Luiz F.N. Rocha

Ovicidal Activity of Entomopathogenic Hyphomycetes on Aedes aegypti (Diptera: Culicidae) Under Laboratory Conditions

Abstract The ovicidal activity of 21 hyphomycete fungi species against Aedes aegypti (L.) (Diptera: Culicidae) was tested. Fungi with ovicidal activity developed on high numbers of eggs (≥70%) during 25 d of exposure. A clear ovicidal activity with low values of hatch (1.3–40%) was observed after 25 d of incubation with Isaria farinosa (Holm: Fries) Fries, Paecilomyces carneus (Duché & Heim) Brown & Smith, Paecilomyces marquandii (Massee) Hughes, Isaria fumosorosea (Wize), Metarhizium anisopliae (Metschnikoff) Sorokin, Penicillium sp., Paecilomyces lilacinus (Thom) Samson, Beauveria bassiana (Balsamo) Vuillemin, and Evlachovaea kintrischica Borisov & Tarasov. More than 63% of eggs hatched after 25-d exposures to 11 other fungi species deemed as ineffective. These are the first results to show the effects of entomopathogenic fungi against eggs of Ae. aegypti, and they suggest their potential as control agents of this vector.

Occurrence of Metarhizium spp. in Central Brazilian soils.

The biodiversity of entomopathogenic fungi in tropical ecosystems is still little investigated, and the objective of this study was to isolate and identify fungi of the entomopathogenic genus Metarhizium (Hypocreales: Clavicipitaceae) present in undisturbed soils of the Central Brazilian Cerrado. A total of 107 Metarhizium isolates was obtained from soils collected from Cerrado sites in the state of Goiás; gene sequences from 63 of these were obtained and compared. Among these, one was confirmed to be M. anisopliae sensu stricto; 53 were very closely allied to M. anisopliae but require more extensive genetic characterization to determine if they might represent a new taxon in the M. anisopliae species complex. Eight of these Cerrado isolates were referable to M. robertsii, and the remaining isolate is the first South American (and Southern Hemisphere) collection of M. flavoviride var. pemphigi. These findings underline the need for better characterization of the diversity of these widely distributed fungi in Brazil.

Activity of oil-formulated Beauveria bassiana against Triatoma sordida in peridomestic areas in Central Brazil.

Field tests were carried out during the rainy season of 2001/2002 in São Luís de Montes Belos, Goiás, Brazil, to evaluate the potential of the entomopathogenic fungus, Beauveria bassiana, against peridomestic Triatoma sordida. An oil-water formulation of the isolate CG 14 (Embrapa) was applied in triatomine infested hen houses of four farms at a final concentration of 10(6) conidia/cm2. Numbers of T. sordida decreased over the next 25 days, after application of the fungus, and B. bassiana developed on dead insects in one hen house. A high number of B. bassiana colonies was detected in substrates collected in treated hen houses 24 h after application of CG 14. In the following three months the presence of B. bassiana declined to values found before treatment.

Detection of entomopathogenic fungi in peridomestic triatomine-infested areas in central Brazil and fungal activity against Triatoma infestans (Klug) (Hemiptera: Reduviidae)

From 148 substrate samples collected in peridomestic triatomine-infested habitats of 24 farms in Central Brazil, 31 isolates of Metarhizium anisopliae (Metsch.) Sorok. and 15 isolates of Beauveria bassiana (Bals.) Vuill. were obtained. Most of the isolates were found in substrates that consisted of soil mixed with animal feces or soil only in areas of trees where poultry roost and pig houses. Fungi were detected with an insect bait method using Triatoma infestans (Klug), and combined in vitro and in vivo techniques with modified Chase medium and T. infestans. All isolates were highly virulent to T. infestans third instar nymphs at a relative humidity > 98% and temperature of 25 ± 0.5°C. However, activity against nymphs was reduced at 75% relative humidity. Results underline the potential of B. bassiana and M. anisopliae as agents for biological control of vectors of Chagas disease. Both species occur naturally in peridomestic habitats of triatomines in Central Brazil and may contribute to control these vectors and to reduce the risk of reinfestation of houses after eliminating domestic vector species.

Diatomaceous earth and oil enhance effectiveness of Metarhizium anisopliae against Triatoma infestans.

