry, Faculty of Science, University of Yaoundé 1, P.O. Box 11 812, Yaoundé, Cameroon
| | - Véronique Penlap-Beng
- Department of Biochemistry, Faculty of Science, University of Yaoundé 1, P.O. Box 11 812, Yaoundé, Cameroon
| | - Colince Kamdem
- Department of Biological Sciences, The University of Texas at El Paso, 500 W. University Ave., El Paso, TX, 79968, USA.
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Ambadiang M, Fouet C, Ashu F, Bouaka C, Penlap-Beng V, Kamdem C. Anopheles gambiae larvae's ability to grow and emerge in water containing lethal concentrations of clothianidin, acetamiprid, or imidacloprid is consistent with cross-resistance to neonicotinoids. Parasit Vectors 2024; 17:98. [PMID: 38429846 PMCID: PMC10905935 DOI: 10.1186/s13071-024-06188-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Accepted: 02/08/2024] [Indexed: 03/03/2024] Open
Abstract
BACKGROUND For decades, various agrochemicals have been successfully repurposed for mosquito control. However, preexisting resistance caused in larval and adult populations by unintentional pesticide exposure or other cross-resistance mechanisms poses a challenge to the efficacy of this strategy. A better understanding of larval adaptation to the lethal and sublethal effects of residual pesticides in aquatic habitats would provide vital information for assessing the efficacy of repurposed agrochemicals against mosquitoes. METHODS We reared field-collected mosquito larvae in water containing a concentration of agrochemical causing 100% mortality in susceptible mosquitoes after 24 h (lethal concentration). Using this experimental setup, we tested the effect of lethal concentrations of a pyrrole (chlorfenapyr, 0.10 mg/l), a pyrethroid (deltamethrin, 1.5 mg/l), and three neonicotinoids including imidacloprid (0.075 mg/l), acetamiprid (0.15 mg/l), and clothianidin (0.035 mg/l) on mortality rates, growth, and survival in third-instar larvae of the two sibling species Anopheles gambiae and Anopheles coluzzii collected from Yaoundé, Cameroon. RESULTS We found that An. gambiae and An. coluzzii larvae were susceptible to chlorfenapyr and were killed within 24 h by a nominal concentration of 0.10 mg/l. Consistent with strong resistance, deltamethrin induced low mortality in both species. Lethal concentrations of acetamiprid, imidacloprid, and clothianidin strongly inhibited survival, growth, and emergence in An. coluzzii larvae. By contrast, depending on the active ingredient and the population tested, 5-60% of immature stages of An. gambiae were able to grow and emerge in water containing a lethal concentration of neonicotinoids, suggesting cross-resistance to this class of insecticides. CONCLUSIONS These findings corroborate susceptibility profiles observed in adults and suggest that unintentional pesticide exposure or other cross-resistance processes could contribute to the development of resistance to neonicotinoids in some Anopheles populations.
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Affiliation(s)
- Marilene Ambadiang
- Centre for Research in Infectious Diseases (CRID), Yaoundé, Cameroon
- Department of Biochemistry, Faculty of Science, University of Yaoundé 1, Yaoundé, Cameroon
| | - Caroline Fouet
- Department of Biological Sciences, The University of Texas at El Paso, El Paso, TX, USA
| | - Fred Ashu
- Centre for Research in Infectious Diseases (CRID), Yaoundé, Cameroon
- Department of Biochemistry, Faculty of Science, University of Yaoundé 1, Yaoundé, Cameroon
| | - Calmes Bouaka
- Centre for Research in Infectious Diseases (CRID), Yaoundé, Cameroon
- Department of Biochemistry, Faculty of Science, University of Yaoundé 1, Yaoundé, Cameroon
| | - Véronique Penlap-Beng
- Department of Biochemistry, Faculty of Science, University of Yaoundé 1, Yaoundé, Cameroon
| | - Colince Kamdem
- Department of Biological Sciences, The University of Texas at El Paso, El Paso, TX, USA.
