| Popis: |
Entomopathogenic fungi and predatory mites can independently contribute to control the two-spotted spider mite Tetranychus urticae Koch. It is important to assess the risk of possible fungal infections in predators when a combination of them are being considered as a tandem control strategy for T. urticae in IPM program.The first part of this study tested 4 Beauveria bassiana isolates and 2 Metarhizium anisopliae for virulence against T. urticae, egg and adult stages. Strains B4 was found to be the most potent toward egg and adult stages, causing 88.5% mortality for the adult stage at a concentration of 108 spores/ml. and the LC50 was 6.61x 106. When applied on the egg stage the hatchability was 25.2% compared with the control which reached 99% and the LC50 was 1.14 x107. The second part evaluated the pathogenicity of the most effective isolates B4, three concentrations were applied LC25, LC50 and LC90 against the adult of the two predator mites Phytoseiulus persimilis and Neoseiulus californicus. The bioassay results indicated that the isolate B4 was harmless against P. persimilis and slightly harmful against N. californicus. No viable fungal hyphae were found on predator cadavers. Observations with scanning electron microscopy revealed that conidia were attached to the cuticle of predatory mites within 24 h after spraying with strain B4, and had germinated within 24–48 h. After 48 h, conidia had gradually been shed from the mites, after none of the conidia had penetrated the cuticular surfaces. In contrast, the germinated conidia successfully penetrated the cuticle of T. urticae, and within 72 h the fungus colonized the mite’s body. Our study demonstrated that although several B. bassiana strains displayed a high virulence in T. urticae there was no evident pathogenicity to phytoseiid mites. These findings support the potential use of entomopathogenic fungus in combination with predatory mites in T. urticae control programs. |