Entomopathogenic fungi, especially Metarhizium anisopliae, have potential for integrated control of peridomestic triatomine bugs. However, the high susceptibility of these vectors to fungal infection at elevated ambient humidities decreases in the comparatively dry conditions that often prevail in their microhabitats. A formulation adapted to this target pest that induces high and quick mortality can help to overcome these drawbacks. In the present study diatomaceous earth, which is used against pests of stored grains or as an additive to mycoinsecticides, delayed but did not reduce in vitro germination of M. anisopliae s.l. IP 46 conidia after >24h agitation without affecting viability, and did not hamper the survival of Triatoma infestans nymphs exposed to treated surfaces. The settling behavior of nymphs on a treated surface in choice tests depended on the concentration of diatomaceous earth and ambient light level. Conidia formulated with diatomaceous earth and a vegetable oil synergized the insecticidal effect of the fungus in nymphs, and quickly killed all treated insects, even at 75% relative humidity (LT(90) 8.3 days) where unformulated conidia caused only 25% mortality after a 25 days exposure. The improved performance of a combined oil and desiccant dust formulation of this Metarhizium isolate raises the likelihood for its successful mycoinsecticidal use for triatomine control and, apparently, against other domestic insect pests.

Record of Evlachovaea sp. (Hyphomycetes) on Triatoma sordida in the state of Goiás, Brazil, and its activity against Triatoma infestans (Reduviidae, Triatominae).

Abstract A fungal isolate was detected on a dead Triatoma sordida (Stål) collected in a peridomestic area in central Brazil. The fungus belongs to Evlachovaea Borisov and Tarasov, a new genus that was recently described in Russia. The isolate seems to be a third species and the second new and undescribed species from Brazil. The fungus was shown to be active against Triatoma infestans (Klug) third-instar nymphs at a humidity close to saturation. However, activity was reduced at a lower humidity (75%). Values of LC50 varied between 1.1 × 105 and 1.5 × 104 conidia/cm2 treated surface, 15 and 20 d after fungal application and incubation at humidity close to saturation. This new fungus may have a potential for biological control of peridomestic Chagas’ disease vectors during the rainy season.

Activity of Metarhizium spp. and Isaria spp. from the Central Brazilian Cerrado against Triatoma infestans nymphs

Entomopathogenic fungi attack Chagas disease vectors, and there is a need of effective isolates for development of biological control. Ten isolates of Metarhizium spp., four of Isaria cateniannulata and two of an Isaria sp., all isolated with Triatoma infestans as a bait insect from soils collected in Central Brazil, and tested under laboratory conditions were effective against third instar nymphs of T. infestans. This is the first report of pathogenicity of M. flavoviride var. pemphigi, M. robertsii and I. cateniannulata against T. infestans. M. robertsii IP 34 and I. cateniannulata IP 141 are among the most virulent fungi reported, and both have potential for integrated control of triatomine vectors.

Occurrence of invertebrate-pathogenic fungi in a Cerrado ecosystem in Central Brazil

Abstract Occurrence of invertebrate-pathogenic fungi in a protected area of the Cerrado region of Brazil is reported. Fungi were baited with triatomines, ticks, aquatic snails or mosquito larvae from substrates or collected from infected insects. The findings underscore the importance to preserve these fungi and to investigate their potential for vector control.

A new resting trap to sample fungus-infected mosquitoes, and the pathogenicity of Lecanicillium muscarium to culicid adults

Some soil-dwelling entomopathogenic fungi that are widely used in pest control are also able to reduce the survival of adult mosquito vectors under laboratory conditions. However, there is still little information about the naturally occurring fungal pathogens affecting culicid mosquitoes. As such, we hypothesized that fungi that already kill mosquitoes in realistic domestic environments could be effective against these vectors in human habitations. A simple, inexpensive, handmade, cylindrical kiln-fired clay pot (30 cm height, 24 cm inner diameter, 0.8-1cm wall thickness) was modified into a trapping device for resting adult mosquitoes and to sample fungus-infected moribund and dead individuals. The entomopathogenic fungus Lecanicillium muscarium was isolated from a dead culicid mosquito collected with this trap in southeastern Tanzania. This isolate is the first L. muscarium reported to occur naturally on adult culicids in Tanzania and was found to be pathogenic also to adults of Aedes aegypti, Anopheles arabiensis and Culex quinquefasciatus under laboratory conditions. The trapping device confirmed its efficacy to sample mosquito-specific fungi in domestic locations and that the isolated fungus might have potential for mosquito control.

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

Evlachovaea sp was tested on nymphs of 5 Triatoma spp 5 Rhodnius spp, Panstrongylus herreri and Dipetalogaster maximus at 25 degrees 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.