Sustainable Cockroach Management Using Insecticidal Baits: Formulations, Behavioural Responses and Issues - Urban Insect Pests: Sustainable Management Strategies - page 72

Horizontal transfer of toxicants relies on
intoxicated cockroaches contaminating
their aggregation site and the surrounding
environment with their bait-contaminated
appendages, excretion (vomitus and faeces)
and dead bodies (Fig. 5.2). Additional
healthy individuals are affected through
consumption of, or lethal contact with,
these contaminated materials (Durier and
Rivault, 2000c; Buczkowski et al ., 2001).
Some of the secondary effects may also help
transfer of toxicant to sedentary life stages
(young nymphs and gravid females) that do
not venture far for their resources. The
feasibility of horizontal transmission of bait
toxicants under fi eld conditions was
documented in an apartment infested with
B. germanica using bait containing hydra-
methylnon (Silverman and Bieman, 1996).
Secondary killing property of baits is there-
fore considered an important criterion for
the evaluation of baits (Jordan et al ., 2013).
Several mechanisms of horizontal
transfer of toxicant have been documented
and they are classifi ed on the basis of the
route of entry of the toxicant into healthy
cockroaches as described below.

microbes and their byproducts from donors
to recipients via ingestion of excreted faecal
materials (Bell et al ., 2007). Coprophagy
occurs in all life stages but is most prominent
in early instar nymphs (Silverman et al .,
1991; Kopanic et al ., 2001). Kopanic et al .
(2001) found that 90% of newly hatched
German cockroach nymphs could survive
for up to 10 days and maintain more than
70% survivorship for more than 14 days by
consuming adult faeces when food sources
were not available. In comparison, nymphs
without adult faeces available died 60-fold
faster than those given adult faeces.
Interestingly, 54.5% of fi rst instar nymphs
were able to successfully moult into second
instars when female faeces were provided
as a food source, whereas only 8% could do
so when fed with male faeces. In contrast,
second instar nymphs provided with adult
faeces survived only slightly longer than
those without access to faeces. These
fi ndings suggest that coprophagy is stage
specifi c and adaptive. Cockroaches are
known to defecate on their harbourage site
(Stejskal, 1997), which acts as an aggregation
pheromone and provides odour cues for
cockroaches during their homing trip
(Rivault and Durier, 2004). For newly
hatched nymphs, coprophagy reduces the
risk of long-range food searching when food
is not available in the immediate surround-
ings of the harbourage. At the same time,

Coprophagy

In cockroaches, coprophagy occurs to
transfer hindgut symbionts, nutrients, and

Dead

Emetophagy - Feed on
vomitus

Vomitus

Cadaver

Bait

Poisoned

Cannibalism - Feed on
cadaver of poisoned individuals

Faeces

Coprophagy - Feed
on faeces

Fig. 5.2. Mechanisms of horizontal transmission (coprophagy, emetophagy and cannibalism) of
insecticide baits in cockroaches (from Lee and Ng, 2009).