João Batista Tavares da Silva

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.

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.

Isolados de Dicyma pulvinata em estromas de Microcyclus ulei em seringueira

Dicyma pulvinata is an efficient biocontrol agent of Microcyclus ulei, causal agent of South American leaf blight. The objective of this work was to obtain strongly antagonistic isolates. A survey was carried out in rubber plantations located in 14 municipalities in the Sates of Acre, Amazonas, Bahia, Mato Grosso, Para and Roraima, Brazil, obtaining 52 isolates of D. pulvinata. The antagonistic fungus was isolated on potato-dextrose-agar (PDA) plates and identified based on morphological characteristics of conidiophores and conidia, and colony appearance. The antagonic effect was tested by inoculating D. pulvinata on Fusicladium macrosporum lesions induced on rubber plants, previously. In order to maintain the morphological and pathogenic traits, fungus isolates were preserved by lyophilization, deep freeze (-80oC) and cryogeny. All isolates were introduced into Embrapa Recursos Geneticos e Biotecnologia fungus collection.

Ação antagônica e de metabólitos bioativos de Trichoderma spp. contra os patógenos Sclerotium rolfsii e Verticillium dahliae

The antagonistic effect shown by fungi of the genus Trichoderma was assessed against the plant pathogens Sclerotium rolfsii and Verticillium dahlia, isolated from ornamental aster and strawberry, respectively. Twenty isolates of the antagonist were employed; they belonged to the species T. asperellum, T. hamatum, T. harzianum, T. koningiopsis, T. spirale and Trichoderma sp. Antagonism was investigated by means of dual culture tests and bioactive metabolite production based on the overlapping plate method. Most selected isolates had an inhibitory effect on the mycelial growth of S. rolfsii and V. dahlia, compared to controls. Except for non-volatile metabolite production tests, inhibitory action against V. dahliae was highest. Even the thermostable non-volatile metabolites showed inhibitory effect against both tested pathogens, evidencing that the secondary metabolites of the antagonist have a significant effect on these pathogenic species.

New isolates of Trichoderma antagonistic to Sclerotinia sclerotiorum

Forty-nine isolates of Trichoderma from the Brazilian Midwest were evaluated for their antagonistic activity in vitro against Sclerotinia sclerotiorum (causal agent of white mold), which were then identified based on their nuclear ribosomal ITS sequences. Paired culture tests showed that all isolates exhibited some antagonism, with a maximum of 77% mycelial inhibition and complete inhibition of sclerotia production. Two isolates were found to be the most promising biocontrol agents, considering both antagonistic parameters (CEN1253 - T. koningiopsis and CEN1265 - T. brevicompactum). Five different species were identified: T. harzianum (23), T. spirale (9), T. koningiopsis (8), T. brevicompactum (7) and T. asperellum (2). These isolates are stored in the Embrapa Fungi Collection for Biological Control and the information obtained in the experiments will be incorporated into the database of biological assets within the genetic resources information system (Allele) and be made available for further studies.

Polymorphism of the grasshopper Rhammatocerus schistocercoides populations revealed by RAPD

(2) Abstract - The objective of this work was to study the genetic variabil- ity of the grasshopper Rhammatocerus schistocercoides (Orthoptera: Acrididae) using RAPD analysis among individuals from three popula- tions, one from Colombia and two from Brazil (Goias and Mato Grosso States). Ninety scorable binary markers were obtained by fingerprinting with 11 oligonucleotide primers. Most of the polymorphism was attrib- uted to 42 markers with variable frequency among the different popula- tions. Although the existence of significant difference among popula- tions (P<0.0001), most of the genetic variability was found within popu- lations (87.7% of total variation). Pairwise distances between Colom- bian and Brazilian populations were 0.12 (P<0.0001) and 0.18 (P<0.0001) for Goias and Mato Grosso, respectively. The pairwise distance be- tween Goias and Mato Grosso populations was 0.06 (P<0.0001). These data indicated that the phenotypic differences among populations are associated mainly with the geographical distances between the Brazilian and Colombian populations.