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Alarcón-Elbal PM, Suárez-Balseiro C, De Souza C, Soriano-López A, Riggio-Olivares G. History of research on Aedes albopictus (Diptera: Culicidae) in Europe: approaching the world's most invasive mosquito species from a bibliometric perspective. Parasitol Res 2024; 123:130. [PMID: 38340244 DOI: 10.1007/s00436-024-08137-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 01/19/2024] [Indexed: 02/12/2024]
Abstract
The Asian tiger mosquito, Aedes albopictus (Skuse), is an invasive species native to Southeast Asia. This insect, which is an important vector of arbovirus such as dengue, Zika, and chikungunya, has spread rapidly to several parts of the world over the last few decades. This study employed a bibliometric approach to explore, for the first time, Ae. albopictus research activity and output in Europe. We used the Web of Science Core Collection data source to characterize the current scientific research. A total of 903 publications from 1973 to 2022 were retrieved. We also provided a comprehensive analysis by year of publication; distribution by most productive European countries, institutions, and authors; collaboration networks; research topics; most productive journals; and most cited publications. Results showed a notable increase in the number of studies after the chikungunya virus outbreak in Northeast Italy in 2007. More than 60% of these publications across the entire European continent originated from France and Italy. Research output related to 'population and community ecology' topics was significantly high. The most common type of collaboration was national, which occurred between institutions in the same European country. By providing an overview of Ae. albopictus research in Europe, this work contributes to upcoming debates, decision-making, planning on research and development, and public health strategies on the continent and worldwide.
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Affiliation(s)
- Pedro María Alarcón-Elbal
- Department of Animal Production and Health, Facultad de Veterinaria, Veterinary Public Health and Food Science and Technology (PASAPTA), Universidad Cardenal Herrera-CEU, CEU Universities, Valencia, Spain.
| | - Carlos Suárez-Balseiro
- College of Communication and Information, University of Puerto Rico, Río Piedras Campus, San Juan, Puerto Rico.
| | - Cláudia De Souza
- College of Communication and Information, University of Puerto Rico, Río Piedras Campus, San Juan, Puerto Rico
| | - Ashley Soriano-López
- School of Medicine, Universidad Iberoamericana (UNIBE), Santo Domingo, Dominican Republic
| | - Giovanna Riggio-Olivares
- Learning and Research Resources Centre, Universidad Iberoamericana (UNIBE), Santo Domingo, Dominican Republic
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Fouet C, Ashu FA, Ambadiang MM, Tchapga W, Wondji CS, Kamdem C. Clothianidin-resistant Anopheles gambiae adult mosquitoes from Yaoundé, Cameroon, display reduced susceptibility to SumiShield® 50WG, a neonicotinoid formulation for indoor residual spraying. BMC Infect Dis 2024; 24:133. [PMID: 38273227 PMCID: PMC10811947 DOI: 10.1186/s12879-024-09030-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Accepted: 01/18/2024] [Indexed: 01/27/2024] Open
Abstract
BACKGROUND Chronic exposure of mosquito larvae to pesticide residues and cross-resistance mechanisms are major drivers of tolerance to insecticides used for vector control. This presents a concern for the efficacy of clothianidin, an agricultural neonicotinoid prequalified for Indoor Residual Spraying (IRS). METHODS Using standard bioassays, we tested if reduced susceptibility to clothianidin can affect the efficacy of SumiShield® 50WG, one of four new IRS formulations containing clothianidin. We simultaneously monitored susceptibility to clothianidin and to SumiShield 50WG, testing adults of Anopheles gambiae, An. coluzzii and Culex sp sampled from urban, suburban and agricultural areas of Yaoundé, Cameroon. RESULTS We found that in this geographic area, the level of susceptibility to the active ingredient predicted the efficacy of SumiShield 50WG. This formulation was very potent against populations that reached 100% mortality within 72 h of exposure to a discriminating concentration of clothianidin. By contrast, mortality leveled off at 75.4 ± 3.5% within 7 days of exposure to SumiShield 50WG in An. gambiae adults collected from a farm where the spraying of the two neonicotinoids acetamiprid and imidacloprid for crop protection is likely driving resistance to clothianidin. CONCLUSIONS Despite the relatively small geographic extend of the study, the findings suggest that cross-resistance may impact the efficacy of some new IRS formulations and that alternative compounds could be prioritized in areas where neonicotinoid resistance is emerging.
