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

Abstract

Rhammatocerus schistocercoides is a serious pest of several crops and native pastures in Mato Grosso State, Brazil (8). The reduction or replacement of chemical insecticides by mycoinsecticides to control this insect is under investigation (5,6). Metarhizium anisopliae var. acridum (= M. flavoviride; 1) is very infective to R. schistocercoides (6, 10), and Beauveria bassiana to Melanoplus sanguinipes (3). During previous research at Embrapa Genetic Resources and Biotechnology it was noted that M. anisopliae var. acridum sporulated profusely within dried cadavers of R. schistocercoides (10). We report here on a laboratory experiment devised to compare internal and external sporulation of M. anisopliae var. acridum and B. bassiana on R. schistocercoides cadavers kept in humid and dry conditions.Insects. Insects used in this study were collected in the field (Silvânia, GO, Brazil) and maintained in 60 cm x 60 cm x 80 cm cages in the laboratory at 25°C and 12h photophase. They were fed sugar cane leaves, oats and wheat germ during 15 days before testing, without regard to gender.Fungal isolates and culture. Isolates CG 423 (M. anisopliae var. acridum) and CG 425 (B. bassiana) were provided by Embrapa Genetic Resources and Biotechnology, Collection of Entomopathogenic Fungi, Brasília, DF. The isolate CG 423 was first found infecting the pallid grasshopper Schistocerca pallens in Rio Grande do Norte State (7), and the isolate CG 425 infecting R. schistocercoides in Mato Grosso (5). The fungi were cultured in SDAY (1% neopeptone, 2% dextrose, 1.5% agar, and 1% yeast extract, completed to 1000 ml distilled water, ph calibrated to 6.2) after retrieval from storage in liquid nitrogen. For the bioassay, the fungi were culture in rice as described by Magalhães and Frazão (4).Bioassay. Groups of 30 R. schistocercoides adults were tested with either M. anisopliae var. acridum (CG 423) or B. bassiana (CG 425). To perform the bioassays, insects were individually inoculated with 3 µl of a conidial suspension (5000 conidia/insect) applied on the right pleural region with a micropipette. Insects were maintained in 17 cm x 21 cm x 25 cm cages (10/cage) at 25°C and 12 photophase and were fed sugar cane leaves, oats and wheat germ. Dead adults were removed daily. One femur was dissected from each insect and a drop of hemolymph was extracted and observed under the microscope for presence of blastospores. SPORULATION OF METARHIZIUM ANISOPLIAE ABSTRACTThe 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.

Cuticle-degrading proteases produced by the entomopathogenic fungus Beauveria bassiana in the presence ofcoffee berry borer cuticle

“…Furthermore, this strain showed compatibility with chemical insecticides used in the coffee crop, allowing the development of an integrated pest management program strategy for the crop with reduction in the amount of insecticides applied (21). This fungal strain also presented high mortality against the grasshopper Rhammatocerus schistocercoides (20) which is a serious pest of crops and native pastures in Central Brazil.…”

Comportamento E Aspectos Citológicos De Beauveria Basssiana Após Passagem Em Ovo, Larva E Adulto De Chrysomya Albiceps

“…A rápida esporulação pode ser um importante critério para seleção de isolados fúngicos, pois auxilia na propagação de epizootias, além de ser uma vantagem em relação às defesas humorais de insetos (MITCHELL, 2003). Contudo, os fatores abióticos (como a temperatura e a umidade) podem alterar a esporulação (LUZ et al, 1998;ALVES, 1998;MAGALHÃES, 2000). O crescimento radial também é empregado para avaliar linhagens quanto à virulência, pois, de acordo com HAEJEK; ST LEGER (1994),,,,, a taxa de crescimento radial está diretamente associada à velocidade de infecção no hospedeiro.…”