untitled

Even more important is the fact that epizootics caused
by insect-pathogenic fungi are strongly influenced
by environmental factors. Insect-pathogenic fungi in
general require a high humidity for spore germina-
tion and also for sporulation on the dead insect
hosts. Thus, natural epizootics are unpredictable, and
even commercially applied inocula of these fungi are
prone to fail unless the environmental conditions are
favorable.

Developments in practical biocontrol

Some of the limitations in natural biocontrol can be

overcome by using commercially produced inocula if

these are formulated to high standards. Feng et al. (1994)

reviewed the technology for producing B. bassiana,

which is commercially attractive as a biocontrol agent

because of its wide host range. These authors reported

that about 10,000 tons of spore powder containing

314 CHAPTER 15

Fig. 15.5Proposed life cycle of Coelomomyces

psorophorae, which has an obligate alternation

of generations. Diploid phase in a mosquito

larva:a motile zygote attaches to the larva,

encysts, produces an appressorium, then

penetrates the host and produces a weakly

branched mycelium. This gives rise to thick-

walled resting spores that are released when

the mosquito host dies. Haploid phase in a

copepod (Cyclops vernalis): meiosis occurs in

the resting sporangia and haploid zoospores

of different mating types are released. These

infect the copepod and produce a thallus

that eventually gives rise to gametangia. The

gametangia release motile gametes that fuse

either inside or outside the host. The resulting

diploid zygote can only infect a mosquito

larva. (Adapted from Whisler et al. 1975.)

Fig. 15.6Numbers of aphids (Aphis fabae)

in a broad bean crop during a growing

season in Britain (broken line) and per-

centage infection by the pathogenic fungus

Pandora neoaphidis (solid line). (Based on

data in Wilding & Perry 1980.)