Entomopathogenic fungi as promising biocontrol agents for the rosaceous longhorn beetle, Osphranteria coerulescens

During a survey for natural enemies of the rosaceous longhorn beetle (RLHB), Osphranteria coerulescens, two isolates of entomopathogenic fungi (EPF) were found in Razavi Khorasan province of Iran. These isolates were determined to be of the species Beauveria bassiana and Metarhizium anisopliae using morphological characteristics and molecular analysis. Subsequently, the mycosis process of the isolates on larvae of RLHB was documented using scanning electron microscopy (SEM). In order to assess virulence of these indigenous isolates of EPF, a series of trials were conducted against RLHB larvae, pupae and adult stages. In laboratory bioassays the pest was susceptible to both EPF isolates, but the B. bassiana isolate caused significantly higher mortality than the M. anisopliae isolate in all life stages tested. In a semi-field trial EPF suspension containing 2.5 × 10¹⁰ viable conidia per ml was sprayed directly against pest larvae beneath tree bark under two conditions: apricot branches covered with a polyvinyl cover and without cover. The B. bassiana isolate showed a higher infection rate than M. anisopliae and the cover had significant effect on larval mortality, ranging from 67 % for covered infested apricot branches to 31 % without cover in the B. bassiana treatments. Our findings revealed that polyvinyl covers were necessary to improve conidial persistence under field conditions. In a supplementary survey on the semi-mass production potential of the fungal conidia, the ability of B. bassiana and M. anisopliae to germinate was studied using three solid media. Sugar beet pulp provided the highest yield of conidia for both EPF species, and can be considered as an effective solid medium for fungal growth. These findings highlighted the potential of EPFs as biocontrol agents of O. coerulescens.