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A total of 616 infestations were treated, and these consisted of 50 major and 278 minor
infestations of rats, and 152 major and 136 minor infestations of mice. The work entailed 8,214
re-visits for operational purposes.
In the process of the treatments, 11,320 initial baiting points were selected, 48,783 prebaits,
and 5,149 poison baits were laid. These measures resulted in a minimum estimated kill of
2,877 rats and of this number, 1,237 bodies were recovered. Trapping was the means of destroying
514 rats, and added to those found as the result of poison, a total of 1,751 bodies were removed
from premises.
The use of the anti-coagulant Warfarin in the treatment of mice infestations appears to be
generally successful, and many difficult infestations of this nature were treated satisfactorily.
Altogether, 852 dead mice were found as the result of such treatment.
In 29 instances structural rat-proofing was carried out by the occupiers and in three instances
defective drainage resulting in rat infestation was remedied.
In assessing the results of this systematic work over a period of several years, a retrospect
of detailed records show that since January, 1944, a minimum of 58,720 rats are estimated to
have been destroyed, of which 20,154 bodies were recovered. The yearly figures show a steady
decline in the severity of infestations, and the numbers destroyed, and to the figures quoted must
also be added the results obtained by Pest Control undertakings, servicing premises periodically.
Many of the infestations treated during the year were of a minor nature, but nevertheless
important, and such infestations of Ship-rats character often entail more work than those of
severer nature. It does appear, however, that while the distribution remains the same the rat
population numerically is greatly reduced compared with several years ago. Owners and occupiers
have become more rat and mouse conscious, and generally welcome advice, and treatment of
infestations that would have been accepted as inevitable in the past.
Infestations of common rats were particularly few, and during the year only five such
infestations were found and treated. This is possibly due in no small measure to the systematic
periodical maintenance treatments carried out for the destruction of common rats in sewers.
Four treatments were applied during the year in the manner described at length in the
Annual Report, 1951. These were carried out in March, May, September and December. The
March treatment was the fourth and final in the series of direct poison controls with Sodium
Fluro-acetate "1080," and following discussions held with the Technical Officers, Infestation
Division, Ministry of Agriculture and Fisheries on the excellent results which appeared to have
been obtained, it was agreed to continue the treatments until March, 1954, when twelve controls
will have been completed.
In the case of the four treatments May, 1951—March, 1952, approximately 306 entrances of
a total of 427 were selected for baiting. This number comprised 225 entrances where prebait
"takes" were recorded during the December, 1950, treatment plus 81 entrances which
showed a negative result at that time, but where "takes" were recorded on either of the two
previous six-monthly treatments.
In the March control only 53 "takes" were recorded (1 complete 2X¾ , 6X½ and 44 X¼ or
less). Of the 44 x ¼ or less "takes" 20 were so small as to be hardly perceptable.
For the purposes of the fifth treatment in May it was decided to bait also the entrances not
previously treated. The inclusion of the additional entrances would, it was believed, supply
some information on the build-up or otherwise of rats in lengths of sewers not treated for 18
months. Altogether 424 entrances were baited and examination showed 3 X½, and 17 X¼ "takes"
a total of 20 only. This result was again satisfactory being a reduction of 33 "takes" on the
March control. An interesting feature of the treatment was that only 3 "takes" were obtained
from the additional 129 entrances baited.
The possibility of poison prejudice was visualised and in order to be reasonably satisfied on
this point, a test baiting of all entrances was applied after a lapse of three weeks. In the poison
controls, sausage rusk was used as the bait base, and to ensure there would not be bait prejudice
also, bread rusk moistened with water at equal parts by weight was used, each bait being 4 ozs.
A total of 417 entrances were test baited and the baits were left down for two days, when
examination showed 35 "takes" (7 full, 3 X ¾, 10 X ½ and 15 X ¼). As in the case of the poison
baits some of the ¼ "takes" were mere nibbles. Altogether 104 lbs. 4 ozs. of unpoisoned test bait
was put down and the amount taken was estimated to be 72 ozs. only. This result is a very
great reduction on the pre-bait recording of December, 1950, when 225 "takes" (185 full,
29 X ½ and 11 X ¼) were obtained. The amount then taken was 67 lbs.
The result of the September treatment was 13 "takes" only (1 X ½ and 12 X ¼ or less), and
that of the December treatment 14 "takes" (2 x ½ and 12 X ¼ or less).
The graph illustrates the breakdown of the pre-bait "takes" from December, 1943, to May,
1948, and then the rise in December, 1948, which was maintained for the next two years. In
May, 1951, the method of treatment was changed, direct poisoning with "1080" being introduced.
The result has been a rapid decline in the rat population of the sewers to a lower level than we
thought possible, and it seems probable that if we are permitted to continue to use "1080" this
low level can be maintained."