B. P. Magalhães

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.

Field Trial with the Entomopathogenic Fungus Metarhizium anisopliae var. acridum against Bands of the Grasshopper Rhammatocerus schistocercoides in Brazil

The efficacy of a mycoinsecticide formulated in vegetable oil was tested in Brazil against the grasshopper Rhammatocerus schistocercoides . A set of experiments was conducted in the Chapada dos Parecis region (Mato Grosso state), a permanent zone of outbreaks for this pest. Experiments were performed in zones of natural vegetation, against grasshopper bands in the third nymphal instar. Three nymphal bands were treated with a mycoinsecticide formulation based on conidia of the entomopathogenic fungus Metarhizium anisopliae var. acridum ( =M. flavoviride ), strain CG 423. Three non-treated bands were used as control. The application was made with the aid of a hand-held ULV sprayer adjusted to deliver 2 l of the formulation ha -1 , each containing 1 2 10 13 conidia. Treatments were limited to the surface of the grasshopper bands and their immediate borders (5-10 m). The efficacy of the mycoinsecticide was evaluated through band survival after treatment (grasshopper numbers, surface, density, behaviour and daily movement of the band), allowing the insects to move freely in their natural environment. Insects were regularly surveyed and maintained in the laboratory, allowing estimates of the infection rate. Field and laboratory studies showed a clear effect of the product 10 days after treatment. At 14 days post-spraying, mortality caused by the mycoinsecticide in the field was approximately 88%.

Description of a Zoophthora radicans (Zygomycetes: Entomophthoraceae) epizootic in a population of Empoasca kraemeri (Homoptera: Cicadellidae) on beans in central Brazil

Development of a natural epizootic of Zoophthora radicans in an Empoasca kraemeri population on beans near Goiânia, Goias, Brazil, was monitored over a 6-week period. At the initiation of monitoring on 23 April 1985, disease prevalence in the leafhopper population was 12.8%. Over the course of the epizootic, infection of second-, third-, fourth-, and fifth-instar nymphs was similar and reached a peak of approximately 55% on 13 May, while infection of adult leafhoppers never exceeded 19%. Fungal inoculum expressed as the number of host cadavers with active (sporulating) fungus attached to the bean foliage was the variable most closely correlated to disease prevalence. Variables quantifying moisture or moisture combined with temperature (degree hours under moist conditions) were the most important abiotic predictors. A moisture variable incorporating a quantitative measure of moisture (level of wetness of a leaf wetness sensor) and a variable based only on the presence or absence of free moisture (dew) were equivalent predictors of disease prevalence. Epizootic development appeared to be inhibited when foliage was wet for less than 9 hr during the night. Infection trends in relation to fungus inoculum levels indicated an inoculum density threshold for epizootic development of approximately 0.8 leafhopper cadavers per plant.

The use of Metarhizium anisopliae var. acridum against the grasshopper Rhammatocerus schistocercoides in Brazil

Abstract The control of grasshoppers in Brazil has been based exclusively on chemical insecticides (fenitrothion and malathion). However, as these products are known to be harmful to the environment, their massive use has caused concerns. In the face of pressure against their use, the development of alternative methods became imperative. Some species of entomopathogenic fungi can supplement or even replace chemical insecticides in the control of grasshoppers. An integrated research project began in Brazil in 1993 with the specific objective of developing bioinsecticides based on entomopathogenic microorganisms, especially fungi, to control grasshoppers. Activities centered in surveys, characterization, production, formulation, and field evaluation. Emphasis was given to developing the fungus Metarhizium anisopliae var. acridum as the most promising biocontrol candidate. It is now known that this pathogen can be used efficiently in the control of Rhammatocerus schistocercoides in Brazil and we are verifying its effects on non-target organisms, including other Orthoptera, Diptera and Hymenoptera.

