Efficacy of oil-based formulations of Metarhizium anisopliae and Beauveria bassiana against Tibraca limbativentris in flooded rice

The fungus Metarhizium anisopliae (Hypocreales: Clavicipitaceae) (Ma) causes natural epizootics to the rice stalk stink bug Tibraca limbativentris in Brazil. We evaluated the effectiveness of oil-based formulations of M. anisopliae in a flooded rice (cv. Jaçanã) paddy in Goianira, GO, Brazil. Treatments were represented by two isolates of Ma (CG168 and ESALQ1037) and one of Beauveria bassiana  (Hypocreales: Cordycipitaceae) (Bb, strain ESALQ-PL63) applied at two label rates (5x10¹² and 1x10¹³ viable conidia/ha) using emulsifiable oil (sunflower) formulations. Treatments were sprayed on rice plants previously infested with 40 adult bugs confined in screened cages (1 m²) arranged in five randomized blocks. Fungal preparations were sprayed using a backpack sprayer with two flat nozzles at 200 L/ha. Insect mortality was evaluated over three weeks. Estimates of conidia deposition at lower and higher label rates were 1.8±0.3 and 5.3±0.9x10⁴ conidia/cm² for Ma and 2.5±0 and 6.4±0.4x10⁴ conidia/cm² for Bb, respectively. Insect counts revealed that Ma strains CG168 and ESALQ1037 both applied at 1x10¹³ conidia/ha provided 43-46% and 28-30% mortality of adult stink bugs in the field 12 and 19 days post-application, respectively. Furthermore, both Ma strains reduced incidence of dead heart but grain yield was not affected by any fungal treatment. Bb treatments were not effective. Adults collected from Ma field cages died more quickly compared with those from Bb-treated cages, regardless of the concentration applied. Our results indicated that oil-based formulation of Ma-CG168 can be used as a component of integrated stalk stink bug management in rice.