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Basic Services and his staff some 1,008 manholes were treated on
three separate occasions.
To indicate the degree of infestation a test baiting of these
manholes was also effected. This showed that in 713 instances
there were no takes and in 100 manholes the baits were washed
away. However, in 195 cases there was evidence that there had
been uptake of baits by rats.
Warfarin Resistance
Anti-coagulant resistance in the common rat (but not, so far,
in the ship rat) has been acknowledged by the Ministry of Agriculture,
Fisheries and Food to exist in certain defined areas of
the country but, what is more important, is the Warfarin resistance
in mice which is much more diffuse. This resistance in the
house mouse now extends to South East England and includes,
in particular, the London area.
It would seem that resistance is inherited as a single, dominant,
autosomal gene and it is the use of anti-coagulant poisons which
has favoured the selective breeding of a rat which, in normal
circumstances, would be at a genetic disadvantage resulting from
its higher demand for Vitamin K and its slower rate of propagation.
This genetic change has presented a challenge to the rodent
control staff but because of the effectiveness of anti-coagulants
in rodent control over the past two decades, few alternative
satisfactory poisons have been developed. The situation has been
met by using substances such as the narcotic Alphachloralose
and various rodenticidal dusts. Acute poisons such as zinc phosphide
and arsenic have been used on a limited number of occasions
where it was considered there was no risk of danger to the
public.
The use of these alternative methods of control has however,
increased both the time required and the number of visits carried
out by the rodent control staff in order successfully to rid the
premises of infestations.
With the aid and co-operation of this Council's Rodent Control
Section, an attempt to produce a suitable alternative rodenticide
was undertaken by the Ministry of Agriculture, Fisheries
and Food in field trials held in the Borough during the year.
Results were disappointing but further trials with other rodenticides
are continuing.
Poisons, though useful on a short term basis, tend to lose their
effectiveness because immunity eventually develops. Long acting