Extracellular extracts of antagonistic fungi,Trichoderma longibrachiatum and Trichoderma viride, as larvicides against dengue vectors, Aedes aegypti and Aedes albopictus

Abstract

Aedes aegypti and Aedes albopictus are the responsible vectors of transmitting dengue in Sri Lanka. Excessive use of chemical pesticides causes insecticide resistance. Therefore, mosquito biolarvicides remain to be an important method for mosquito control. The use of fungal metabolites can be considered a tool to overcome the issues related to insecticide resistance and environmental pollution. The present study focused on the evaluation of the mosquito larvicidal efficacy of Trichoderma longibrachiatum and Trichoderma viride aqueous and crude extracellular metabolites against Ae.aegypti and Ae.albopictus under the laboratory conditions. Fungi were grown in Richards' broth medium for collection of fungal biomass. Eight test concentrations of extracellular aqueous and crude fungal filtrates in a range from 12.5 gL−1 to 175 gL−1 were prepared and batches of 25 laboratory-reared third instar larvae of Ae.aegypti and Ae.albopictus were exposed to each test concentration separately with three replicates. Control bioassays were conducted with distilled water and larval mortality was recorded after 24 hours and 48 hours of exposure periods.The study revealed that LC50 values and LC90 values for extracellular crude metabolites for two fungal species were lower than the values obtained for extracellular aqueous extracts. All the LC50 values obtained for Ae.albopictus were lower than that of Ae.aegypti. LC50 values obtained for T.viride aqueous extracellular metabolites were 81.46 gL−1 and 87.75 gL−1in 24 hours, 70.66 gL-1 and 77.93 gL−1 in 48 hours for Ae. albopictus and Ae. aegypti respectively. LC50 values obtained for T.longibrachiatum aqueous extracellular metabolites were recorded as 103.35gL−1 and 108.79gL−1 in 24 hours and 93.05gL−1 and 102.1gL−1 in 48 hours for Ae.albopictus and Ae.aegypti respectively. It was revealed that LC50 values obtained for T.viride crude extracellular metabolites were 34.42gL−1 and 47.27gL−1 in 24 hours, 30.29gL−1 and 41.56gL−1 in hours for Ae.albopictus and Ae.aegypti respectively. LC50 values obtained for T.longibrachiatum crude extracellular metabolites were 49.84gL−1 and 59.24gL−1 in 24 hours, 40.73gL−1 and 51.49gL−1 in 48 hours for Ae.albopictus and Ae.aegypti respectively. It can be concluded that there is a potential for using T.viride as an effective larvicide against dengue mosquitoes.