| Summary: | Five isolates of <i>Metarhizium</i> sp. were evaluated for their pathogenicity against the spider mite (<i>Tetranychus truncatus</i> Ehara) (Acari: Tetranychidae) and <i>Metarhizium</i> sp. BCC 4849 resulted in the highest mortality (82%) on the 5th day post-inoculation (DPI). Subsequent insect bioassay data indicated similar high virulence against five other insects: African red mites (<i>Eutetranychus africanus</i> Tucker) (Acari: Tetranychidae), bean aphid (<i>Aphis craccivora</i> Koch) (Hemiptera: Aphididae), cassava mealybug (<i>Phenacoccus manihoti</i> Matile-Ferrero) (Hemiptera: Pseudococcidae), sweet potato weevil (<i>Cylas formicarius</i> Fabricius) (Coleoptera: Brentidae), and oriental fruit fly (<i>Bactrocera dorsalis</i> Hendel) (Diptera: Tephritidae), at mortalities of 92–99%, on 3rd–6th DPI, and in laboratory conditions. The pathogenicity assay against <i>E. africanus</i> in hemp plants under greenhouse conditions indicated 85–100% insect mortality on 10th DPI using the fungus alone or in combination with synthetic acaricide. Genome sequencing of <i>Metarhizium</i> sp. BCC 4849 revealed the high abundance of proteins associated with zinc-, heme-, and iron-binding; oxidation-reduction; and transmembrane transport, implicating its versatile mode of interaction with the environment and adaptation to various ion homeostasis. The light and scanning electron microscopy indicated that at 24 h post inoculation (PI), adhesion and appressorial formation occurred, notably near the setae. Most infected mites had stopped moving and started dying by 48–72 h PI. Elongated hyphal bodies and oval blastospores were detected in the legs. At 96–120 h PI or longer, dense mycelia and conidial mass had colonized the interior and exterior of dead mites, primarily at the bottom than the upper part. The shelf-life study also indicated that conidial formulation combined with an oxygen-moisture absorber markedly enhanced the viability and germination after storage at 35 °C for four months. The fungus was tested as safe for humans and animals, according to our toxicological assays.
|
|---|