Biology Reference
In-Depth Information
5.1.1
Beauveria
and
Metarhizium
production of conidia in clusters to give a white
appearance on sporulating cadavers, thus
giving it its common name 'white muscardine'
(Samson
et al.
, 1988) (Fig. 5.1).
Members of this group used for insect
control are either
Beauveria bassiana
or
Beauveria
brongniartii. B. bassiana
is a generalist fungus,
with a known host range of about 700 arthropod
species. The pathogen is able to infect both
immature and adult stages of all groups of
insects. It has a cosmopolitan distribution, is
found naturally in the soil and is a common
pathogen of many ground-dwelling insects such
as beetle larvae (Lacey
et al.
, 1999). It is ef ective
against Culicidae (mosquitoes), Acarina (ticks),
Muscidae (fl ies),
Reduviidae (predatory bugs)
and Phlebotominae (sandfl ies). Using sequences
of 86 isolates from around the world, the group
Beauveria
was shown to comprise six clades (A to
F) (Rehner and Buckley, 2005) with
B. bassiana
being non-monophyletic and falling both into
clades A and C with little host specifi city. A
particularly large number of isolates from clade
A have been registered as commercial strains.
Beauveria bassiana
is used as an insecticide of
household and agricultural pests in bait traps,
aerial, foliar or substrate spray treatments using
wettable powders or formulated suspensions
Beauveria
spp. and
Metarhizium
spp. are part of
the artifi cial group of Hyphomycete fungi,
which were thought to be without sexual stages.
Among entomopathogenic fungi, Hyphomycetes
have the most diverse host ranges (Goettel and
Inglis, 1997). Due to their ease of production,
the greatest advances in fungal control of
vectors have been made using
Beauveria
spp.
and
Metarhizium
spp. Since their classifi cation as
Hyphomycetes, their sexual forms have been
identifi ed, and they have therefore been re-
classifi ed as Ascomycetes. These fungi are
fi lamentous spore-producing fungi that grow as
a mat of mycelia on a substrate.
Beauveria
Beauveria
was identifi ed by the Italian scientist
Agostino Bassi in 1835, who was also the fi rst
person to demonstrate that microbes can be
pathogens of animals. However, accounts as
early as AD900 from Japan describe 'muscardine'
silkworms (Steinhaus, 1975), and
Beauveria
was
considered to be the causative agent of severe
losses of silkworm larvae in the 16th and 17th
centuries. These fungi are characterized by the
Fig. 5.1.
Cadaver of
Anopheles stephensi
female mosquito sporulating with
Beauveria bassiana
.
(Photo
courtesy of Jennifer Stevenson.)
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