Biological Control of the Chagas Disease Vector Triatoma infestans with the Entomopathogenic Fungus Beauveria bassiana Combined with an Aggregation Cue: Field, Laboratory and Mathematical Modeling Assessment.

BACKGROUND: Current Chagas disease vector control strategies, based on chemical insecticide spraying, are growingly threatened by the emergence of pyrethroid-resistant Triatoma infestans populations in the Gran Chaco region of South America. METHODOLOGY AND FINDINGS: We have already shown that the entomopathogenic fungus Beauveria bassiana has the ability to breach the insect cuticle and is effective both against pyrethroid-susceptible and pyrethroid-resistant T. infestans, in laboratory as well as field assays. It is also known that T. infestans cuticle lipids play a major role as contact aggregation pheromones. We estimated the effectiveness of pheromone-based infection boxes containing B. bassiana spores to kill indoor bugs, and its effect on the vector population dynamics. Laboratory assays were performed to estimate the effect of fungal infection on female reproductive parameters. The effect of insect exuviae as an aggregation signal in the performance of the infection boxes was estimated both in the laboratory and in the field. We developed a stage-specific matrix model of T. infestans to describe the fungal infection effects on insect population dynamics, and to analyze the performance of the biopesticide device in vector biological control. CONCLUSIONS: The pheromone-containing infective box is a promising new tool against indoor populations of this Chagas disease vector, with the number of boxes per house being the main driver of the reduction of the total domestic bug population. This ecologically safe approach is the first proven alternative to chemical insecticides in the control of T. infestans. The advantageous reduction in vector population by delayed-action fungal biopesticides in a contained environment is here shown supported by mathematical modeling.

Toxicological and biochemical response of the entomopathogenic fungus Beauveria bassiana after exposure to deltamethrin.

BACKGROUND: The chemical control of the Chagas disease vector Triatoma infestans is endangered by the emergence of pyrethroid resistance. An effective alternative control tool is the use of the entomopathogenic fungus Beauveria bassiana. The effect of deltamethrin on fungal growth, gene expression and enzyme activity in relation to detoxification, antioxidant response and oxidative stress levels was studied to evaluate fungal tolerance to deltamethrin. RESULTS: The mean inhibitory concentration (IC50 ) was 50 µg deltamethrin/cm(2). Cytochrome P450 genes were differentially expressed; cyp52X1 and cyp617N1 transcripts were > 2-fold induced, followed by cyp655C1 (1.8-fold). Minor effects were observed on genes encoding for other P450s, epoxide hydrolase and glutathione S-transferase (GST). Superoxide dismutase (SOD) genes showed induction levels ≤ 2, catalase (CAT) and glutathione peroxidase genes were also induced ∼ 2-3-fold and < 2-fold, respectively. The activities of enzymes participating in the antioxidant defense system and phase II detoxification were also evaluated; SOD, CAT and GST activity showed significant differences with deltamethrin concentration. Lipid peroxidation levels and free proline content were also altered. CONCLUSIONS: Beauveria bassiana GHA can be used combined with deltamethrin without significant metabolic detrimental effects. This combination will help optimizing the benefits and increasing the efficacy of vector control tools.

Contribution of the horizontal transmission of the entomopathogenic fungus Beauveria bassiana to the overall performance of a fungal powder formulation against Triatoma infestans.

Control of domiciliated Triatoma infestans, the major Chagas disease vector in southern South America, is currently achieved by indoor residual spraying of infested houses with chemical insecticides. However, in recent years this strategy has been threatened by the emergence of pyrethroid-resistant bug populations. As an alternative approach, we have previously demonstrated the efficacy of the entomopathogenic fungus Beauveria bassiana to control T. infestans bugs regardless of their pyrethroid susceptibility. In this work, we tested the virulence and residual activity of a powdered fungal formulation, and studied the significance of the horizontal transmission process (autodissemination) to fungal infection of bugs. The B. bassiana-based formulation was highly virulent against all T. infestans stages, and maintained its insecticidal capability for at least 5 months under natural ambient conditions. We showed that horizontal transmission of conidia is associated to bug density, and contributes significantly to the overall population infection event.