## 4 Discussion
anisopliae_ and _B. brongniartii_) to 24.5 (_I. farinose_) days [29]. In similar screening laboratory bioassays, three isolates (one _B. bassimana_ BbPf VRI 1198 and two _M. anisopliae_ MaPf VRI 0198 and MaPf NRCC 98) proved highly virulent on larvae of the cashew tree borer, _Ploaceterus ferrigueus_ L. (Coleoptera: Cerambycidae) causing mortality > 90% at 21 days after treatment [28]. Similar conclusions were reached when the European spruce bark beetle _Ips typographus_ ([PERSON]) (Coleoptera: Curculiidae) was treated in the laboratory with strains of _B. bassimana_ and _M. anisopliae_, where 100% mortality at four days post treatment was recorded [31]. Recently, 23 _B. bassimana_ strains were tested against adults of the Japanese pine sawyer _Monochamus alternatus_ [PERSON] (Coleoptera: Cerambycidae) and three of them showed great virulence given that all treated adults died by the 12 th day of the experiment [32]. The same fungal entomopathogen was found to be effective against both adults and eggs of _Xylotrechus basifuliginosus_ [PERSON] (Coleoptera: Cerambycidae). After 12 days of exposure under laboratory conditions, mortality was 71.34% in adults and 86% inhibition in the eggs, while in field conditions adult mortality reached 38.4% [46]. On the other hand, larvae of _Oshrranteria cerulescens_ [PERSON] (Coleoptera: Cerambycidae) were quite resistant (34% mortality) when exposed for 18 days to conidial solutions of _Cladosporium_ sp. [47]. As previously stated, the most effective method of controlling the pest would be the removal and destruction of infested dry shoots from autumn to early spring, before the emergence of adults. However, the excessive height of many hazel and walnut trees makes this practice practically impossible. Additionally, farmers may lack adequate information about this pest, making it challenging for them to differentiate between the damage caused by this pest and the natural drying process of twigs. Conversely, [PERSON] et al. [13] reported that in Sardinia, despite the evident impact of _O. linearis_ on hazel trees, the loss could be mitigated through appropriate pruning. However, this assertion does not apply to Greek walnut trees, as observed in the field. It is evident that for large-scale producers, the removal of infected branches on hundreds of hectares of trees is impractical, given the time and financial constraints involved. Although the abovementioned data cannot be directly compared with our results, as they involve different insect species, fungal strains, and experimental protocols, they are indicative of the value of EPF as biological control agents against wood-boring beetles. There are several other factors that influence the insecticidal efficacy of EPF, including the insect's behavior, population density, age, nutrition, and genetic information, as well as the host's physiology and morphology that affect its sensitivity to biological control agentslike EPF [48]. Therefore, the differences in insect susceptibility to EPF cannot be explained solely as a function of the applied conidial concentration [49]. It should also be noted that the host specificity, and especially possible lethal effects of EPF on non-target organisms, is another parameter that must be considered before the practical application of EPF in the field. It has been shown by several studies that many EPF species may have a significant negative effect on pollinators (bees, bumblebees, etc.) and entomophagous insects [50; 51; 52; 53] This obstacle can be overcome by selecting strains that are harmless to beneficial insects. It has been demonstrated that certain EPF isolates did not cause any harm to non-target insects [54]. Given the specificity of the ecological characteristics of these pests, in order to draw safe conclusions, field studies are necessary, in addition to laboratory tests, where the virulence of EPF is very likely to vary with respect to laboratory data. The results should also be useful in selecting natural fungi strains for use against this insect pest.