Control of Triatoma infestans (Klug) (Reduviidae: Triatominae) with Beauveria bassiana (Bals.) Vuill.: preliminary assays on formulation and application in the field

Abstract

Beauveria bassiana (Bals.) Vuill., isolate CG 306, was assayed against Triatoma infestans (Klug) using indirect application by contact with a treated filter paper. The fungus was deposited on filter paper by vacuum-filtration of a conidial suspension. Estimates of 50% survival time of insects were between 15 and 21 days at 3x10(6) and 10(7) conidia/cm² of treated support, respectively, without significant difference between concentrations. A concentration of 2.4x10(6) conidia/cm² of CG 306 was necessary to kill 50% of T. infestans third instar nymphs 25 days after inoculation at 25°C and 50% relative humidity, when insects were continuously exposed to conidia. The LC50 was significantly higher (2.0x10(7) conidia/cm²) when insects were exposed for 1 h to the treated filter paper, than with continuous exposure. A mineral oil based emulsifier (2%) had no effect on germination of conidia in vitro. Fewer formulated conidia were necessary to kill 50% of insects after constant exposure to the treated surface, compared with unformulated conidia. After a 1 h exposure, unformulated conidia were more effective than formulated. After spraying B. bassiana (10(7) conidia/cm²) and releasing third instar nymphs of T. infestans in small wooden test houses, the rate of insect recovery after 25 days was significantly lower in the fungus treated houses compared to the control house. Mortality due to fungal infection of recovered insects transferred to the laboratory was between 38.1 and 93.8%, compared with no mortality in the control group. The rate of mortality of insects exposed to treated filter paper in gauze covered cups in the houses was between 35 and 78.8% after 25 days. Persistence of conidia on filter paper exposed inside the houses was > 98% during the field tests. There was no development of CG 306 on cadavers originating from laboratory infection and exposed to field conditions in the houses.

Potential for entomopathogenic fungi to control Triatoma dimidiata (Hemiptera: Reduviidae), a vector of Chagas disease in Mexico

“…The LC 50 was signifi cantly higher (2.0x10 7 conidia/ cm 2 ) when insects were exposed for 1 h to treated fi lter paper 39 . In another study, a fungal suspension was used to inoculate T. infestans adults; insects were individually submerged in a 5-ml suspension of B. bassiana at 10 7 conidia/ml for 7 seconds…”

“…Several experiments have documented the efficacy of entomopathogenic fungi, such as Beauveria bassiana and Metarhizium anisopliae, in the control of Chagas disease vectors under laboratory [24][25][26][27][28] and fi eld conditions [29][30][31][32] . The fi rst barrier to the penetration of contact insecticides is the insect cuticle, and an increase in the thickness of the Triatoma infestans cuticle was found to be associated with the resistance of this insect to pyrethroids.…”

“…This may explain why T. fl avus did not grow in treated insects in our study. Low humidity has been reported to be responsible for the failure of B. bassiana to emerge from the corpses of treated T. infestans 38,39 .…”

Insecticide resistance in vector Chagas disease: Evolution, mechanisms and management

“…Several strains were evaluated against several of triatomine species (e.g. T. infestans, T sordida, R. prolixus, Meccus pallidipennis) (Luz et al, 1999(Luz et al, , 2004Pedrini et al, 2009;Forlani et al, 2011;Zumaquero-Ríos et al, 2014). Results from laboratory and field studies using powder formulation or mineral-oil base formulation, confirm that B. bassiana is a promising candidate to control T. infestans (Luz et al, 1999;Pedrini et al, 2009;Forlini et al, 2011).…”

SELEÇÃO DE ISOLADOS DE FUNGOS ENTOMOPATOGÊNICOS PARA O CONTROLE DE Hedypathes betulinus E AVALIAÇÃO DA PERSISTÊNCIA

“…De acordo com Luz et al (1999), o desenvolvimento das formulações à base de óleo dos fungos entomopatogênicos é uma estratégia para preservá-los dos efeitos ambientais negativos. As formulações de fungos entomopatogênicos à base de óleo são superiores àquelas à base de água, especialmente em locais onde a umidade é baixa (BATEMAN et al, 1993).…”