discussed here (Asellariales, Basidiobolales,
Dimargaritales, Endogonales, Entomophthor-
ales, Kickxellales, Mortierellales, Mucorales,
Neozygitales, and Zoopagales). Based on phylo-
genetic analysis, these orders are distributed in
one phylum, Entomophthoromycota, and four
subphyla, Kickxellomycotina, Mortierellomy-
cotina, Mucoromycotina, and Zoopagomyco-
tina (Hibbett et al. 2007 ; Hoffmann et al. 2011 ;
Humber2012b) (Table8.1).
C. Phylum Entomophthoromycota (Fig.8.1)
The members of Entomophthoromycota are
saprobes or arthopod pathogens that form
simple or branched conidiophores, each of
which apically produces a single primary con-
idium. Primary conidia are composed of wall
layers that are continuous with those of the
conidiophore and are usually forcibly dis-
charged; if they land on an unfavorable sub-
strate, then a secondary conidium can be
produced. Secondary conidia can be actively
or passively discharged and may or may not
have the same shape as the primary conidium.
Resting spores have a two-layered, relatively
thick wall, and each contains two to many
nuclei. Resting spores can be formed as a
result of conjugation (zygospore) or without
conjugation (azygospore). Arthropod patho-
gens may produce rhizoids that may or may
not possess holdfasts to attach the infected
host to the substrate and cystidia to break the
host cuticle to facilitate conidiophore emer-
gence.
- Morphology
a) Vegetative Structures
The vegetative structures of most pathogenic
taxa in Entomophthoromycota are short seg-
ments (hyphal bodies), whereas coenocytic to
sparingly septate hyphae are more character-
istic of saprobic taxa in this phylum.Multinu-
cleate hyphal bodies may be walled or, in many
entomopathogens, wall-less protoplasts whose
morphology may rapidly change in shape but
are generally fusoid or in highly irregular (or
even beadlike) filaments with prominent filo-
podia (Tyrrell 1977 ; Macleod et al. 1980 ) that
are immobile and hyphoid (Butt et al. 1981 ).
Septate hyphae with uninucleate cells occur
only inBasidiobolus.b) Asexual Spores (Conidia)
Entomophthoralean conidia [Fig.8.1(5–8)] are
covered by the same outer electron-dense and
inner electron-lucent wall layers covering the
conidiogenous cell [Fig.8.1(4)]. The spores are
cut off by a centripetal infolding of the inner
(electron-lucent) wall layer, resulting in a
bilayered septum composed of two electron-
lucent layers; no new internal (sporangios-
pore) wall is formed at any time during spore
formation(Benny et al. 2001 ). Conidial dis-
charge occurs when the outer (electron-dense)
layer breaks at the septum, and in most taxa,
hydrostatic pressure in the conidium forces the
sudden eversion of the electron-lucent septal
wall layer. The often-visible line of demarcation
between the conidial body and the papilla (the
everted septum) is the margin of the outer wall
layer. In the bitunicate conidia [Fig.8.1(8)] of
species ofErynia,Furia,Pandora,Strongwell-
sea, andZoophthora, the outer wall layer may
separate from the spore surface in liquid and
give a false impression that the spores are
monosporic sporangioles; conidial wall layers
of the unitunicate conidia [Fig.8.1(5, 6)] in all
other genera do not separate (Remaudie`re and
Hennebert 1980 ).
Secondary conidia may be formed by spe-
cies in all genera, exceptMassospora, when
conidia land on substrates unsuitable for initi-
ating germ tubes. The morphological types of
secondary conidia are discussed in detail by
Ben-Ze’ev and Kenneth ( 1982 ). Forcibly dis-
charged secondary conidia are uniformly shot
off by papillar eversion regardless of the mode
of discharge for the primary conidia. Forcibly
discharged secondary conidia in genera that
may produce passively discharged capilliconidia
[Fig.8.1(9),Zoophthora radicans] may form for-
cibly discharged tertiary conidia or passively
dispersed tertiary capilliconidia. Resporulation
by passively dispersed capilliconidia is always
by production of another capillary conidiophore
and capilliconidium. The genus Orthomyces
(Steinkraus et al. 1998 ) was described as differing
fromZoophthorain part because the secondary
capilliconidia of Orthomyces aleyrodisone areZygomycetous Fungi: Phylum Entomophthoromycota and Subphyla Kickxellomycotina,... 217