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


RESULTS
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).


CONCLUSIONS
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.
Farenhorst
Marit
M
Laboratory of Entomology, Wageningen University and Research Center, Wageningen, The Netherlands. marit.farenhorst@wur.nl
Knols
Bart G J
BG
Thomas
Matthew B
MB
Howard
Annabel F V
AF
Takken
Willem
W
Rowland
Mark
M
N'Guessan
Raphael
R
D000818:Animals; D000852:Anopheles / Q000235:genetics / Q000382:microbiology*; D052982:Beauveria / Q000502:physiology*; D003634:DDT; D005260:Female; D005786:Gene Expression Regulation; D007300:Insect Control / Q000379:methods*; D007305:Insecticide Resistance / Q000235:genetics; D007306:Insecticides; D007753:Laboratories; D052981:Metarhizium / Q000502:physiology*; D057147:Mosquito Nets; D026023:Permethrin; D016019:Survival Analysis; D013997:Time Factors
D007306:Insecticides; D026023:Permethrin; D003634:DDT