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eggs. The great advantage of D.D.T. is that its lethal action
persists and any dormant bugs which later become active
or bugs which have hatched out from their eggs, will be
fatally poisoned when they cross the sprayed surface. The
lethal effect of D.D.T. will last for about two months and
during this time, under favourable conditions, every bug will
be destroyed.
During the week or two following the spraying, occupiers
may see a few bugs and may feel that the method has
failed. They must be re-assured on this point. In all cases
of severe infestation it is advisable to repeat the treatment
at an interval which varies according to the season. The
reason for this is that some of the eggs may not hatch out
for many months; well after the D.D.T. has lost its lethal
effects.
Fleas and Lice: These insects are usually eradicated
easily by ordinary cleanliness. However, in bad cases, the
D.D.T. spray has played a most useful part.
Cockroaches: These insects can be a most objectionable
pest in homes and Hats of all types. The D.D.T. spray is
useless against them but encouraging results have been obtained
by the use of 5% D.D.T. powder. This is spread
liberally at places over which the insects are likely to pass.
Once some of the powder has become adherent to the hairs
of the legs, poisoning will commence. It is usually possible
to eradicate the pest within a week—fewer and fewer insects
being seen each day.
Flies: D.D.T. solutions are very lethal to flies but cannot
play avery big part in their control in civil life. The spraying
of fly-proofed cookhouses and food stores was valuable
in military camps and could be used by the public, in particular
by establishments which handle food. It is almost
useless spraying a room with unprotected windows as flies
will enter, contaminate food, and die some hours later when
the damage has been done. Their proper control must remain
the correct disposal of garbage and the elimination of their
breeding nlaces.