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Affiliation(s)
- Caroline Fouet
- Department of Biological Sciences, The University of Texas at El Paso, 500 W. University Ave, El Paso, TX, 79968, USA
| | - Fred A Ashu
- Centre for Research in Infectious Diseases (CRID), P.O. Box 13591, Yaoundé, Cameroon
- Department of Biochemistry, Faculty of Science, University of Yaoundé 1, P.O. Box 812, Yaoundé, Cameroon
| | - Marilene M Ambadiang
- Centre for Research in Infectious Diseases (CRID), P.O. Box 13591, Yaoundé, Cameroon
- Department of Biochemistry, Faculty of Science, University of Yaoundé 1, P.O. Box 812, Yaoundé, Cameroon
| | - Williams Tchapga
- Centre for Research in Infectious Diseases (CRID), P.O. Box 13591, Yaoundé, Cameroon
| | - Charles S Wondji
- Centre for Research in Infectious Diseases (CRID), P.O. Box 13591, Yaoundé, Cameroon
- Vector Biology Department, Liverpool School of Tropical Medicine (LSTM), Pembroke Place, Liverpool, L3 5QA, UK
| | - Colince Kamdem
- Department of Biological Sciences, The University of Texas at El Paso, 500 W. University Ave, El Paso, TX, 79968, USA.
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Pai HH, Chang CY, Lin KC, Hsu EL. Rapid insecticide resistance bioassays for three major urban insects in Taiwan. Parasit Vectors 2023; 16:447. [PMID: 38042818 PMCID: PMC10693703 DOI: 10.1186/s13071-023-06055-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Accepted: 11/13/2023] [Indexed: 12/04/2023] Open
Abstract
BACKGROUND Taiwan's warm and humid climate and dense population provide a suitable environment for the breeding of pests. The three major urban insects in Taiwan are house flies, cockroaches, and mosquitoes. In cases where a disease outbreak or high pest density necessitates chemical control, selecting the most effective insecticide is crucial. The resistance of pests to the selected environmental insecticide must be rapidly assessed to achieve effective chemical control and reduce environmental pollution. METHODS In this study, we evaluated the resistance of various pests, namely, house flies (Musca domestica L.), cockroaches (Blattella germanica L. and Periplaneta americana), and mosquitoes (Aedes aegypti and Ae. albopictus) against 10 commonly used insecticides. Rapid insecticide resistance bioassays were performed using discriminating doses or concentrations of the active ingredients of insecticides. RESULTS Five field strains of M. domestica (L.) are resistant to all 10 commonly used insecticides and exhibit cross- and multiple resistance to four types of pyrethroids and three types of organophosphates, propoxur, fipronil, and imidacloprid. None of the five field strains of P. americana are resistant to any of the tested insecticides, and only one strain of B. germanica (L.) is resistant to permethrin. One strain of Ae. albopictus is resistant to pirimiphos-methyl, whereas five strains of Ae. aegypti exhibit multiple resistance to pyrethroids, organophosphates, and other insecticides. CONCLUSIONS In the event of a disease outbreak or high pest density, rapid insecticide resistance bioassays may be performed using discriminating doses or concentrations to achieve precise and effective chemical control, reduce environmental pollution, and increase control efficacy.
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Affiliation(s)
- Hsiu-Hua Pai
- Department of Kinesiology, Health, and Leisure Studies, National University of Kaohsiung, Kaohsiung, Taiwan (ROC).
| | - Chun-Yung Chang
- Department of Kinesiology, Health, and Leisure Studies, National University of Kaohsiung, Kaohsiung, Taiwan (ROC)
| | - Kai-Chen Lin
- Department of Kinesiology, Health, and Leisure Studies, National University of Kaohsiung, Kaohsiung, Taiwan (ROC)
| | - Err-Lieh Hsu
- Department of Entomology, National Taiwan University, Taipei, Taiwan (ROC)
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Ashu FA, Fouet C, Ambadiang MM, Penlap-Beng V, Kamdem C. Vegetable oil-based surfactants are adjuvants that enhance the efficacy of neonicotinoid insecticides and can bias susceptibility testing in adult mosquitoes. PLoS Negl Trop Dis 2023; 17:e0011737. [PMID: 37976311 PMCID: PMC10656025 DOI: 10.1371/journal.pntd.0011737] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Accepted: 10/18/2023] [Indexed: 11/19/2023] Open
Abstract
BACKGROUND The standard operating procedure for testing the susceptibility of adult mosquitoes to neonicotinoid or butenolide insecticides recommends using a vegetable oil ester (Mero) as a surfactant. However, there is growing evidence that this adjuvant contains surfactants that can enhance insecticide activity, mask resistance and bias the bioassay. METHODOLOGY/PRINCIPAL FINDINGS Using standard bioassays, we tested the effects of commercial formulations of vegetable oil-based surfactants similar to Mero on the activity of a spectrum of active ingredients including four neonicotinoids (acetamiprid, clothianidin, imidacloprid and thiamethoxam) and two pyrethroids (permethrin and deltamethrin). We found that three different brands of linseed oil soap used as cleaning products drastically enhanced neonicotinoid activity in Anopheles mosquitoes. At 1% (v/v), the surfactant reduced the median lethal concentration, LC50, of clothianidin more than 10-fold both in susceptible and in resistant populations of Anopheles gambiae. At 1% or 0.5% (v/v), linseed oil soap restored the susceptibility of adult mosquitoes fully to clothianidin, thiamethoxam and imidacloprid and partially to acetamiprid. By contrast, adding soap to the active ingredient did not significantly affect the level of resistance to permethrin or deltamethrin suggesting that vegetable oil-based surfactants specifically enhance the potency of some classes of insecticides. CONCLUSIONS/SIGNIFICANCE Our findings indicate that surfactants are not inert ingredients, and their use in susceptibility testing may jeopardize the ability to detect resistance. Further research is needed to evaluate the potential, the limitations and the challenges of using some surfactants as adjuvants to enhance the potency of some chemicals applied in mosquito control.
