Sustainable Cockroach Management Using Insecticidal Baits: Formulations, Behavioural Responses and Issues - Urban Insect Pests: Sustainable Management Strategies - page 73

this behaviour allows them to gain nutrients
needed for growth into second instar
nymphs (Kopanic et al ., 2001).
For a toxicant to be transferred hori-
zontally among cockroaches through copro-
phagy, it must be stable during passage
through the digestive tract and slow acting
enough to allow its excretion before insect
death (Kopanic and Schal, 1999). By tracing
dyed rat chow within the digestive tract of
German cockroaches, Kopanic and Schal
(1999) determined that at least 12 h was
required for insecticide baits to be defecated;
however, this time interval could be shorter
for more liquid formulations such as gel and
paste baits. Among the active ingredients
used in cockroach baits, hydramethylnon
has been shown to transfer horizontally via
coprophagy in several cockroach species,
including B. germanica , P. americana and P.
fuliginosa (Silverman et al ., 1991;
Shimamura et al ., 1994; Kopanic and Schal,
1999). Silverman et al . (1991) confi rmed
that faecal materials obtained from the
abdomen of hydramethylnon-fed German
cockroaches were responsible for the hori-
zontal transfer, whereas residues secreted
from the head were not toxic and contact
with hydramethylnon bait or faeces was not
lethal. Based on the amount of radiolabelled
hydramethylnon bait ingested, Silverman et
al . (1991) found that 22.3-44.7% of the
ingested hydramethylnon was excreted in
faeces for all life stages of the German cock-
roach and 51% of this was the unmetabolized
parent compound of hydramethylnon.
Kopanic and Schal (1997, 1999) demon-
strated that adult cockroaches were respon-
sible for the translocation of insecticide bait
via coprophagy to the sedentary early
nymphs. In their experiment, when food
was located near the harbourage and
hydramethylnon (2.15%) bait was placed
124-150 cm away from the harbourage,
nymphs had low mortality rates when adult
cockroaches were excluded from access to
the bait. When adults had access to the bait
and nymphs did not, however, high
nymphal mortality was recorded after 3
days.
The magnitude of coprophagy in young
nymphs is infl uenced by the availability of

food and its distance from the harbourage
(Kopanic and Schal, 1997, 1999) because
German cockroach nymphs were shown to
engage in more coprophagous behaviour
when food was placed farther away from
the harbourage. Because the fi rst instar
nymphs were less effi cient foragers and
tended to stay close to the harbourage, their
intake of adult faeces was consistent be-
tween experiments conducted in a
laboratory test arena (120  30 cm) and in a
vacant apartment room (240  360 cm).
However, second instar nymphs were found
to be more effi cient foragers than the fi rst
instars (Dabouineau and Rivault, 1995). The
difference in coprophagous behaviour be-
tween fi rst and second instar nymphs may
be due to their different foraging abilities
and body reserves. During a 24-h starvation
period, fi rst instar nymphs ate three times
more faeces by mass than regular food. In
contrast, second instar nymphs with two
times more body mass and three times
greater food consumption ingested lower
amounts of faeces than fi rst instar nymphs
(Kopanic and Schal, 1999). As the starvation
period increased from 24 to 48 h, second
instar nymphs resorted to coprophagy and
ate as many faeces as the fi rst instar nymphs
(Kopanic and Schal, 1999). These fi ndings
show that coprophagy is an adaptive behav-
iour. Although faeces provide minimal
nutrients for newly hatched nymphs, they
are poor foragers and faeces consumption
allows them to sustain themselves prior to
moulting into second instar nymphs when
food is not within the vicinity of their
harbourage site. As they grow into second
instar nymphs, improved foraging ability
allows them to fi nd a more balanced diet to
sustain development.
For horizontal transfer of insecticide to
have an impact on the population of
cockroaches, cockroaches that ingest toxic
baits must return to their harbourage to
distribute their toxic-laden faeces to other
healthy conspecifi cs. By analysing the
distribution of carcasses and faeces in a
test arena (117  15  15 cm) after cock-
roaches were baited with hydramethylnon,
Buczkowski et al . (2001) reported that
84.2% of poisoned carcasses were scattered