ENTOMOGENOUS FUNGI
Entomogenous means ‘growing on or in the
bodies of insects’ and strictly-speaking applies to all those organisms
including bacteria and fungi. However, the word is most often used to describe
filamentous fungi that invade their insect hosts by penetrating directly
through the cuticle.
Many common and
important entomogenous fungi belong to the order Hypocreales of the Ascomycota
– Beauveria, Isaria, Hirsutella,
Metarhizium, Nomuraea, Cordyceps; and of the order Entomophthorales of the
Zygomycota - Entomophthora, Zoophthora, Pandora, Entomophaga.
LIFE CYCLE
These fungi
usually attach to the external body surface of insects in the form of
microscopic spores (usually asexual, mitosporic spores also
called conidia). Under the right conditions of temperature and (usually
high) humidity, these spores germinate, grow as hyphae and
colonize the insect's cuticle; which they bore through by way of enzymatic
hydrolysis reaching the insects' body cavity (hemocoel). Then, the
fungal cells proliferate in the host body cavity, usually as walled hyphae or
in the form of wall-less protoplasts (depending on the fungus
involved). After some time the insect is usually killed (sometimes by
fungal toxins) and new propagules (spores) are formed in or on the insect
if environmental conditions are again favourable. High humidity is usually
required for sporulation.
IMPORTANCE
Since they are considered natural mortality agents and
environmentally safe, there is worldwide interest in the use and manipulation
of entomopathogenic fungi for biological control of insects and other
arthropod pests. In particular the asexual phases of Ascomycota (Beauveria,
Isaria, Hirsutella, Metarhizium, Nomuraea, etc,.) are under intense scrutiny due to the traits
favouring their use as biological insecticides.
The Entomophthorales are often reported as causing high
levels of mortality (epizootics) in nature. These fungi are highly virulent.
The anamorphic Ascomycota (Metarhizium, Beauveria, etc.) are reported as
causing epizootics less frequently in nature.
*************
Comments
Post a Comment