Mosquitoes
Mosquitoes are found in every region
of the world except Antarctica. They breed in standing
water in diverse aquatic habitats including freshwater
(even if heavily polluted), saltwater marshes, brackish
water, and even water found in discarded containers
and old tires.
Both male and female mosquitoes feed
on flower or fruit nectar, but only female mosquitoes
bite; they require a blood meal every three to four
days for the protein necessary to produce eggs.
Mosquitoes can be divided into two
types: daytime and night time biters. Those mosquitoes
that transmit malaria and Japanese encephalitis bite
mostly at twilight or during the night. Mosquitoes that
transmit dengue and yellow fever, on the other hand,
are daytime biters.
Mosquitoes bite indoors as well as
outdoors so you need to prevent mosquitoes from gaining
entry into living and sleeping quarters and to eliminate
those that might already be there.
The same personal protection measures
that you use against mosquitoes will also protect you
against ticks and biting flies - insects that transmit
Lyme disease, tick-borne encephalitis, relapsing fever,
typhus, leishmaniasis, onchoerciasis, trypanosomiasis,
and several other tropical and infectious diseases.
You will want to avoid mosquitoes and
biting flies for another reason - insect bites, even
without the risk of disease can make you miserable.
Bites usually cause localized swelling and itching,
and certain bites, such as from march flies, horse flies
and black flies, are very painful. Bites can also become
secondarily infected, usually from excessive scratching.
WHY do they always bite
ME?
How many times have you or a friend
thought that you’re the only one at an evening
barbecue being bitten by mosquitoes? Many theories abound,
maybe you taste better, you’re more visible because
of your light-coloured clothing, or mosquitoes prefer
young blood, etc.
Largely, the victim is not actually being bitten more
than anyone else, but is allergic to the mosquito’s
saliva. However, there is evidence that some of us are
more attractive to mosquitoes than others. When an adult
female mosquito first emerges from her nursery, she
usually spends two days maturing before she gets hungry.
In some species, she doesn’t get hungry until
she has mated. Typically, a hungry female flies off
until it finds an “odour plume” emanating
from a host. The main odour followed by these mosquitoes
is carbon dioxide, which is in every breath we exhale.
Once the female mosquito is close to her prey, different
cues take over. She now responds to heat, following
the convection currents of warm air which rise from
our bodies. Finally, once the mosquito has located a
host that smells and looks right, there is the taste
test, which is where insect repellent comes in.
Other things that affect tastiness may be the age and
sex of the victim, and there is some evidence that we
all vary in palatability from one day to the next. Mossies
are also partial to lactic acid, produced by our muscles
when we exercise. Theoretically, a person who has just
finished a jog should be a sitting duck for hungry mosquitoes:
producing heaps of CO2 and sweat, lots of heat loss,
and plenty of lactic acid. So if you feel that you’re
the one who’s always being bitten, try a decoy
– take some of the heat off yourself by inviting
a sweaty jogger to your next barbecue!
Dr Jamie Seymour, James Cook University, Cairns
Repellents
for Bloodseeking Insects
Insect repellents
provide a means of protecting against many dangerous
and disease carrying insects. If properly used they
will greatly reduce the risk of infection from disease
and provide a high degree of personal comfort when exposed
to large numbers of bloodseeking insects.
Repellents affect
bloodseeking insects by disrupting their hostseeking
abilities.
Mosquitoes, for
instance, are attracted from up to 70 metres away by
several factors including body odour, exhaled carbon
dioxide and by radiated heat. The feeding urge is then
triggered when the insects sensors come within range
of the lactic acid on the skin.
Repellents act
to block the insect's sensors when it comes in close
proximity to the skin. The odour or smell of a repellent
plays no part in the repelling action. It is the vapour
put up by repellents, which have a distinctive molecular
shape, that block the insects receptors thereby inhibiting
feeding.
Which
Repellent is the Most Effective?
N,N Diethyl
Tolumaide (DEET) is internationally
recognised as the most outstanding, all purpose repellent
available. The New England Journal of Medicine refers
to DEET as the 'Gold Standard' of repellents.
Patented by the US Army in 1956 DEET is deemed the safest
and most effective out of over 30,000 chemicals tested
over an 18 year period and is the standard by which
other repellents are compared. Used by an estimated
200 million people a year around the world DEET is used
in both consumer and military grade repellents.
Why
repellents work
Repellents work
on spatial action. They place a vapour barrier between
the skin and bloodseeking insects. For this barrier
to be effective all exposed skin must be covered.
How
to Apply Repellents
Regardless of
the repellent's strength, to be effective all exposed
skin must be covered. The percentage of DEET in the
formula will determine the length of protection time.
How
Long Do Repellents Last?
The protection
time varies with the individual, the amount of sweating,
humidity in the air, avidity of the insects, percent
of DEET in the formula and other factors. Lab trials
indicate protection time can be reduced up to 4 times
if sweating is a factor.
What
Repellents to Use & When
Recent Technology
advances in repellent formulations now offer water resistance
and low odour yet contain high levels of DEET in the
formulation. The desired length of protection time will
determine the level of DEET to look for in a repellent.
The higher the level, the longer the protection time.
Safety
Information: Repellents & Children
Chemical repellents
are not recommended for use on infants. For toddlers
the guidelines indicate repellents should contain not
more than 7.5% DEET. According to the US EPA (1998)
100% DEET repellents can be safely used on children.
From the Queensland Institute
of Medical Research
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