Agriculture Reference
In-Depth Information
Biological Control of Subterranean
Termites
percent of colonies that were 6 m or more
away from the treated structures were not
detected for the remainder of the study.
There was a 67% decrease in activity in the
inner monitors for imidacloprid treatments
and complete cessation for 3 years in the
fi pronil treatments (Vargo and Parman,
2012). The data support the fact that both
imidacloprid and fi pronil treatments have
colony-level effects; however, the precise
mechanism leading to these reductions
remains unknown. These studies support
the use of perimeter and spot treatments to
control subterranean termites, thereby
reducing the amounts of insecticide
applied.
Molecular techniques have also been
used to demonstrate the effectiveness of
baiting. Of the 36
Reticulitermes
colonies
around structures identifi ed and baited
with hexafl umuron, only one was located
the following year. This colony disappeared
in year two (Vargo, 2003). Fifteen colonies
of
C. formosanus
were identifi ed with
microsatellite genotyping and baited with
0.5% novifl umuron bait (Husseneder
et al.
,
2007). After 12 months, all termite activity
had stopped. Lufenuron baits were also
effective in controlling
R. hesperus
as
shown with the aid of molecular techniques
(Haverty
et al.,
2010). Some of the
advantages afforded by these techniques are
that they only require a few termites for
analysis, they establish a link between
baiting and termite reductions, and they
identify colonies that have and have not fed
on the baits (Haverty
et al
., 2010).
It is also noteworthy that no two struc-
tures treated for subterranean termites are
ever identical, making meaningful statistical
comparisons often diffi cult. To overcome
this, Puckett
et al.
(2011) designed an
interesting scoring method (rubric) that
incorporates the termite species, the number
of mud tubes, the conducive conditions and
the construction type. It is assumed that
diffi culty in treating is positively correlated
to the total diffi culty score (TDS). Of the re-
treated structures, 75% had higher than
average TDS scores. Their rubric might be a
useful way of categorizing treatments for
statistical analyses.
The potential use of bacteria, fungi and
nematodes in controlling termites was
reviewed by Verma
et al.
(2009). Even
though the use of entomopathogens has
been proposed for decades, it has not been
demonstrated to actually control termites in
structures. To be successful, the virulent
agent must self-replicate and be transmitted
by termites through social interactions to
create an epizootic, killing the colony
(Chouvenc and Su, 2010). The pathogens
must have suffi cient virulence that they are
rapidly spread through the colony, causing
its decline. Over the years, a divergence of
opinions regarding their potential as effect-
ive biological control agents has emerged.
In a review of
Metarhizium anisopliae
, Rath
(2000) states that 'Termites live in an
environment which should be conducive to
good effi cacy and spread of fungi'. It is more
complicated, however, as revealed by recent
studies. Subterranean termites utilize a
number of different strategies including
grooming, cellular encapsulation and gut
antifungal activity to reduce the effective-
ness of fungal agents (Chouvenc and Su,
2010). Some recent research suggests that
antifungal compounds are produced in the
salivary glands and excreted on to the
cuticle. Chouvenc and Su (2010) states,
'With the current knowledge of the termite
fungus interaction and with the available
technologies, it is not realistic to control
subterranean termite colonies with a classi-
cal biological control approach because the
conditions in the termite habitat does not
allow the fungus to survive, replicate and
disperse within the population'. Following
are a number of termite behaviours and
responses that could be considered as prime
reasons why biological control is a failure in
termites.
Grooming behaviour
C. formosanus
workers reared in isolation
are highly susceptible to the entomopatho-
genic fungi
Paecilomyces fumosoroseus
,
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