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Affiliation(s)
- Fred A. Ashu
- Centre for Research in Infectious Diseases (CRID), Yaoundé, Cameroon
- Department of Biochemistry, Faculty of Science, University of Yaoundé, Yaoundé, Cameroon
| | - Caroline Fouet
- Department of Biological Sciences, The University of Texas at El Paso, El Paso, Texas, United States of America
| | - Marilene M. Ambadiang
- Centre for Research in Infectious Diseases (CRID), Yaoundé, Cameroon
- Department of Biochemistry, Faculty of Science, University of Yaoundé, Yaoundé, Cameroon
| | - Véronique Penlap-Beng
- Department of Biochemistry, Faculty of Science, University of Yaoundé, Yaoundé, Cameroon
| | - Colince Kamdem
- Department of Biological Sciences, The University of Texas at El Paso, El Paso, Texas, United States of America
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Ngufor C, Fongnikin A, Fagbohoun J, Agbevo A, Syme T, Ahoga J, Accrombessi M, Protopopoff N, Cook J, Churcher TS, Padonou GG, Govoetchan R, Akogbeto M. Evaluating the attrition, fabric integrity and insecticidal durability of two dual active ingredient nets (Interceptor ® G2 and Royal ® Guard): methodology for a prospective study embedded in a cluster randomized controlled trial in Benin. Malar J 2023; 22:276. [PMID: 37716970 PMCID: PMC10504698 DOI: 10.1186/s12936-023-04708-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 09/07/2023] [Indexed: 09/18/2023] Open
Abstract
BACKGROUND Following the World Health Organization (WHO) endorsement of dual active ingredient (AI) nets, an increased uptake of pyrethroid-chlorfenapyr and pyrethroid-pyriproxyfen nets is expected. Studies evaluating their physical and insecticidal durability are essential for making programmatic and procurement decisions. This paper describes the methodology for a prospective study to evaluate the attrition, fabric integrity, insecticidal durability of Interceptor® G2 (alpha-cypermethrin-chlorfenapyr) and Royal Guard® (alpha-cypermethrin-pyriproxyfen), compared to Interceptor® (alpha-cypermethrin), embedded in a 3-arm cluster randomized controlled trial (cRCT) in the Zou Department of Benin. METHODS Ten clusters randomly selected from each arm of the cRCT will be used for the study. A total of 750 ITNs per type will be followed in 5 study clusters per arm to assess ITN attrition and fabric integrity at 6-, 12-, 24- and 36-months post distribution, using standard WHO procedures. A second cohort of 1800 nets per type will be withdrawn every 6 months from all 10 clusters per arm and assessed for chemical content and biological activity in laboratory bioassays at each time point. Alpha-cypermethrin bioefficacy in Interceptor® and Royal Guard® will be monitored in WHO cone bioassays and tunnel tests using the susceptible Anopheles gambiae Kisumu strain. The bioefficacy of the non-pyrethroid insecticides (chlorfenapyr in Interceptor® G2 and pyriproxyfen in Royal Guard®) will be monitored using the pyrethroid-resistant Anopheles coluzzii Akron strain. Chlorfenapyr activity will be assessed in tunnel tests while pyriproxyfen activity will be assessed in cone bioassays in terms of the reduction in fertility of blood-fed survivors observed by dissecting mosquito ovaries. Nets withdrawn at 12, 24 and 36 months will be tested in experimental hut trials within the cRCT study area against wild free-flying pyrethroid resistant An. gambiae sensu lato to investigate their superiority to Interceptor® and to compare them to ITNs washed 20 times for experimental hut evaluation studies. Mechanistic models will also be used to investigate whether entomological outcomes with each dual ITN type in experimental hut trials can predict their epidemiological performance in the cRCT. CONCLUSION This study will provide information on the durability of two dual AI nets (Interceptor® G2 and Royal Guard®) in Benin and will help identify suitable methods for monitoring the durability of their insecticidal activity under operational conditions. The modelling component will determine the capacity of experimental hut trials to predict the epidemiological performance of dual AI nets across their lifespan.
