Agriculture Reference
In-Depth Information
Yonker, 2003). Sanitation alone may not
explain the complexity of cockroach
infestation because many other factors and
their interactions are involved, including
the density of residents living inside the
premises, building effects and role of
outdoor reservoir populations (Rivault and
Cloarec, 1995; Robinson, 2002). Neverthe-
less, the effects of food and water deprivation
on cockroach biology support the import-
ance of sanitation for cockroach management
using toxic baits (Lee and Lee, 2000a).
Proper sanitation alone is not suffi cient
to reduce cockroach population size
because many pest cockroaches are able to
withstand food and water deprivation for a
period of time (Willis and Lewis, 1957).
However, Lee and Heng (2000) reported that
cockroaches are more susceptible to insecti-
cide treatment under starvation stress.
Removal of food and water sources directly
reduces competition between bait and other
food sources, induces stress among cock-
roaches for resource foraging (Ballard
et al
.,
1984; Barcay and Bennett, 1991) and has a
greater impact on cockroach populations
when toxic bait is applied (Lee and Soo,
2002a). Durier and Rivault (2001) demon-
strated that the attractiveness of cockroach
bait is reduced if there are other food
sources present nearer to their harbourage.
In the fi eld, Rivault and Cloarec (1991)
found that German cockroaches ate the food
sources they fi rst encountered and foraged
further away once the food source was
depleted. Consequently, cockroaches that
are fully fed and satiated may not respond
well to bait. Cockroaches react to food and
water deprivation by increasing their time
spent in movement, foraging distance and
speed (Barcay and Bennett, 1991). This is
useful for baiting of cockroaches because it
eventually leads to a higher chance of bait
being encountered and consumed in a larger
amount. Under food and water deprivation,
cockroaches readily eat more bait as their
body reserves start to decrease (Smith and
Appel, 1996). A moisture source is import-
ant for the survival of cockroaches (Appel
et
al
., 1983; Appel, 1995). This characteristic
is particularly favourable for baits with a
high moisture content and may explain why
gel formulations are more preferable and
have faster killing effects than other formu-
lations in laboratory and fi eld studies
(Appel and Benson, 1995; Appel and Tanley,
2000; Buczkowski
et al
., 2001; Appel, 2003).
Ageing and contamination of bait
When baits are applied, they are subjected
to interaction with the ambient environ-
mental conditions. The effi cacy of baits
depends on the ability to prolong their
attractiveness over time. Feeding activity
of cockroaches varies at each interval of
their developmental stage. For example,
B.
germanica
and
P. americana
nymphs ingest
more food during the initial stage of each
stadium and gradually reduce their intake
to a low level until next moulting (Richter
and Barwolf, 1994; Valles
et al
., 1996) and
females feed little for a few days before
ovulation and only resume feeding after
oothecae are dropped (Bell
et al
., 2007).
After application, moist baits are suscep-
tible to desiccation, and the rate of desic-
cation depends on the formulation itself
and on conditions such as temperature,
humidity, air currents and the amount of
surface area exposed to desiccation (Appel
and Benson, 1995). The amount of water
loss for gel baits was reported to be around
80% after 3-4 days of desiccation (Appel,
1992; Appel and Tanley, 2000; Appel,
2003). Appel and Benson (1995) found that
the fi nal texture of dried bait is more
important than the amount of water loss in
determining its attractiveness and palata-
bility. They demonstrated that dried baits,
which were hard and not palatable to
German cockroaches, resulted in faster
mortality after they were ground and fi ltered
into fi ne particles similar in size to a powder
bait formulation. Although most moist baits
eventually become solid, hard, and unpalat-
able to cockroaches, there are formulations
that can remain soft, sticky and palatable to
cockroaches (Appel and Benson, 1995;
Appel and Tanley, 2000; Appel, 2003).
Studies of
B. germanica
showed that the
attractiveness and palatability of 2.15%
hydramethylnon gel bait and 0.25%
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