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

O fungo Beauveria bassiana (Bals.) Vuill., isolado CG 306, foi testado contra o Triatoma infestans (Klug) atraves de aplicacao indireta por contato do inseto com papel filtro tratado com conidios. O patogeno foi aplicado sobre papel filtro atraves de filtragem a vacuo de uma suspensao de conidios. Foram feitas estimativas do tempo medio de sobrevivencia entre 15 e 21 dias nas densidades de 3x106 e 107 conidios/cm2, respectivamente, sem diferencas significativas entre as concentracoes. A concentracao de 2,4x106 conidios/cm2 de CG 306 foi necessaria para matar 50% de ninfas de terceiro instar de T. infestans 25 dias apos inoculacao e incubacao a 25°C e 50% de umidade relativa. A CL50 foi estatisticamente maior (2,0x107 conidios/cm2) quando os insetos foram expostos por uma hora aos conidios distribuidos sobre papel filtro. Um emulsificante a base de oleo mineral (2%) nao afetou a germinacao de conidios in vitro. Um numero menor de conidios foi necessario para matar 50% dos insetos apos exposicao constante ao papel filtro tratado, em comparacao com os conidios nao formulados com o emulsificante. Quando a exposicao foi limitada a 1 h, os conidios nao formulados foram mais efetivos do que conidios formulados. Apos aplicacao de B. bassiana (107 conidios/cm2) em pequenas casas experimentais de madeira, seguida de liberacao de ninfas de terceiro instar de T. infestans, o nivel de infeccao de insetos recuperados 25 dias apos aplicacao com o fungo foi significativamente inferior as encontrado na casa-testemunha. A mortalidade atribuida a infeccao fungica de insetos recuperados e mantidos em laboratorio foi de 38,1 a 93,8%. A mortalidade de insetos expostos ao papel filtro tratado e mantido em copos cobertos com gaze dentro das casas, foi de 35 a 78,8% 25 dias apos aplicacao. A persistencia dos conidios foi superior a 98% durante os experimentos de campo. Nao houve desenvolvimento de B. bassiana sobre cadaveres originados de infeccao provocada em laboratorio e posteriormente expostos as condicoes de campo no interior das casas.

Food consumption of Rhammatocerus schistocercoides Rehn (Orthoptera: Acrididae) infected by the fungus Metarhizium flavoviride Gams & Rozsypal

Foliage consumption by nymphs and adults of the grasshopper Rhammatocerus schistocercoides Rehn infected with the fungus Metarhizium flavoviride Gams & Rozsypal was evaluated. Sixth and eighth instar nymphs and female adults consumed on average (±SEM) 6.9 ± 0.36 cm2 (60.7 ± 2.92 mg of dry matter), 11.0 ± 1.35 cm2 (74.9 ± 9.24 mg d.m.), and 16.0 ± 0.50 cm2 (126.5 ± 6.35 mg d.m.) of sugarcane leaves per day, equivalent to 85.4, 35.9 and 41.9% of the insect body weights, respectively. Eighth instar nymphs and female adults inoculated with M. flavoviride (5,000 conidia / insect) ingested less food from day three onward and showed at day 10 an average consumption 74.5 and 45.6% lower than control insects, respectively. Adult females topically treated with a sub-lethal dosage (3 ml of a 8 ppm suspension / insect) of the chemical insecticide diflubenzuron showed consumption rates comparable to untreated insects (P=0.065). The combination fungus + chemical did not show results different from those obtained with the fungus alone (P=0.405). A strong correlation (r2=0.998) between production of fecal pellets by R. schistocercoides and food consumption was observed. These results confirmed the high voracity of R. schistocercoides and showed a remarkable adverse effect of the fungus on food intake by infected nymphs and adults.

Polymorphism of the grasshopper Schistocerca pallens (Thunberg) (Orthoptera: Acrididae) and its natural pathogen Metarhizium flavoviride Gams & Rozsypal (Hyphomycetes), revealed by RAPD analysis

