The Order Entomophthoralesis notable because
it includes many fungi that parasitize insects, and that
can cause spectacular population crashes of their
insect hosts (discussed in Chapter 15). Many are host-specialized, typically infecting only a narrow range of
insects, but others have relatively broad host ranges.
Techniques have been developed to mass produce
some of these fungi in solid or liquid culture systems,
raising the prospect of using them as practical biocontrol
agents of insect pests. The Entomophthorales are
notable for the way in which they are dispersed. As
shown in Fig. 2.11a, the hyphae emerging from a dead
insect produce sporangiophores, each bearing a large
sporangium at its tip. The tip of the sporangiophore
has a columella, which bulges into the spore and
is double-walled (one wall being the tip of the columella,
and the other being the wall of the sporangium).
The progressive build-up of turgor pressure causes the
sporangium to be shot suddenly from the columella,
projecting the sporangium to a distance of about 4 cm
(Webster 1980). (Technically, the sporangium in this
case is a single spore, which is not enclosed in a spo-
rangium wall, so it is termed a conidium, like the many
types of conidia produced by the Ascomycota – see
later.) The sporangium (conidium) is sticky and must
adhere to an insect in order to infect. If it does not land
on an insect it will germinate to produce a secondary
conidium, which is similarly dispersed, and this pro-
cess will be repeated until the conidium lands on a suit-
able host or until the nutrient reserves are exhausted.
Chapter 15 provides a much fuller account of these and
other insect-pathogenic fungi.26 CHAPTER 2
Fig. 2.11(a) Sporangia of insect-pathogenic members of the Entomophthorales (e.g. Entomophthora, Pandora spp.) are
released and function like spores. (b) Pilobolus, a common fungus on herbivore dung, has a sporangium containing many
spores. It is mounted on a vesicle, which ruptures at maturity to shoot the sporangium onto surrounding vegetation
(Chapter 10). (c) Piptocephalisis a parasite of other Zygomycota. It produces branched sporangiophores with merospor-
angia(each containing a few linearly arranged spores) at the branch tips.Fig. 2.12A mature, thick-walled, warty zygospore (sexual
spore) of Rhizopus sexualis, produced by the fusion of
two gametangia. The bulbous swellings on either side are
termed suspensors.FB4eC02 04/20/2005 02:52PM Page 26