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Affiliation(s)
- Corine Ngufor
- London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT, UK.
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin.
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin.
| | - Augustin Fongnikin
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin
| | - Josias Fagbohoun
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin
| | - Abel Agbevo
- London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT, UK
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin
| | - Thomas Syme
- London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT, UK
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin
| | - Juniace Ahoga
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin
| | - Manfred Accrombessi
- London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT, UK
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
| | - Natacha Protopopoff
- London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT, UK
| | - Jackie Cook
- London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT, UK
| | - Thomas S Churcher
- MRC Centre for Global Infectious Disease Analysis, Infectious Disease Epidemiology, Imperial College London, Norfolk Place, London, W2 1PG, UK
| | | | - Renaud Govoetchan
- London School of Hygiene and Tropical Medicine (LSHTM), London, WC1E 7HT, UK
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
- Panafrican Malaria Vector Research Consortium (PAMVERC), Cotonou, Benin
| | - Martin Akogbeto
- Centre de Recherches Entomologiques de Cotonou (CREC), Cotonou, Benin
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Bibbs CS, White GS, Rochlin I, Rivera A, Morris K, Wilson M, Schmitz M, Truttmann R, Dewsnup MA, Hardman J, Salt Q, Sorensen RB, Faraji A. Evaluation of An Aerial Application of Duet Hd® Against Aedes Dorsalis and Culex Tarsalis in Rural Habitats of the Great Salt Lake, Utah. JOURNAL OF THE AMERICAN MOSQUITO CONTROL ASSOCIATION 2023; 39:192-199. [PMID: 37665399 DOI: 10.2987/23-7126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/05/2023]
Abstract
The Salt Lake City Mosquito Abatement District (SLCMAD) has been conducting aerial applications using an organophosphate insecticide against adult mosquitoes for several decades. In order to evaluate a potential rotation product, aerial applications of Duet HD™, a pyrethroid, were conducted under operational conditions against wild populations of Aedes dorsalis and Culex tarsalis and against colony strains of Cx. pipiens and Cx. quinquefasciatus. The erratic wind patterns of the greater Salt Lake area did not prevent sufficient droplet deposition flux at 9 monitoring locations spread across a 5,120-acre (2,072 ha) spray block within rural habitats. Three separate aerial application trials showed great efficacy against Ae. dorsalis. In contrast, Cx. tarsalis exhibited inconsistent treatment-associated mortalities, suggesting the presence of less susceptible or resistant field populations as a result of spillover from agricultural or residential pyrethroid usage. Bottle bioassays to diagnose pyrethroid resistance using field-collected Cx. tarsalis indicated that some populations of this species, especially those closest to urban edges, failed to show adequate mortality in resistance assays. Despite challenging weather conditions, Duet HD worked reasonably well against susceptible mosquito species, and it may provide a crucial role as an alternative for organophosphate applications within specific and sensitive areas. However, its area-wide adoption into control applications by the SLCMAD could be problematic due to reduced impacts on the most important arboviral vector species, Cx. tarsalis, in this area. This study demonstrates the importance of testing mosquito control products under different operational environments and against potentially resistant mosquito populations by municipal mosquito control districts.
