USE OF METARHIZIUM-FLAVOVIRIDE FOR CONTROL OF ZONOCERUS-VARIEGATUS - A MODEL, LINKING DISPERSAL AND SECONDARY INFECTION FROM THE SPRAY RESIDUE WITH MORTALITY IN CAGED FIELD SAMPLES

A field trial was conducted using an oil formulation of the entomopath ogenic fungus. Metarhizium flavoviride Gams & Rozsypal (Deuteromycotin a: Hyphomycetes), to control the variegated grasshopper: Zonocerus var iegatus L. (Orthoptera: Pyrgomorphidae). The influence of dispersal an d secondary pick-up from the spray residue on mortality was assessed b y sampling insects from the treated plots at intervals and monitoring disease levels during subsequent incubation in the laboratory. The cum ulative mortality curves showed the pathogen to be highly effective, e ven in samples taken 8 days after spraying. A model was developed to l ink the influence of mortality, incubation, secondary pick-up of spore s and insect dispersal, on the shape of these cumulative mortality cur ves. The model proved useful for data received from an experiment usin g small plot sizes, where insect dispersal is a big problem. The spray residue had an important influence on overall insect mortality. The m odel also indicated a difference in speed of kill between field and la boratory samples, suggesting an incubation delay in the field.