Pathogenicity of Evlachovaea sp (Hyphomycetes), a new species isolated from Triatoma sordida, in Chagas' disease vectors

Patogenicidade de Evlachovaea sp (Hyphomycetes), uma nova espécie isolada de Triatoma sordida, para vetores da doença de Chagas

COMUNICAÇÃO COMMUNICATION

Pathogenicity of Evlachovaea sp (Hyphomycetes), a new species isolated from Triatoma sordida, in Chagas' disease vectors

Patogenicidade de Evlachovaea sp (Hyphomycetes), uma nova espécie isolada de Triatoma sordida, para vetores da doença de Chagas

Christian Luz; Luiz Fernando Nunes Rocha; Ionizete Garcia Silva

Institute of Tropical Pathology and Public Health, Federal University of Goiás, Goiânia, GO, Brazil

^{Correspondence}

ABSTRACT

Evlachovaea sp was tested on nymphs of 5 Triatoma spp 5 Rhodnius spp, Panstrongylus herreri and Dipetalogaster maximus at 25°C, 75% humidity and humidity >98%. Most species showed susceptibility to fungal infection at high humidity. Mortality was reduced at 75% humidity. Fungal development was observed on 69.5% of cadavers.

Key-words:Evlachovaea. Triatominae. Pathogenicity. Vector control.

RESUMO

Evlachovaea sp foi testada em ninfas de 5 Triatoma spp, 5 Rhodnius spp, Panstrongylus herreri e Dipetalogaster maximus a 25°C, 75% umidade e umidade >98%. A maioria das espécies foi suscetível à infecção em umidade alta. Mortalidade foi reduzida a 75% de umidade. O fungo desenvolveu em 69.5% dos cadáveres.

Palavras-chaves:Evlachovaea. Triatominae. Patogenicidade. Controle de vetores.

Entomopathogenic fungi such as Beauveria bassiana and Metarhizium anisopliae were shown to be active against triatomine bugs under laboratory conditions^{2 4}. However, only a few field tests have been reported, and there is almost no published information about pathogenic fungi isolated from field-collected triatomine cadavers. Parameswaran and Sankaran (1979) reported B. bassiana on the triatomine bug Linshcosteus sp in India. Recently another fungus identified as a new species of Evlachovaea, a genus described in Russia¹, was found on a dead Triatoma sordida nymph in central Brazil, and its pathogenicity was documented against Triatoma infestans³. Herein we report results on the pathogenicity of the Evlachovaea sp in other triatomine species.

All triatomines tested, 5 Triatoma spp, 5 Rhodnius spp, Panstrongylus herreri, and Dipetalogaster maximus, originated from the Institute of Tropical Pathology and Public Health, Goiânia, Brazil. Insects were reared at 25 ± 0.5°C, 75 ± 5% relative humidity (RH), and a photoperiod of 12:12 (L:D) h. They were blood-fed on chickens at 2-week intervals. The fungus was cultivated on complete medium and incubated for 15 days at 25 ± 0.5°C, 75 ± 5% RH, and a photoperiod of 12:12 (L:D) h³. For the tests, conidia were suspended in 10ml of sterile 0.1% Tween 80 and adjusted to 3.3x10⁶, 10⁷, 3.3x10⁷, 10⁸, 3.3x10⁸ and 10⁹ conidia/ml, corresponding to between 2.4x10³ and 8.0x10⁵ CFU (colony-forming unit)/cm² treated surface⁴. Ten recently molted and unfed third instar nymphs (N3) of the various species were directly sprayed with 5ml of each concentration using a Potter spray tower (Burkard Ltd., Hertfordshire, UK). Control insects were treated with 0.1% Tween 80 only. N3 were placed on filter paper in plastic Petri dishes (90 x15mm) and then incubated in a test chamber (33 x 37 x 22cm) at RH 75%, humidity close to saturation (RH>98%), 25 ± 0.5°C and a photoperiod of 12:12 (L:D) h. Humidity of 75% inside the test chamber was regulated with a saturated solution of NaCl. Insects were not fed during the assays. Mortality of nymphs was monitored daily. Lethal concentrations to kill 50% and 90% (LC₅₀ and LC₉₀) were calculated by probit analysis. Cadavers were placed in Petri dishes and incubated at RH>98% and 25°C during 20 days. Fungal emergence of Evlachovaea sp on cadavers and external conidiogenesis were examined daily.

Most triatomine species tested were found susceptible to the Evlachovaea sp isolate at RH>98%. Susceptibility of insects was clearly influenced by humidity. At RH 75% mortality was distinctly reduced for all species. Results showed a general relationship between dosage and fungal activity against insects. This was also observed for T. infestans³. First insects of most triatomine species succumbed to the fungus 5-7 days after application of ³3.3x10⁷ conidia/ml independently of humidity tested. Mortality of T. vitticeps and T. delpontei initiated after 8 and 9 days incubation at RH>98%, respectively, and the first dead N3 of T. picturata exposed to RH 75% were found 12 days after treatment. Total mortality was observed at the highest doses (3.3x10⁸ and 10⁹ conidia/ml) and humidity close to saturation, except for T. vitticeps, T. picturata and T. sordida which had mortality rates of 10%, 60% and 80%, respectively, 20 days after exposure at RH>98%. Values of LC₅₀, and LC₉₀ are presented in Table 1. LC₅₀, 15 days after incubation at RH>98%, varied from 3.18x10³ CFU/cm² (R. neglectus) to 4.34x10⁵ CFU/cm² (T. sordida). At RH 75% only P. herreri (1.37x10⁵ CFU/cm²) and R. ecuadoriensis (3.11x10⁵ CFU/cm²) presented sufficient mortality to calculate the LC₅₀. After 20 days incubation at humidity close to saturation mortality of T. delpontei, R. neglectus, R. nasutus and D. maximus were too high to calculate LC₅₀ and varied between 2.93x10³ CFU/cm² (R. prolixus) and 1.44x10⁵ CFU/cm² (T. picturata) for the other species. At RH 75% LC₅₀ 20 days after incubation was 1.12x10⁵ CFU/cm², 1.68x10⁵ CFU/cm² and 3.71x10⁵ CFU/cm² for P. herreri, R. ecuadoriensis and D. maximus, respectively (Table 1). Control mortality at both humidities was £10% during the assay, irrespective of the species.

Among all cadavers regardless of triatomine species, humidity or dose tested, 50.8% of the cadavers showed outgrowth of Evlachovaea sp only, 18.7% were found with mixed development of Evlachovaea sp and other saprophytic fungi, 25% with unidentified saprophytic fungi, and 5.5% showed no external fungi. Results underline the need to study entomopathogenic fungi for control of triatomine bugs.

ACKNOWLEDGEMENTS

Authors thank Carmeci N Elias for technical support, and Richard A Humber for the critical review of the manuscript.

Recebido para publicação em 30/6/2003

Aceito em 3/2/2004

This work was supported by CNPq Centro-Oeste (Conselho Nacional de Desenvolvimento Científico e Tecnológico).

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Publication Dates

• Publication in this collection
  12 Apr 2004
• Date of issue
  Mar 2004

History

• Received
  30 June 2003
• Accepted
  03 Feb 2004