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Kont MD, Lambert B, Sanou A, Williams J, Ranson H, Foster GM, Lees RS, Churcher TS. Characterising the intensity of insecticide resistance: A novel framework for analysis of intensity bioassay data. CURRENT RESEARCH IN PARASITOLOGY & VECTOR-BORNE DISEASES 2023; 4:100125. [PMID: 37456558 PMCID: PMC10338328 DOI: 10.1016/j.crpvbd.2023.100125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/19/2023] [Revised: 06/09/2023] [Accepted: 06/11/2023] [Indexed: 07/18/2023]
Abstract
Insecticide resistance is a growing problem that risks harming the progress made by vector control tools in reducing the malaria burden globally. New methods for quantifying the extent of resistance in wild populations are urgently needed to guide deployment of interventions to improve disease control. Intensity bioassays measure mosquito mortality at a range of insecticide doses and characterise phenotypic resistance in regions where resistance is already detected. These data are increasingly being collected but tend to exhibit high measurement error and there is a lack of formal guidelines on how they should be analysed or compared. This paper introduces a novel Bayesian framework for analysing intensity bioassay data, which uses a flexible statistical model able to capture a wide variety of relationships between mortality and insecticide dose. By accounting for background mortality of mosquitoes, our approach minimises the impact of this source of measurement noise resulting in more precise quantification of resistance. It outputs a range of metrics for describing the intensity and variability in resistance within the sample and quantifies the level of measurement error in the assay. The functionality is illustrated with data from laboratory-reared mosquitoes to show how the lethal dose varies within and between different strains. The framework can also be used to formally test hypotheses by explicitly considering the high heterogeneity seen in these types of data in field samples. Here we show that the intensity of resistance (as measured by the median lethal dose (LC50) of insecticide) increases over 7 years in mosquitoes from one village in Burkina Faso but remains constant in another. This work showcases the benefits of statistically rigorous analysis of insecticide bioassay data and highlights the additional information available from this and other dose-response data.
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Affiliation(s)
- Mara D. Kont
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Imperial College London, Norfolk Place, London, W2 1PG, UK
| | - Ben Lambert
- Department of Mathematics and Statistics, University of Exeter, Exeter, EX4 4QJ, UK
| | - Antoine Sanou
- Centre National de Recherche et de Formation sur le Paludisme, Ouagadougou, Burkina Faso
| | - Jessica Williams
- Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, L3 5QA, UK
| | - Hilary Ranson
- Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, L3 5QA, UK
| | - Geraldine M. Foster
- Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, L3 5QA, UK
| | - Rosemary S. Lees
- Department of Vector Biology, Liverpool School of Tropical Medicine, Liverpool, L3 5QA, UK
| | - Thomas S. Churcher
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, Imperial College London, Norfolk Place, London, W2 1PG, UK
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12
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Devillers J, David JP, Barrès B, Alout H, Lapied B, Chouin S, Dusfour I, Billault C, Mekki F, Attig I, Corbel V. Integrated Plan of Insecticide Resistance Surveillance in Mosquito Vectors in France. INSECTS 2023; 14:insects14050457. [PMID: 37233085 DOI: 10.3390/insects14050457] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Revised: 04/26/2023] [Accepted: 05/06/2023] [Indexed: 05/27/2023]
Abstract
Mosquito-borne diseases such as malaria, dengue, or chikungunya have been re-emerging all over the world, including in Europe. Managing resistance to public health pesticides in mosquitoes is essential and requires global, integrated, and coordinated actions and strong engagement of decision-makers, scientists, and public health operators. In this context, the present work aims at proposing an integrated plan of resistance surveillance in France and in the French Overseas territories in order to provide graduated and appropriate responses according to the situation. Briefly, the plan relies on periodic monitoring of insecticide resistance at the population level in predefined sites using adequate biological, molecular, and/or biochemical approaches and a stratification of the level of resistance risk at the scale of territory to adjust surveillance and vector control actions. The plan relies on the latest methods and indicators used for resistance monitoring as recommended by the World Health Organization in order to prevent or slow down its extension in space and time. The plan has been developed for France but can be easily adapted to other countries in order to provide a coordinated response to the growing problem of mosquito resistance in Europe.
