Insect Control: Biological and Synthetic Agents - Index of

of interaction between different host aphid species,
other natural enemies (predators, parasitoids), and
fungal pathogens (Baverstock et al., 2008; Roy
et al., 2008).
A11.6. Production
The production of microsclerotia by M. anisopliae
in vitro has been found through varying the concentration
of carbon and carbon/nitrogen concentrations
(Jaronski and Jackson, 2008). These tight hyphal
bundles are more resistant to desiccation and could
be rehydrated to produce hyphae, sporulate, and infect
the sugar beet maggot (Tetanops myopaeformis).
The production of microslerotia in liquid culture
could provide a novel method for biopesticide production
against soil dwelling pests, as well as a possible
increased persistence for Metarhizium in soil.
In a very different approach to application, the
entomophthoralean pathogen Neozygites fresenii
(Entomophthorales: Neozygitaceae) has been collected
as cadavers of the host Aphis gossypii (Homoptera:
Aphididae), dried using salt or silica gel and
stored frozen (Steinkraus and Boys, 2005) to be used
to inoculate cotton fields for aphid control in
subsequent seasons.
A11.7. Role of Metabolites
A number of studies have advanced knowledge
on the genetics and function of secondary metabolites
and toxins from entomopathogens, especially
Beauveria and Metarhizium, which can be useful
in understanding infection processes and developing
biocontrol. Large EST or genome studies have
demonstrated regulation of known enzyme or
toxin genes during exposure to the cuticle or other
conditions (see next section) and several studies
demonstrated the involvement of well known metabolites
in virulence.
Bassianolide, a cyclooligomer depsipeptide secondary
metabolite from B. bassiana, was shown
to be a highly significant virulence factor through
targeted inactivation studies. Disruption of bassianolide
did not affect another metabolite, beauvericin
(Xu et al., 2009), another cyclodepsipeptide,
which was identified as a nonessential virulence factor
during infection of Galleria mellonella, Spodoptera
exigua, and Helicoverpa zea (Xu et al., 2008).
Beauvericin was also highly toxic in vitro to cells of
the fall armyworm, S. exigua (Fornelli et al., 2004).
However, Eley et al. (2007) showed that another
metabolite of B. bassiana, tenellin,hadnorolein
virulence.
A11: Addendum 435
The cyclic depsipeptides destruxins, produced
by M. anisopliae, have insecticidal, antiviral, and
phytotoxic abilities and are also studied for their
toxicity to cancer cells. Gene expression studies
on Drosophila melanogaster following injection of
destruxin showed a novel role for destruxin A in
specific suppression of the humoral immune response
in insects (Pal et al., 2007).
Subtilisins (Pr1) are known to be involved in virulence
of some entomopathogenic fungi. Metarhizium
strains with broad host ranges expressed up to
11 subtilisins during growth on insect cuticle (Bagga
et al., 2004) and up to 8 in Beauveria (Cho et al.,
2006a). Pr1 was also shown to be upregulated during
mycelial emergence in the host (Small and
Bidochka, 2005), suggesting that, as the nutrition
within the host is depleted, Pr1 is upregulated to
assist breaching the host cuticle again.
A zinc-dependent metalloprotease, ZrMEP1, was
isolated from Zoophthora radicans, the first report
of this type of metalloprotease from an entomopathogenic
fungus. It appears to have a role in the
infection process (Xu et al., 2006).
A11.8. Advances in Molecular Genetics
Recent studies identified many genes involved in
the infection process of fungi. For Metarhizium
and Beauveria, they show different gene expression
depending on growth form, host, and environment.
Cho et al. (2006a, b), conducted extensive expression
sequence tag (EST) analysis of B. bassiana
cDNA-libraries from conidia, blastospores, and
under different growth conditions, with around
4000 sequences isolated. The evidence demonstrates
highly plastic gene expression depending on cDNA
library. Pathan et al. (2007) used analyses of gene
expression patterns through cDNA-AFLPs of a
B. bassiana isolate grown on cuticular extracts of
various insects and synthetic medium. In general,
they found the activity on cuticular extracts from
diverse insects was similar, suggesting a relatively
generic response to the penetration of cuticle may
be indicative of a broad host range. In contrast,
genes expressed on synthetic medium were quite
different from those on cuticle.
Freimoser et al. (2005) examined the response of
M. anisopliae to different insect cuticles using cDNA
microarrays constructed from ESTs. They found unique
expression responses for different insect cuticles, indicating
the fungus could react specifically to species of
insects. M. anisopliae had several forms of catabolic
enzymes which were regulated by different sugar levels.
This provided more evidence that the fungus could
respond to nutrition in different environments.