Evaluation of entomopathogenic fungi for the control of Tetranychus urticae (Acari: Tetranychidae) and the effect of Metarhizium brunneum on the predatory mites (Acari: Phytoseiidae)

Abstract

The efficacy of the entomopathogenic fungi (EPF), Metarhizium brunneum (strains ARSEF 4556 and V275), Metarhizium flavoviride UPH-0288, Lecanicillium lecanii UPH-0241, and Beauveria bassiana UPH-1103 against the different developmental stages of the two spotted spider mite (TSSM), Tetranychus urticae, was investigated at 1×107conidia/ml concentration in detached leaf Petri dish and whole plant pot assays. One of the most virulent strains, M. brunneum V275 (=Novozymes Met52/F52), was screened using a range of doses against adult female predatory mites, Phytoseiulus persimilis and Neoseiulus californicus. All the EPF tested killed 11.8–14.3% and 12.8–17% of the TSSM eggs in Petri dish and pot assays, respectively. They also caused 57.3–90.3% and 29.5–67.5%, mortality of the mobile stages in the Petri dish and pots trials, respectively. TSSM adults were generally more susceptible to the EPF than the juveniles. Adult mortality was >80% for all strains except M. flavoviride which caused 67% mortality. Predatory female mites were also susceptible to M. brunneum V275 with mortality being dependent on the dose and predator species; thus mortality at 1×106, 1×107 and 1×108conidia/ml was 57.5, 80.5, and 99.5% for P. persimilis and 51.5, 75.0, and 90.5% for N. californicus, respectively. However, subsequent biological stages (eggs and juveniles) were not affected by the fungal pathogen, and the number of new generation mobile stages increased 3–9-fold compared with the initial number of released predatory mites. The current study thus shows that M. brunneum V275 application with the releases of predatory mites have the potential to suppress T. urticae.