Susceptibility of Oligonychus yothersi (Acari: Tetranychidae) to the fungus Beauveria bassiana

Abstract

The Paraguay tea (Ilex paraguariensis) crop is an important economical activity in Southern Brazil. With the increase of tea consumption in the 80s, the number of monoculture crops also increased, creating favorable conditions for the development of phytophagous insect and mite populations, such as the red mite Oligonychus yothersi. The objective of this study was to evaluate the susceptibility of the red mite O. yothersi to the several strains of the Beauveria bassiana fungus. The experiments were carried out in Cascavel, PR, Brazil. Leaf disks of Paraguay tea (2.2 cm²) were previously infested with 20 adult females. Five disks were inoculated with 1 mL of each conidial suspension of B. bassiana strains (1x10(8) conidia per mL). Disks were kept afloat on distilled water in plastic boxes (3 cm diameter), under controlled conditions. Dead mites were transferred to a humid chamber on a daily basis to confirm the mortalities rate by the fungus. All the strains were pathogenic, with total mortality varying from 77 to 98%, 6 days after application. It was not possible to differentiate virulence levels between strains (P<0.05) by total mortality. However, confirmed mortality varied from 19 to 75%, 8 days after application, allowing for a differentiation in virulence levels between strains (P<0.05). This study concluded that the O. yothersi red mite is susceptible, at different levels, to B. bassiana tested strains.