Entomopathogenic Fungi as Endophytes:Plant-Endophyte-Herbivore Interactions and Prospects for Use in Biological Control

It is now evident that entomopathogenic fungi are able to colonize plant tissues as symptomless endophytes. Although most data so far published in this regard refer to Beauveria bassiana as an endophytic fungus, two other entomopathogenic fungi, viz. Metarhizium anisopliae and Lecanicillium lecanii have also been shown to colonize plant tissues endophytically. Several recent studies have also shown reasonable detrimental effects on herbivorous insects feeding on plants harbouring these fungi as endophytes. However, data published so far are highly variable and not consistent with regard to the underlying mechanisms which would allow explaining these effects. Growth conditions, specific cultivar features, or interactions with other microorganisms may impact the effect of these endophytic entomopathogenic fungi on the herbivorous insects. Furthermore, other fungi may block the systemic growth of the fungi in plant parts distant to the point of inoculation. Other parameters which need to be taken into account for using these fungi as biocontrol agents are the level of mycotoxins produced in plants, the level of pest reduction and the nature of formulations allowing a consistent colonization of the crop plants. This review discusses these and other problems related to the use of entomopathogenic fungi as endophytic biocontrol agents.