Introduction to Fungi, Third Edition

362 HYMENOASCOMYCETES: PYRENOMYCETES
Fig12.34 Stromata of Cordyceps sinensis growing from insect
larvae. Image kindly supplied byY.-J.Yao.
and western China, Tibet and Nepal (Jiang & Yao,
2002). The cylindrical perithecial stromata may
be 10 cm or more in length and bundles of dried
stromata are sold commercially. The anamorph
is Hirsutella sinensis (Liu et al., 2001). The conidiogenous
cells are tightly packed together on the
surface of a stroma.
The ecological role of Cordyceps spp. on insects
is difficult to evaluate. Evans and Samson (1982,
1984), judging by the large numbers of stromata
collected on worker ants in tropical forests, were
of the opinion that they exerted a controlling
effect on population size.
Cordyceps ophioglossoides grows in woods on
the subterranean ascocarps of the hart’s truffle
Elaphomyces, forming bright yellow mycelial
stands over its surface. Brown club-shaped
perithecial stromata grow above ground in
autumn (Plate 4f). Cordyceps capitata grows in
similar situations. Phylogenetic analyses using
nuclear and mitochondrial ribosomal DNA
derived from 22 species of Cordyceps and their
known anamorphs have shown that four species
of Cordyceps parasitic on Elaphomyces have very
close similarity to two species which parasitize
the nymphs of cicadas, and have probably
evolved from them, an example of ‘interkingdom
host-jumping’. These related species have been
grouped together in a ‘truffle cicada clade’ and
it has been suggested that the truffle cicada
clade separated from other Cordyceps clades
about 43 + 13 million years ago (Nikoh &
Fukatsu, 2000). Cicada nymphs develop for
several years underground, feeding on xylem
sap from the host trees with which they are
associated. In this respect their physiology is
similar to that of Elaphomyces spp., which are
mycorrhizal partners of trees, obtaining nutrients
from them. Nikoh and Fukatsu (2000) have
speculated that the overlapping niches of the
species of Cordyceps which parasitize cicadas and
those which parasitize hart’s truffles may have
promoted this interkingdom host jumping.
Species of Cordyceps reproduce asexually,
some having more than one anamorphic state,
i.e. with synanamorphs (Hodge, 2003).
Considerable research attention has been
focused on the three anamorphs Beauveria
bassiana, Metarhizium anisopliae and Tolypocladium
inflatum (Figs. 12.35a c). The first two have
potential for the biological control of insect
pests, whereas Tolypocladium inflatum is the
source of the immunosuppressant drug cyclosporin
A (Fig. 12.24a).
Beauveria bassiana
This is the conidial form of Cordyceps bassiana
(Huang et al., 2002) and causes the serious white
muscardine disease of silkworm (Bombyx mori)
larvae, which is a threat to silk production. This
species has been known for well over a century
and is of historical interest because Agostino
Bassi, who studied the fungus around 1835,
proposed the germ theory of disease on the
basis of his results. This preceded by several years
the publications of Robert Koch, who is usually
given credit for the formal proof of pathogenesis
by micro-organisms. Beauveria bassiana is widely
distributed in the soil, usually associated with
diseased insects (Domsch et al., 1980). Species of
Coleoptera, Diptera, Lepidoptera and other
groups, including Arachnida, are covered by
white dusty raised tufts of hyphae bearing