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13
In regard to the treatment of sewers, Mr. Carter's report indicates that Sodium Fluoroacetate
is much more effective than Zinc Phosphide and that the very low level of infestation obtained
while the former poison was used cannot be maintained by the latter. It was expected that this
would prove to be the case but the experiment of going back to Zinc Phosphide for twelve months
was worth trying because it is a much less dangerous poison to handle.
Mr. Carter reports as follows: —
"Organisation and procedure during the year were similar to that of previous years, and in
compliance with the provisions of the Prevention of Damage by Pests Act, 1949, comprised
inspection of properties to ascertain the presence of rats and mice, treatment of any such
properties found to be infested, and periodical maintenance control measures for the destruction
of rats in the City sewers.
It has always been the policy to seek the co-operation of occupiers and owners of properties,
and the response to this approach has been satisfactory. No difficulty has arisen in which it has
been necessary to resort to statutory action to resolve the problem.
A major proportion of the work consisted of inspecting defined areas for the purpose of
instituting collective action. In instances of individual notification of infestation, or request
for assistance in control measures, the property adjoining was also inspected and combined action
taken where necessary.
On the survey side of the work, 4,282 occupancies and properties were inspected, the varying
types of properties ranging from blocks of offices, riverside food warehouses, catering establishments,
factories and shops, to domestic dwellings. The time expended in block inspection is very
considerable, and although often with negative result, it is necessary for the success of collective
action.
A total of 682 infestations of rats or mice were treated, and of this number 332 infestations
were notified by owners or occupiers, and 350 infestations were found as the result of inspection.
This total comprised 10 major and 169 minor infestations of rats, and 139 major and 364 minor
infestations of mice. The rat infestations were mainly of Ship rat (Black) nature. Treatment of
these infestations entailed 7,202 visits for operational purposes.
A minimum of 1,070 rats was destroyed as the result of poison control measures and 595
bodies were recovered. Trapping resulted in the destruction of 60 rats. The use of "Warfarin"
anti-coagulant rodenticide for the control of mice resulted in 1,540 bodies being found. No records
are available of the results obtained by Pest Control firms servicing premises periodically.
The downward trend of rat infestation manifest in recent years has continued and a further
decline in the number of infestations treated and numerical density of the same has been
experienced. There is a 50% reduction in major infestations (20 rats or over) and 27% reduction
in the minor classification. Infestation of common rat character in surface properties was
again on a minor scale and only five infestations were found and treated.
The gradual increase and wider distribution of mice infestation apparent in recent years
has continued, and as previously mentioned, 503 infestations were treated during the year, as
against 20 infestations in 1944. In reviewing this problem, the relationship of the reduction of
the rat population must be taken into consideration. It might well be that the balance of nature
has been upset and the absence of rats has provided the necessary facilities, and full scope for the
build-up of mice infestation. In many instances, premises treated several years ago for rats
have remained free of that type of infestation, but have since been subject to mice infestation in
varying degree.
By reason of their small size and feeding capacity as compared to rats, plus their smaller
range of activity from their nesting quarters, harbourage, both structural and incidental which
would not be conducive to the well being of rats, is often quite acceptable to mice. In addition,
the thoughtless disposal of food scraps, wrappers and fruit parings, by occupants of buildings
provide the necessary sustenance to support a colony of mice.
To illustrate further the decrease in rat infestation and relative rise in mice infestation, the
following summary is included as a useful record.
The estimation of the number of rats killed is based on the amount of poison bait consumed.
The calculation is, however, based on common rat extermination and as 90% of surface infestations
controlled were of Ship (Black) rat character, the total estimate is conservative and could
reasonably be increased by 25%, as this species, being much smaller and finer built, consequently
consumes less food, and a smaller quantity of poison bait constitutes a lethal dose. The total in
the bodies found column is the sum of those taken from premises by the operators and does not
include any subsequently found by occupiers consequent on the elimination of structural
harbourage or removal of incidental harbourage.