View report page

The second stage of the series comprised four treatments during the period September, 1952,
and June, 1953. The number of entrances baited in each instance was approximately 315, and
the poison "takes" were consistently low. They were 13, 14, 16 and 11 respectively, and with
one exception Were in the ½ and ¼ category.
Following the fourth control and after a lapse of three weeks, 413 sewer entrances were
again test baited, and the recorded result was 23 "takes", the estimated amount taken being
71 ozs+.
The third stage comprised four treatments during the period September, 1953, and June, 1954,
and as in the previous year the "takes" were low, the recorded results being 21, 4, 5 and 4
respectively. The annual test baiting result, three weeks after the final poison control, was 26
"takes" out of 405 entrances baited. In this instance 101 lbs. of test bait was putdownand
approximately 82 ozs. + was taken.
So far, thirteen controls with "1080" had been applied, during the course of which 262
bodies were recovered from the base of the sewer shafts or in shallow flows close to the base.
This number does not include those found subsequently by the sewermen during their routine
duties along the lengths of sewers or in dead ends, and no doubt many bodies were washed
away in rapid flows.
From an analysis of the detailed records collated before and during these controls it did
appear that the combination of quarterly controls and sodium Fluoroacetate had produced the
results it was considered could be obtained, thereby justifying the use of this highly toxic poison
and the labour and care taken in its dispensing and application.
In view of the low level of infestation believed to have been obtained, it appeared to be
an excellent opportunity to ascertain, as far as possible, if this level could be maintained by
"direct" poisoning with Zinc Phosphide at a concentration of 10%.
Four such controls were applied during the period September, 1954, and June, 1955, and the
poison bait "takes" were 7, 22, 15 and 3 respectively. A similar test baiting to that applied
after the "1080" controls was carried out, and a total of 405 entrances were baited for three
days. The recorded result was 63 "takes" (33 complete, 5 x 19 x Vi and 6 x \ or less).
The test bait "take" subsequent to the final "1080" control was 26 "takes" (15 complete, 5 x
3 x Vi and 3 x \ or less). In this series of controls 35 bodies were recovered.
Analysis of the sector recordings and the overall result indicated that the previous low level
achieved had not been maintained. The upward trend and distribution indicated by the acceptance
of the non-poison test baits coincided with the observations of the sewermen, who had noticed an
increase in the number of rats seen during their routine duties in the sewers, between controls,
and in particular the last quarter. The low poison acceptance and increase in test "takes"
plus the visual evidence indicated the possibility that poisons prejudice had been produced by the
continued use of Zinc Phosphide at a 10% concentration.
Following this result, it was considered that a return to Sodium Fluoroacetate was desirable,
and during the period September, 1955 and June, 1956, three controls were "direct" poisoning
and the fourth a pre-bait control.
In the September control 397 entrances were poison baited, and after three days 38 "takes"
(1 complete, 9x !i and 28 x \ or less) were recorded, and 52 bodies were recovered. In the two
subsequent "direct" controls the "takes" were 12 and 10 respectively, and with two exceptions
these were in the '4 or less category. These controls produced 21 bodies.
For the final "1080" control it was decided to apply a pre-bait treatment on the 1—3 — 5
system, the final pre-bait acceptance result substituting for the annual test baiting. Thunderstorms
and prolonged rain made recording difficult. The pre-bait result was 49 "takes" (36 complete,
9 x and 4 x 14). Some of the "takes" recorded as complete were doubtful and could
have been washed away by charged up flows. The poison result was 25 "takes" (2 x Vi and 23 x
'» or less) and 10 bodies were recovered.
Having now carried out 21 treatments over a period of five years principally with "1080",
it was suggested that Fluoracetamide, technically known as "1081" might prove advantageous
as an alternative to "1080", and after discussion with Dr. E.F. Turtle and Dr. F.W. Hentley,
Scientific Officers, Ministry of Agriculture, Fisheries and Food, it was decided that four direct
controls be applied in a similar manner to the "1080" treatments, and the manufacturers kindly
undertook to supply the required quantity.
Chemically this poison is similar to "1080" but unlike the latter, which is an extremely
fine powder, is in crystal form, which increases the safety factor in dispensing. It is readily
soluble in water, odourless and said to be tasteless.
The median lethal dose (LD50) for Common rat is about 15 MG/LG of bodyweight as against
1 MG/KG for "1080" and is therefore about 15 times less lethal to rats. After a lethal dose the
speed of onset of warning symptoms is slower than Zinc Phosphide for which the LD50 is 40
MG/KG.
16.