Viruses as Biological Control Agents of the Dutch Elm Disease Fungus Ophiostoma novo-ulmi

Abstract

Dutch elm disease (DED) is not a three organism “elm-fungus-bark beetle” system, as originally believed. The DED fungus, Ophiostoma novo-ulmi, also often carries with it its own natural enemy, a type of virus known as a “d-factor.” These viruses are probably specific to the fungus. DED is therefore really an “elm-fungus-fungal virus-bark beetle” system. A virus can sometimes so severely debilitate the O. novo-ulmi fungus that it critically reduces its effectiveness as an elm pathogen, preventing it from entering the sapstream of elm trees via the feeding wounds of the elm bark beetles. Indeed in some situations, the viruses may exert a strong natural biological control over the O. novo-ulmi population. Their properties are therefore being studied under field conditions and in the laboratory with a view to their possible release either as natural or genetically modified biological control agents. Washington DC, Oregon, and New Zealand appear particularly favorable target areas for experimental release of natural viruses.