Synergy in efficacy of fungal entomopathogens and permethrin against West African insecticide-resistant Anopheles gambiae mosquitoes

• Published in: PloS one 2010-08, Vol.5 (8), p.e12081
• Main Authors: Farenhorst, Marit, Knols, Bart G J, Thomas, Matthew B, Howard, Annabel F V, Takken, Willem, Rowland, Mark, N'Guessan, Raphael
• Format: Article
• Language: English
• Subjects: Animals; Anopheles; Anopheles - genetics; Anopheles - microbiology; Anopheles gambiae; Antifungal agents; Aquatic insects; Beauveria; Beauveria - physiology; Beauveria bassiana; biopesticides; Blattaria; Boophilus microplus; coleoptera; Colonies; culex-quinquefasciatus; Culicidae; Cydnidae; Cyrtomenus; DDT; Deuteromycotina; Disease transmission; Drug dosages; Enzymes; Evolution; Exposure; Female; Fungi; Gene Expression Regulation; Health aspects; Hemiptera; infection; Infections; Infectious Diseases; Infectious Diseases/Epidemiology and Control of Infectious Diseases; Infectious Diseases/Neglected Tropical Diseases; Insect Control - methods; Insecticide resistance; Insecticide Resistance - genetics; Insecticides; knockdown; Laboratories; Malaria; malaria mosquitos; Metabolism; Metarhizium; Metarhizium - physiology; Metarhizium anisopliae; Mortality; Mosquito Nets; Mosquitoes; Mycoses; Permethrin; Pesticide resistance; Pesticides; pyrethroid resistance; Pyrethroids; Studies; Survival; Survival Analysis; Sustainable development; Sustainable use; Synergism; Synergistic effect; Synergistic effects; Time Factors; Vector-borne diseases; Vectors
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0012081

Increasing incidences of insecticide resistance in malaria vectors are threatening the sustainable use of contemporary chemical vector control measures. Fungal entomopathogens provide a possible additional tool for the control of insecticide-resistant malaria mosquitoes. This study investigated the compatibility of the pyrethroid insecticide permethrin and two mosquito-pathogenic fungi, Beauveria bassiana and Metarhizium anisopliae, against a laboratory colony and field population of West African insecticide-resistant Anopheles gambiae s.s. mosquitoes. A range of fungus-insecticide combinations was used to test effects of timing and sequence of exposure. Both the laboratory-reared and field-collected mosquitoes were highly resistant to permethrin but susceptible to B. bassiana and M. anisopliae infection, inducing 100% mortality within nine days. Combinations of insecticide and fungus showed synergistic effects on mosquito survival. Fungal infection increased permethrin-induced mortality rates in wild An. gambiae s.s. mosquitoes and reciprocally, exposure to permethrin increased subsequent fungal-induced mortality rates in both colonies. Simultaneous co-exposure induced the highest mortality; up to 70.3+/-2% for a combined Beauveria and permethrin exposure within a time range of one gonotrophic cycle (4 days). Combining fungi and permethrin induced a higher impact on mosquito survival than the use of these control agents alone. The observed synergism in efficacy shows the potential for integrated fungus-insecticide control measures to dramatically reduce malaria transmission and enable control at more moderate levels of coverage even in areas where insecticide resistance has rendered pyrethroids essentially ineffective.