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(Cohen
et al
., 1987). The same study found
the carbohydrate was taken mainly during
the fi rst week and then less was taken in
each subsequent stadium, whereas protein
was constantly ingested in a lower pro-
portion throughout each life stage. If they
were able to self-select nutrients, they grew
normally by acquiring the nutrients needed
at each nymphal development stage. In
another study, Raubenheimer and Jones
(2006) reported that, when subjected to
nutrient defi ciencies,
B. germanica
pre-
ferred to self-select an imbalanced food
that compensated for the nutrient they
were lacking to a balanced food. The ability
to distinguish food of different nutritional
value may be due to specifi c nutrient
learning in cockroaches (Raubenheimer
and Jones, 2006). Associative learning has
been reported in
Periplaneta americana
,
whereby they were able to associate food
odours with proteins (Gadd and Rauben-
heimer, 2000). Therefore, several food
types, mainly containing three macro-
nutrients (carbohydrate, lipid and protein),
are used in the matrices of cockroach
baits.
In studies of the feeding patterns of pest
cockroaches, Tsuji (1965, 1966) showed that
several constituents from rice bran, some
carbohydrates, and several substances from
fatty acids and their related compounds
were attractive and acted as a feeding
stimulant to
P. americana
,
Periplaneta
fuliginosa
and
B. germanica
. Sugars,
including glucose, galactose, fructose,
sucrose, maltose and
L
-arabinose, can
stimulate feeding in cockroaches (Tsuji,
1965; Tsuji and Ono, 1969) and are used in
cockroach baits (Gore and Schal, 2004;
Bayer
et al
., 2012). Peanut butter as an
attractant is also used as a food base in most
commercial baits (Appel, 1990; Nalyanya
and Schal, 2001; Wang and Bennett, 2006).
Recently, Karimifar
et al
. (2011) identifi ed a
volatile compound, 1-hexanol, from peanut
butter that acts as a semiochemical that
attracts
B. germanica
. Protein sources
derived from poultry liver, silkworm pupae,
and hydrogenated soy protein have been
used in bait mixtures as feeding stimulants
(Wolfe
et al
., 1997). Other additives are
added to bait mixtures to prolong their
lifespan. For example, p-nitrophenol
inhibits the growth of mould on bait (Rust
et
al
., 1991) and polyols, such as sorbitol,
mannitol and glycerol, act as humectants to
stabilize and retain moisture content in the
bait (Schal and Hamilton, 1990).
Cockroach baits are available in various
formulation types. Gel and paste baits are
the most common formulations with high
moisture content; gels have a higher water
content (39-80%) than pastes (14-30%)
(Appel, 1992; Appel and Benson, 1995;
Appel and Tanley, 2000; Appel, 2003). Gel
and paste baits can be applied directly in
cockroach-infested sites such as cracks,
crevices and voids using a syringe or bait
gun (Reierson, 1995). Dry fl owable powder
baits also are formulated for use in cracks
and crevices to reach deep spaces where the
application of gel and paste is restricted
(Dhang, 2011). Granular baits are designed
for use outdoors against peridomestic pest
cockroaches. They can be scattered into
outdoor cockroach harbourage sites such as
tree holes, fi rewood piles, heavy ground
cover, landscape timbers and landscape
mulch (Benson and Zungoli, 1997). Baits
are also available in ready-to-use container-
ized stations (Reierson, 1995).
Bait was previously considered to be
ineffective in attracting cockroaches over
distance (Reierson, 1995). Laboratory
olfactometer experiments have, however,
demonstrated that baits were able to induce
upwind movement of cockroaches. Traps
baited with commercial baits placed 25-30
cm away from corners and edges of walls
successfully caught cockroaches in fi eld
evaluations (Silverman and Bieman, 1996;
Nalyanya
et al
., 2001). Attractiveness alone,
however, is not suffi cient to prove whether
bait is intrinsically effective. A substance
can act as both an attractant and a feeding
stimulant but a substance that is attractive
may not necessarily stimulate feeding and
vice versa (Tsuji, 1965). An attractant
functions by attracting cockroaches toward
bait, whereas a feeding stimulant induces
and promotes increased consumption of the
bait (Durier and Rivault, 2000a). The
amount of bait consumed is an important
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