Agriculture Reference
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indoxacarb gel bait after 7 days of ageing
under room conditions remained compar-
able to those of freshly deposited baits,
whereas this was not true for aged 0.05%
abamectin powder bait (Appel, 2003;
Nalyanya
et al
., 2001). Interestingly, toxi-
cants from cockroach bait can remain
within a cadaver for a long time. Cadavers
of oriental cockroaches that had fed on
0.05% fi pronil gel bait remained toxic after
storage at 33-76% relative humidity and
28°C for a maximum duration of 7 weeks.
Exposure of healthy adult conspecifics to
these fipronil-poisoned cadavers resulted in
64-100% mortality (le Patourel, 2000).
Besides interaction with the ambient
environment, repellent substances may con-
taminate cockroach baits or the areas where
baits are to be applied. Appel (2004) found
that placement of baits of all formulation
types (gel, dust, dry and bait station) on a
surface contaminated with compounds
such as repellent insecticides, cleaning
agents, cooking oils and solvents reduced
the consumption of bait by German cock-
roaches and increased the kill time. In
addition, the surface of dry bait con-
taminated with repellents had lower bait
consumption and toxicity, whereas direct
contamination did not affect gel baits (and
in some cases even increased gel bait
toxicity). Appel (2004) suggested that con-
taminants may have been absorbed by the
gel bait and only a negligible amount was
available at the surface of the bait. Exposure
of cockroaches to repellents and sublethal
doses of insecticides disrupts activities
such as induced dispersion, feeding inhib-
ition and avoidance behaviour (Bret and
Ross, 1985; Haynes, 1988; Barcay
et al
.,
1990), which eventually reduces their
ability to forage effi ciently.
(Table 5.1). However, many of the evalu-
ations of physiological resistance among
fi eld-collected
B. germanica
were conducted
before new insecticide groups were used in
the fi eld (Holbrook
et al
., 2003; Chai and
Lee, 2010). Therefore, there is a possibility
that the selection pressure from previously
used insecticides could have conferred
cross-resistance toward the newer insecti-
cides used in cockroach baits (Holbrook
et
al
., 2003; Kristensen
et al
., 2005; Gond-
halekar and Scharf, 2012). For example,
based on a topical LC
50
bioassay, a fi eld
strain (Cr-Al) from North Carolina that had
no history of fi pronil treatment showed 17-
fold greater resistance to fi pronil compared
with that of a laboratory susceptible strain
(Holbrook
et al
., 2003). At present, there are
no reports of control failure of bait products
containing these active ingredients against
B. germanica
due to physiological insecti-
cide resistance. Bait formulated as palatable
food mixture is one reason why physio-
logical insecticide resistance does not lead
to control failure among these newer
insecticides. When cockroaches feed on a
highly palatable bait, the toxicant is
normally ingested at higher doses than that
required to cause a lethal response
(Holbrook
et al
., 2003; Gondhalekar
et al
.,
2011; Gondhalekar and Scharf, 2012). It was
noted that
B. germanica
consumed 150 to >
1300 times and 218-441 times the LD
50
of
fi pronil and indoxacarb, respectively, after
24 h of exposure to the gel baits (Bayer
et
al
., 2012). In another study, a fi eld strain of
B. germanica
was 36-fold more resistant to
fi pronil compared to a laboratory susceptible
strain when the insecticide was applied
topically; two- to three-fold more resistance
was achieved when they were fed 0.01%
fi pronil bait (Gondhalekar
et al
., 2011).
Consumption of active ingredients in such a
great amount eventually kills all of the
cockroaches and development of resistance
may not occur, or may be delayed in
cockroach populations (Holbrook
et al
.,
2003; Gondhalekar and Scharf, 2012).
Nevertheless, the frequency of a resist-
ance gene within a
B. germanica
population
may increase if a portion of the cockroach
population survives and breeds under
Resistance to insecticide baits
Resistance to insecticides is a major concern
in the management of
B. germanica
. Since
the introduction of newer insecticides used
in cockroach bait, low to moderate levels of
physiological resistance of
B. germanica
to
some of these insecticides has been detected
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