Fleas and Flea Management - Urban Insect Pests: Sustainable Management Strategies - page 90

on the faeces of the adult fl eas, which
consist of proteinaceous partly digested
blood. The larvae avoid the light and
actively move deep into dark crevices
within the host's sleeping area, into the
carpet or into crevices in the fl ooring. The
larvae go through three distinct instars,
each separated by a moult. Larval
development is restricted to protected
places where relative humidity is high
(Silverman et al. , 1981). Larvae are active
for around 8 to 30 days, depending on
temperature and food availability, before
constructing a cocoon.

egg to adult, while at 21C the equivalent
fi gure is about 120 days (Silverman et al. ,
1981).

Main human-biting fl eas

• Cat fl ea ( Ctenocephalides felis ): This
species has become the most common
fl ea in households around the world,
wherever cats or dogs are kept as pets, or
exist as feral cats. The cat fl ea will bite
humans but prefers to be associated with
cats, dogs, foxes and, to a lesser extent,
rodents. The adult fl ea has both genal
and pronotal combs.
• Dog fl ea ( Ctenocephalides canis ): This
fl ea is widespread outside of the tropics
but in many areas is believed to be less
common than the cat fl ea. It does bite
humans but is most common on dogs
and cats and also on other wild animals
such as foxes.
• Human fl ea ( Pulex irritans ): This species
is the original fl ea parasite of humans
and has a cosmopolitan distribution. It
formerly thrived where bedding was
infrequently changed and domestic
hygiene was minimal. It is occasionally
found on other domestic animals such as
cats and dogs, and on wild animals such
as foxes, but has a strong preference for
pigs, where large populations can
develop if left unchecked. P. irritans is
now rare in modern housing owing to
improved hygiene and housekeeping.
The adult fl ea lacks both pronotal and
genal combs (Fig. 6.2).
• Oriental rat fl ea ( Xenopsylla cheopis ):
This fl ea is found on rats and other
rodents, especially in warmer countries.
In temperate areas it seems to be largely
restricted to port areas. However, it read-
ily bites humans, hence its importance
as a vector of bubonic plague. The adult
fl ea lacks both pronotal and genal combs.
• Hen fl ea ( Ceratophyllus gallinae ): This
species does occur on poultry but is
more commonly found in the nests of a
wide range of wild songbirds. Humans
may be exposed to and be bitten by this
species when working with poultry,

Pupae

Fully grown larvae spin a silken cocoon in
which they pupate. The cocoon surface is
initially very sticky and so becomes covered
in grit, fi bres and other debris, so camou-
fl aging the cocoon. Shortly after the cocoon
is formed, the larva metamorphoses into a
pupa and the pupa then develops into an
adult after 7-10 days. The adult fl ea stays in
the security of the cocoon until it senses
that a host animal is nearby. At cooler
temperatures, fully formed fl eas can remain
in their cocoons for up to 12 months if no
hosts are detected in the vicinity. Fleas in
cocoons are largely protected from contact
insecticides (Rust and Reierson, 1989).
Emergence of the adult from the cocoon
is triggered by a number of stimuli including
elevated temperatures, vibrations, sound,
carbon dioxide or direct pressure on the
cocoon. Once the adult fl ea has sensed a
potential host nearby, emergence from the
cocoon can be complete within one minute.
The phenomenon of synchronized emer-
gence of fl eas from their cocoons is respon-
sible for cases of sudden but short-lived
outbreaks of fl ea biting, such as when a
family returns home from an extended
holiday, or when people enter empty build-
ings where cats had been living.
The rate of fl ea development is very
dependent on temperature. The cat fl ea
takes a minimum of about 22 days at 32C
and 75% relative humidity to develop from