Insect Control: Biological and Synthetic Agents - Index of

11: Entomopathogenic Fungi and their Role in Regulation of Insect Populations 417
have also been tested against grain borers (Smith
et al., 1999).
11.7. Development as Inoculative
Microbial Control Agents
Inoculation biological control is defined as
The intentional release of a living organism as a
biological control agent with the expectation that it
will multiply and control the pest for an extended
period, but not that it will do so permanently.
Eilenberg et al. (2001)
This is desirable because only a limited amount of
inoculum (in vivo or in vitro acquired material) is
released at each treatment. The inoculum is expected
to proliferate and control the target pest
over time, but additional releases would normally
be needed in the future (e.g., next cropping season).
Entomophthoralean fungi may fit very well in inoculation
biological control because they have the
ability to establish epizootics quickly in target pest
populations, have a narrow host range, and are able
to persist in the target insect population.
Inoculation biological control is being used in
northeastern USA to initiate epizootics of E. maimaiga
in populations of L. dispar (Hajek and Webb,
1999; Pell et al., 2001). Resting spores are collected
on sites with high populations of the target insect
and high prevalence of the fungus, and then spread
on soil in areas without the fungus, but with host
infestation. Although the fungus is well established
throughout the host’s distribution area, the host
continues to spread, and cadavers are distributed
along the leading edge of this spread in an effort to
halt the destruction caused by this introduced pest.
There are other possibilities for inoculative biological
control using fungi, such as inoculation of a
small amount of B. brongniartii to control soil
dwelling beetles from Scarabaeidae (Eilenberg
et al., 2000b). Another possibility would be use of
E. muscae and S. castrans against cabbage root flies
(D. radicum and D. floralis). Moreover, indoor,
inoculative releases to control M. domestica could
be based on in vivo cultures of E. muscae or
E. schizophorae (e.g., Kuramoto and Shimazu,
1997). Conidia are sufficiently persistent in the environment
for this release (Kalsbeek et al., 2001b).
Indoor stables are favorable for studies on fungus
dispersal in a confined environment.
Dissemination is essential for the success of inoculation
biological control. Pell et al. (1993) and
Furlong et al. (1995) demonstrated that autodissemination
of Z. radicans was possible in field populations
of the diamondback moth P. xylostella in
Malaysia by using a pheromone trap to attract
adult insects. After the adults left the trap, they
dispersed the fungus to both larvae and adults, and
larvae became infected. Further experiments of inoculative
releases in England demonstrate that it
is possible to induce epizootics in P. xylostella
using Z. radicans (Pell and Wilding, 1994). Other
examples are provided by Vega et al. (2000).
11.8. Use in Classical Biocontrol
Classical biological control is defined as
The intentional introduction of an exotic biological
control agent for permanent establishment and longterm
pest control
Eilenberg et al. (2001)
It is desirable from the point of view that limited
inoculative releases of an organism will result in a
long-lasting control of a pest (often an introduced
pest species). Because the introduction of an exotic
species has the potential of irreversible direct effects
on nontarget species, or indirect effects through host
depletion, it is important to gain as much information
on the potential candidate’s host range and
epizootiology as possible prior to its introduction
(Hajek and Butler, 2000; Hajek and Goettel, 2000;
Goettel and Hajek, 2001; Goettel et al., 2001).
There is great potential in the use of entomopathogenic
fungi in classical biological control, especially
against introduced pests. Fungi from Entomophthorales
possess several characteristics favoring
their use in classical biological control; they can
establish epizootics quickly, they have mostly a
narrow host range, and they persist in pest populations
and in the environment. Unfortunately, in
most cases, it is not known whether or not a given
species is already present in a locality, and the
tools needed for detailed studies of their spread
after release (e.g., isolate specific characterization)
are usually not fully developed (see Section 11.4).
As early as 1909, E. maimaiga infected gypsy
moths, L. dispar, were collected in Japan and released
in Boston, USA, in an attempt to control
introduced L. dispar, but the fungus was not observed
in local L. dispar populations for many
years. It was, however, discovered in northeastern
USA in 1989 and has now spread into many other
areas within North America where L. dispar infestations
were prevalent. It has not been ascertained if
the fungus now commonly present is a result of the
early release or if it was later accidentally imported
(Hajek et al., 1995; Pell et al., 2001). A recent introduction
of E. maimaiga into Bulgaria was successful
(Pilarska et al., 2000).