August 2022 - 15

DR. BUGS
All three mechanisms described
Figure 3. Western flower thrips larva. Larvae are less susceptible to infection by
entomopathogenic fungi than adults.
allows the growing hyphae to
create mechanical pressure, which
weakens the cuticle and facilitates
infection or entry into the body
of an insect pest. Therefore,
infection by an entomopathogenic
fungus involves: 1) attachment of
conidia to the insect pest cuticle,
2) germination or germ tube
formation, and 3) penetration
through the insect pest cuticle.
However, insect pests have
developed several mechanisms
that can inhibit infection by
entomopathogenic fungi, including:
1) production of antimicrobial
compounds in the cuticle that
inhibit fungal attachment and
decrease infection, 2) shedding
of the cuticle when molting
(ecdysis), and 3) implementing
behavioral responses such as
grooming and burrowing.
The antimicrobial compounds
produced by the cuticle can
inhibit spore germination
and growth of hyphae, thus
suppressing the ability of an
entomopathogenic fungus to
enter the insect pest body. In
addition, compounds in the
cuticle can resist mechanical
penetration or inhibit fungal
degradation enzymes.
Molting mitigates infection by
an entomopathogenic fungus
by reducing the time that an
entomopathogenic fungus
can infect an insect pest. For
example, the molting of aphids
and thrips may contribute to
insufficient mortality when using
entomopathogenic fungal-based
insecticides, such as BotaniGard,
Ancora, and Met52.
Some insect pests groom
themselves, which removes
fungal spores from the cuticle
and reduces infection. In addition,
tunneling or burrowing into the
growing medium may result in
removing fungal spores (e.g.,
fungus gnat larvae and western
flower thrips, Frankliniella
occidentalis, second instar
larvae or adults when entering
or emerging from the growing
medium).
above can reduce the ability of an
entomopathogenic fungus to infect
insect pests, thus decreasing their
effectiveness in managing insect
pest populations.
The cuticle can vary depending
on the specific life stage (larva,
nymph and adult) of an insect
pest. For example, the larvae and
adult life stages of western flower
thrips are susceptible to infection
by most entomopathogenic fungi.
However, adult western flower
thrips are more susceptible to
infection by entomopathogenic
fungi than the larvae. The difference
in life stage susceptibility may be
associated with the removal of
fungal spores that are attached to
the cuticle surface when western
flower thrips larvae shed their outer
cuticle during molting. As such,
entomopathogenic fungi that are
unable to penetrate the cuticle
before the onset of molting will
not infect western flower thrips.
In addition, the larvae have a
thicker cuticle, which may decrease
penetration, thus rendering the
larvae more resistant to infection.
A way to overcome insect
pests removing fungal spores
during molting, and subsequently
enhancing the effectiveness of an
entomopathogenic fungus, is to
combine an entomopathogenic
fungal-based insecticide with an
insecticide product that contains the
insect growth regulator azadirachtin
(AzaGuard, Azatin, Azatrol, Ornazin,
and Molt-X). Azadirachtin is an
ecdysone antagonist. Ecdysone
is the juvenile hormone that is
responsible for initiating molting.
Azadirachtin delays the molting
process by inhibiting the production
of ecdysone. Consequently, by
delaying the molting process, the
entomopathogenic fungus can
penetrate the cuticle and infect an
insect pest before molting occurs.
However, the synergistic effect of
using azadirachtin in conjunction
with an entomopathogenic
fungus may not occur for all
entomopathogenic fungi.
Entomopathogenic fungi are
effective in managing insect pest
populations when applied early
in the production cycle and when
insect pest populations are low.
However, infection and subsequent
mortality take longer (in days)
than most commonly used
insecticides.
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GREENHOUSE PRODUCT NEWS 15
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August 2022

Table of Contents for the Digital Edition of August 2022
