Dissemination of Metarhizium anisopliae of low and high virulence by mating behavior in Aedes aegypti

Abstract

BackgroundDengue is a viral disease transmitted by Aedes mosquitoes. It is a threat for public health worldwide and its primary vector Aedes aegypti is becoming resistant to chemical insecticides. These factors have encouraged studies to evaluate entomopathogenic fungi against the vector. Here we evaluated mortality, infection, insemination and fecundity rates in A. aegypti females after infection by autodissemination with two Mexican strains of Metarhizium anisopliae.MethodsTwo M. anisopliae strains were tested: The Ma-CBG-1 least virulent (lv), and the Ma-CBG-2 highly virulent (hv) strain. The lv was tested as non mosquito-passed (NMP), and mosquito-passed (MP), while the hv was examined only as MP version, therefore including the control four treatments were used. In the first bioassay virulence of fungal strains towards female mosquitoes was determined by indirect exposure for 48 hours to conidia-impregnated paper. In the second bioassay autodissemination of fungal conidia from fungus-contaminated males to females was evaluated. Daily mortality allowed computation of survival curves and calculation of the LT50 by the Kaplan-Meier model. All combinations of fungal sporulation and mating insemination across the four treatments were analyzed by χ2. The mean fecundity was analyzed by ANOVA and means contrasted with the Ryan test.ResultsIndirect exposure to conidia allowed a faster rate of mortality, but exposure to a fungal-contaminated male was also an effective method of infecting female mosquitoes. All females confined with the hv strain-contaminated male died in fifteen days with a LT50 of 7.57 (± 0.45) where the control was 24.82 (± 0.92). For the lv strain, it was possible to increase fungal virulence by passing the strain through mosquitoes. 85% of females exposed to hv-contaminated males became infected and of them just 10% were inseminated; control insemination was 46%. The hv strain reduced fecundity by up to 99%, and the lv strain caused a 40% reduction in fecundity.ConclusionsThe hv isolate infringed a high mortality, allowed a low rate of insemination, and reduced fecundity to nearly zero in females confined with a fungus-contaminated male. This pathogenic impact exerted through sexual transmission makes the hv strain of M. anisopliae worthy of further research.

Vectorial Capacity of Aedes aegypti for Dengue Virus Type 2 Is Reduced with Co-infection of Metarhizium anisopliae

“…Similarly, this competition for nutrients between the host and fungus, could also explain the 52% reduction in fecundity and a shortening of the GC from 5 to 3 days in B3. In a previous study, we conducted with this fungus but with a highly virulent strain (Ma-CBG-2) found that in mycosed females the fecundity was reduced to almost zero [7]. In addition, the Anopheles gambiae female mosquitoes tend to take smaller blood meals after becoming fungus-infected [29], [30] and this also plausibly explains the reduced number of females which actually laid eggs.…”

“…aegypti mosquitoes were exposed to single infections of either Ma-CBG-1 M. anisopliae strain at 1.6×10 8 conidia mL −1 (SF) or DENV-2 (SV); and both fungus and virus (CI). Fungal infections were done as described previously [7]. For the virus infections, females were confined in 1-liter glass flasks, and were fed on 2,320 µL defibrinated human blood and 680 µL of virus suspension containing a titer of 1×10 7 plaque-forming units (PFU) mL −1 , for 1 hour via a water-jacketed membrane feeding apparatus [16].…”

“…aegypti and Aedes albopictus [3]. The successful infection of adult female mosquitoes has been made via direct contact [4], [5] and also via auto-dissemination from males to females when mating [6], [7].…”

New insights on the effectiveness of Metarhizium anisopliae formulation and application against Aedes aegypti eggs

“…Conidia could eventually be dispersed by contaminated females that leave the fungus‐infested substrate after oviposition (Reyes‐Villanueva et al . ).…”

Evaluating the lethal and pre-lethal effects of a range of fungi against adult Anopheles stephensi mosquitoes

“…To date around forty experimental studies have been reported examining some aspect of fungal infection on adult mosquito vectors [12,13,15-19,21-24,31-57]. These studies include multiple fungal isolates from eight genera and twenty-one species.…”