The genetic variability of 27 individuals from two distinct populations (Northeast and Central Brazil) of the grasshopper Schistocerca pallens (Thunberg) and eight isolates of its natural pathogen, the fungus Metarhizium flavoviride Gams & Rozsypal, was investigated using RAPD analysis. For the grasshoppers, ten different 10-mer oligonucleotide primers of arbitrary sequence were selected for analysis, resulting in 79 scorable binary characters. The program RAPDDIP applied to S. pallens revealed nucleotide diversity of 2.3 and 2.2% for the populations from Rio Grande do Norte (Northeast Brazil) and Federal District (Central Brazil), respectively. These values indicate the presence of high genetic variability within these populations. Conversely, the value for nucleotide divergence (0.004) showed almost no distinction between the two populations. In the case of M. flavoviride, thirty-one 10-mer oligonucleotide primers of arbitrary sequence were selected for analysis, producing 388 scorable binary characters. A dendrogram obtained for M. flavoviride, using the program NTSYS, revealed high homogeneity (similarity ≥79.5%) among the 8 isolates analyzed. The Brazilian isolates, all from the same geographical area and host (S. pallens), were even more homogeneous (≥98.3%).

Effect of two dosages of Metarhizium anisopliae var. acridum against Rhammatocerus schistocercoides Rehn (1)

The fungus Metarhizium anisopliae var. acridum, strain CG 423, was tested under field conditions against the gregarious grasshopper Rhammatocerus schistocercoides (Rehn) (Orthoptera: Acrididae). Conidia formulated in a racemic mixture of soybean oil and kerosene were sprayed under field conditions using an ultralow-volume hand-held atomizer Ulva Plus adjusted to deliver 2.9 L/ha. Bands composed of 2 nd instar nymphs were treated with either 5.0x10 12 or 1.0x10 13 viable conidia/ha. The number of insects in each band was estimated at day one following spraying and by the end of the field trial (15 to 16 days post- treatment). Reductions in population size reached, in average, 65.8% and 80.4% for bands treated with the higher and lower dosage, respectively. For both dosages, total mortality rates of insects collected at two days post-application, and kept in cages for 14 days under lab conditions, showed no significant differences as compared to that obtained with insects collected immediately after spraying. Healthy insects were fed to native grasses sprayed on the field with 1.0x10 13 viable conidia/ha. Mortality levels of the nymphs fed on grasses collected two and four days post-application were not affected when compared to nymphs fed on grasses collected immediately following application.

Sporulation of Metarhizium anisopliae var. Acridum and Beauveria bassiana on Rhammatocerus schistocercoides under humid and dry conditions

The sporulation of the fungi Metarhizium anisopliae var. acridum and Beauveria bassiana in cadavers of the grasshopper Rhammatocerus schistocercoides was studied in dry and humid environments. Both fungi were equally virulent against R. schistocercoides. However, internally, M. anisopliae produced more conidia than B. bassiana at 53% and 75% relative humidity. Externally, there was no sporulation at 53% and 75% RH, and M. anisopliae produced more conidia than B. bassiana at 100% RH.

Differentiation of the entomopathogenic fungus Metarhizium flavoviride (Hyphomycetes)

A diferenciacao de um isolado brasileiro de Metarhizium flavoviride (CG 423), candidato a agente de controle biologico de gafanhotos, foi investigada. Conidios semeados em meio de cultura solido (extrato de levedura 1%, agar 2,8%, agua destilada 96,2%) e incubados a 28°C, foram observados durante 26 horas. Para induzir a formacao de apressorios, conidios foram suspensos em meio liquido contendo duas concentracoes de extrato de levedura (0,06 e 1%) e transferidos para placas de Petri plasticas (3,5 cm de diâmetro). A germinacao teve inicio com o aumento do tamanho dos conidios de 5,3 ± 0,6 x 3,1 ± 0,3 µm (0 h de incubacao) para 8,1 ± 0,2 x 6,1 ± 0,2 µm (8 h de incubacao). Os primeiros tubos germinativos comecaram a surgir apos 10 h de incubacao dos conidios, os quais apresentaram acentuada multipolaridade. Vinte e seis horas apos a inoculacao foi observado o inicio da diferenciacao micelial e formacao de anastomoses entre hifas de conidios adjacentes. Apressorios foram formados somente quando conidos foram incubados em meio liquido contendo concentracao minima de nutriente (extrato de levedura 0,0%; peso/volume). Os apressorios formados encontravam-se fortemente aderidos a superficie do fundo plastico da placa de Petri.