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 1 of the formulation ha', each containing 1 x 10¹³ conidia. Treatments were limited to the surface of the grasshopper hands 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%. (Résumé d'auteur