Internal spraying was extremely difficult and sometimes impos- 
sible due to the following conditions: There was very little working 
space between the roof and the ceiling, making it impossible for a 
person to stand and sometimes even to enter; the risk to the operator 
of slipping off joists connecting the pressboard and falling through 
the ceiling; extremely high temperatures, over 100° F.; inaccessi- 
bility of areas where the roof meets the ceiling and corners as well 
as the high points at the gable ends; and hazard to the operator due 
to the toxic nature of the chemicals, 
However, outside application under the corrugations was con- 
sidered to be impractical because of the height of the buildings, the 
high winds experienced and the unsightly appearance left on the walls 
after spraying, although in one instance this was the only possible 
method. In practice, power-operated low-volume spraying or dusting 
was the easiest and safest to apply when the operator could discharge 
the insecticide in the form of an air-assisted blast away from him- 
self, which would penetrate to all parts of the roof space. This was 
done by either placing the nozzle through the trap door at each end when 
it was not necessary even to enter the roof space, or if there was only 
one entrance present, by operating the machine from the middle of the 
L towards the blind end and then from the trap door as in the first 
method. 
Unfortunately, the residue of the low-volume spray was not what 
was desired and after dusting by the same machines and smoke generation 
all failed to give the required deposit, a high-volume method of appli- 
cation had to be adopted. Hand-operated machines of the knapsack type 
proved too cumbersome for this purpose and eventually a hose line from 
a high-volume power—operated spraying machine proved satisfactory 
(Figure 2). The operator could move this from one end of the L to the 
other with ease and without discomfort from the spray fumes, A further 
refinement was possible by the high-volume method in that the spray 
could be seen to penetrate the corrugated and louvred openings, serving 
as a useful, guide to adequate application and also placing a deposit 
of the insecticide where it was most needed. It will be shown later 
how important the method of application is when the results are assessed, 
It might also be added that although the smoke generators were ignited 
with due consideration being given to wind direction and trap door exit, 
they were still found to be most hazardous under these conditions. 
PRINCIPAL INVESTIGATIONS 
Ten houses were treated and one remained untreated as the control 
in the main insecticide experiment. Choice of materials, quantities 
and dilutions were selected on a comparable cost basis and are shown in 
the tables relating to each experiment. Water was the only diluent used, 