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Affiliation(s)
| | - Jean-Philippe David
- Laboratoire d'Ecologie Alpine, UMR UGA-USMB-CNRS 5553, Université Grenoble Alpes, 38041 Grenoble Cedex 9, France
| | - Benoit Barrès
- Université de Lyon, Anses, INRAE, USC CASPER, 69364 Lyon Cedex 7, France
| | - Haoues Alout
- ASTRE, UMR117 INRAE-CIRAD, 34398 Montpellier Cedex 5, France
| | - Bruno Lapied
- Université Angers, INRAE, SIFCIR, SFR QUASAV, 49045 Angers Cedex, France
| | - Sébastien Chouin
- Conseil Départemental de la Charente-Maritime, DEM, Démoustication, 17076 La Rochelle, France
| | - Isabelle Dusfour
- Institut de Recherche pour le Développement (IRD), MIVEGEC, Univ. Montpellier, CNRS, IRD, 34394 Montpellier, France
| | | | | | | | - Vincent Corbel
- Institut de Recherche pour le Développement (IRD), MIVEGEC, Univ. Montpellier, CNRS, IRD, 34394 Montpellier, France
- Laboratório de Fisiologia e Controle de Artrópodes Vetores (Laficave), Instituto Oswaldo Cruz (IOC), Fundacao Oswaldo Cruz (FIOCRUZ), Rio de Janeiro CEP 21040-360, Brazil
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13
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Odjo EM, Salako AS, Padonou GG, Yovogan B, Adoha CJ, Adjottin B, Sominahouin AA, Sovi A, Osse R, Kpanou CD, Sagbohan HW, Djenontin A, Agbangla C, Akogbeto MC. What can be learned from the residual efficacy of three formulations of insecticides (pirimiphos-methyl, clothianidin and deltamethrin mixture, and clothianidin alone) in large-scale in community trial in North Benin, West Africa? Malar J 2023; 22:150. [PMID: 37158866 PMCID: PMC10165746 DOI: 10.1186/s12936-023-04572-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Accepted: 04/24/2023] [Indexed: 05/10/2023] Open
Abstract
BACKGROUND In Alibori and Donga, two departments of high malaria incidence of Northern Benin, pirimiphos-methyl, mixture deltamethrin + clothianidin, as well as clothianidin were used at large scale for IRS. The present study aimed to assess the residual efficacy of these products. METHODS Immatures of Anopheles gambiae sensu lato (s.l.) collected in the communes of Kandi and Gogounou (Department of Alibori), Djougou and Copargo (Department of Donga) were reared until adulthood. Females aged 2-5 days were used for susceptibility tube tests following the WHO protocol. The tests were conducted with deltamethrin (0.05%), bendiocarb (0.1%), pirimiphos-methyl (0.25%) and clothianidin (2% weight per volume). For cone tests performed on cement and mud walls, the An. gambiae Kisumu susceptible strain was used. After the quality control of the IRS performed 1-week post-campaign, the evaluation of the residual activity of the different tested insecticides/mixture of insecticides was conducted on a monthly basis. RESULTS Over the three study years, deltamethrin resistance was observed in all the communes. With bendiocarb, resistance or possible resistance was observed. In 2019 and 2020, full susceptibility to pirimiphos-methyl was observed, while possible resistance to the same product was detected in 2021 in Djougou, Gogounou and Kandi. With clothianidin, full susceptibility was observed 4-6 days post-exposure. The residual activity lasted 4-5 months for pirimiphos-methyl, and 8-10 months for clothianidin and the mixture deltamethrin + clothianidin. A slightly better efficacy of the different tested products was observed on cement walls compared to the mud walls. CONCLUSION Overall, An. gambiae s.l. was fully susceptible to clothianidin, while resistance/possible resistance was observed the other tested insecticides. In addition, clothianidin-based insecticides showed a better residual activity compared to pirimiphos-methyl, showing thus their ability to provide an improved and prolonged control of pyrethroid resistant vectors.
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Affiliation(s)
- Esdras Mahoutin Odjo
- Centre de Recherche Entomologique de Cotonou, Cotonou, Benin.
- Faculté des Sciences et Techniques de l'Université d'Abomey-Calavi, Abomey-Calavi, Benin.
| | | | - Germain Gil Padonou
- Centre de Recherche Entomologique de Cotonou, Cotonou, Benin
- Faculté des Sciences et Techniques de l'Université d'Abomey-Calavi, Abomey-Calavi, Benin
| | - Boulais Yovogan
- Centre de Recherche Entomologique de Cotonou, Cotonou, Benin
- Faculté des Sciences et Techniques de l'Université d'Abomey-Calavi, Abomey-Calavi, Benin
| | - Constantin Jésukèdè Adoha
- Centre de Recherche Entomologique de Cotonou, Cotonou, Benin
- Faculté des Sciences et Techniques de l'Université d'Abomey-Calavi, Abomey-Calavi, Benin
| | - Bruno Adjottin
- Centre de Recherche Entomologique de Cotonou, Cotonou, Benin
- Faculté des Sciences et Techniques de l'Université d'Abomey-Calavi, Abomey-Calavi, Benin
| | | | - Arthur Sovi
- Centre de Recherche Entomologique de Cotonou, Cotonou, Benin
- Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK
