The Time–Concentration–Mortality Responses of Western Flower Thrips, Frankliniella occidentalis, to the Synergistic Interaction of Entomopathogenic Fungus Metarhizium flavoviride, Insecticides, and Diatomaceous Earth

Western flower thrips (WFT), Frankliniella occidentalis (Pergande), is a highly invasive pest which is harmful to many cash crops globally and resistant to various insecticides. Entomopathogenic fungi (EPF), as biological control agents, have demonstrated a good control effect on WFT. The aim of this study was to evaluate the synergistic and pathogenicity efficacy of the fungal strain Metarhizium flavoviride WSWL51721 when distributed with diatomaceous earth (DE) and the active ingredient imidacloprid using four bioassay methods against adult and second instar larvae of WFT. The data of the four bioassays have been fitted to the time–concentration–mortality (TCM) model. The corrected mortality ranges of WFT adults were 75–100%, 82.69–100%, 78.85–100%, and 92.31–100%, and the corrected mortality ranges of WFT second instar larvae were 72.22–100%, 85.19–100%, 77.77–100%, and 100% in the four bioassays at concentrations of 1.2 × 106 to 1.2 × 108 conidia/mL, respectively. At 1.2 × 108 conidia/mL, assays 2 (M. flavoviride with DE), 3 (M. flavoviride with imidacloprid), and 4 (M. flavoviride with DE and imidacloprid) had the shortest median lethal time (LT50), compared with that of assay 1 (M. flavoviride alone) for adults at 2.26 d, 2.06 d, and 1.53 d, and second instar larvae at 2.45 d, 1.70 d, and 1.41 d, respectively. The median lethal concentration (LC50) in the four bioassays decreased within 3–10 days of inoculation. On the third day, it was found that the lowest median lethal concentrations in assays 2, 3, and 4 were 1.58 × 107, 1.13 × 107, and 3.39 × 106 conidia/mL, respectively, which were significantly different from that in assay 1 for the adults. For the second instar larvae, assays 2, 3, and 4 also had the lowest lethal concentrations and were significantly different from those of assay 1. There were significant differences in sporulation between adults and second instar larvae under the four bioassays. Our results indicate that assays 2 (M. flavoviride with DE), 3 (M. flavoviride with imidacloprid), and 4 (M. flavoviride with DE and imidacloprid) demonstrate synergistic effects on the control of both adult and second instar larvae of WFT under laboratory conditions.

Current Knowledge of the Entomopathogenic Fungal Species Metarhizium flavoviride Sensu Lato and Its Potential in Sustainable Pest Control

Fungal entomopathogens are gaining increasing attention as alternatives to chemical control of arthropod pests, and the literature on their use under different conditions and against different species keeps expanding. Our review compiles information regarding the entomopathogenic fungal species Metarhizium flavoviride (Gams and Rozsypal 1956) (Hypocreales: Clavicipitaceae) and gives account of the natural occurrences and target arthropods that can be controlled using M. flavoviride. Taxonomic problems around M. flavoviride species sensu lato are explained. Bioassays, laboratory and field studies examining the effect of fermentation, culture regimes and formulation are compiled along with studies on the effect of the fungus on target and non-target organisms and presenting the effect of management practices on the use of the fungus. Altogether, we provide information to help conducting basic studies, and by pointing out relatively uncharted territories, help to set new research areas.

Ação de fungicidas sobre o crescimento do fungo entomopatogênico Metarhizium sp.

O uso abusivo de inseticidas químicos na agricultura pode trazer grandes prejuízos à saúde humana, ao meio ambiente e pode causar o aumento na abundância de pragas agrícolas, graças ao desequilíbrio resultante da destruição de inimigos naturais, como fungos entomopatogênicos, importantes no controle biológico de pragas agrícolas. O trabalho visa a avaliar a interferência de dois fungicidas químicos, Nativo® e Bendazol®, sob o desenvolvimento dos fungos Metarhizium anisopliae var. acridum; Metarhizium flavoviride var. flavoviride; Metarhizium anisopliae var. lepidiotum, sendo utilizados no controle biológico na cultura da soja. Os testes foram realizados in vitro, em meio de cultura BDA, na presença dos fungicidas na concentração recomendada para uso no campo em seis diluições e teste controle. Foi avaliado o efeito tóxico do fungicida por meio do crescimento vegetativo do fungo. O fungicida Nativo® apresentou CIM de 20 μL/L, para o fungo M.anisopliae var. acridum; CIM de 150 μL/L para o fungo M. flavoviride var. flavoviride; CIM de 350 μL/L, parao fungo M. anisopliae var. lepidiotum. O fungicida Bendazol® apresentou CIM de 170 μL/L para o fungo M.anisopliae var. acridum; CIM de 350 μL/L, para o fungo M. flavoviride var. flavoviride; CIM de 350 μL/L, parao fungo M. anisopliae var. lepidiotum. Dessa forma, pode-se concluir que os fungicidas Nativo® e Bendazol® inibem o crescimento das linhagens de Metarhizium sp.