- Faculté d'Agronomie de l'Université de Parakou, Parakou, Benin
| | - Razaki Osse
- Centre de Recherche Entomologique de Cotonou, Cotonou, Benin
- Université Nationale d'Agriculture de Porto-Novo, Porto-Novo, Benin
| | - Casimir D Kpanou
- Centre de Recherche Entomologique de Cotonou, Cotonou, Benin
- Faculté des Sciences et Techniques de l'Université d'Abomey-Calavi, Abomey-Calavi, Benin
| | - Hermann W Sagbohan
- Centre de Recherche Entomologique de Cotonou, Cotonou, Benin
- Faculté des Sciences et Techniques de l'Université d'Abomey-Calavi, Abomey-Calavi, Benin
| | - Armel Djenontin
- Centre de Recherche Entomologique de Cotonou, Cotonou, Benin
- Faculté des Sciences et Techniques de l'Université d'Abomey-Calavi, Abomey-Calavi, Benin
| | - Clement Agbangla
- Centre de Recherche Entomologique de Cotonou, Cotonou, Benin
- Direction Générale de la Recherche Scientifique, Ministère de l'Enseignement Supérieur et de la Recherche Scientifique, Cotonou, Benin
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Fouet C, Ashu F, Ambadiang M, Tchapga W, Wondji C, Kamdem C. Resistance to clothianidin reduces the efficacy of SumiShield ® 50WG, a neonicotinoid formulation for indoor residual spraying, against Anopheles gambiae. RESEARCH SQUARE 2023:rs.3.rs-2847231. [PMID: 37162950 PMCID: PMC10168466 DOI: 10.21203/rs.3.rs-2847231/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Chronic exposure of mosquito larvae to pesticide residues in agricultural areas is often associated with evolution of resistance to insecticides used for vector control. This presents a concern for the efficacy of clothianidin, an agricultural neonicotinoid qualified for Indoor Residual Spraying (IRS). Using standard bioassays, we tested if reduced susceptibility to clothianidin affects the efficacy of SumiShield® 50WG, one of the two newly approved formulations, which contains 50% clothianidin. We simultaneously monitored susceptibility to clothianidin and to SumiShield® 50WG, testing adults of Anopheles gambiae, An. coluzzii and Culex sp collected from urban, suburban and agricultural areas of Yaoundé. We found that the level of susceptibility to the active ingredient predicted the efficacy of SumiShield® 50WG. This formulation was very potent against populations that achieved 100% mortality within 72 h of exposure to a discriminating dose of clothianidin. By contrast, mortality leveled off at 75.4 ± 3.5% within 7 days of exposure to SumiShield® 50WG in An. gambiae adults collected from a farm where spraying of acetamiprid and imidacloprid is driving cross-resistance to clothianidin. These findings indicate that more potent formulations of clothianidin or different insecticides should be prioritized in areas where resistance is emerging.
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Ashu FA, Fouet C, Ambadiang MM, Penlap-Beng V, Kamdem C. Vegetable oil surfactants are synergists that can bias neonicotinoid susceptibility testing in adult mosquitoes. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.18.537421. [PMID: 37131639 PMCID: PMC10153115 DOI: 10.1101/2023.04.18.537421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Background The standard operating procedure for testing the susceptibility of adult mosquitoes to clothianidin, a neonicotinoid, recommends using a vegetable oil ester as surfactant. However, it has not yet been determined if the surfactant is an inert ingredient or if it can act as a synergist and bias the test. Methodology/Principal Findings Using standard bioassays, we tested the synergistic effects of a vegetable oil surfactant on a spectrum of active ingredients including four neonicotinoids (acetamiprid, clothianidin, imidacloprid and thiamethoxam) and two pyrethroids (permethrin and deltamethrin). Three different formulations of linseed oil soap used as surfactant were far more effective than the standard insecticide synergist piperonyl butoxide in enhancing neonicotinoid activity in Anopheles mosquitoes. At the concentration used in the standard operating procedure (1% v/v), vegetable oil surfactants lead to more than 10-fold reduction in lethal concentrations, LC 50 and LC 99 , of clothianidin in a multi-resistant field population and in a susceptible strain of Anopheles gambiae . At 1% or 0.5% (v/v), the surfactant restored susceptibility to clothianidin, thiamethoxam and imidacloprid and increased mortality to acetamiprid from 43 ± 5.63% to 89 ± 3.25% (P<0.05) in resistant mosquitoes. By contrast, linseed oil soap had no effect on the level of resistance to permethrin and deltamethrin suggesting that the synergism of vegetable oil surfactants may be specific to neoniconoids. Conclusions/Significance Our findings indicate that vegetable oil surfactants are not inert ingredients in neonicotinoid formulations, and their synergistic effects undermine the ability of standard testing procedures to detect early stages of resistance.
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