In the majority of cases, bat populations diminished during the 
first six months following the final spraying. On the other hand, 
the population of the control house remained about the same during 
the first six months increasing in the last six months, as also 
occurred in the unsuccessfully treated houses. Bats were almost com- 
pletely eliminated from seven out of the ten sprayed houses, while 
six of these remained comparatively free of bats for more than a 
year and. the remaining one for six months. The reasons for three 
houses retaining some population and then building up again during 
the breeding period have been attributed to the less residual B.H.C. 
treatment which also was not so effective in large roof spaces. It 
is interesting to note that the most successfully treated houses were 
sprayed with either D.D.T. alone or mixed with B.H.C, The apparent 
lack of success in house number 4 with D. D, T. is explained by the 
incomplete application of the insecticide, as this was the first house 
sprayed by the new technique, 
OTHER INVESTIGATIONS 
To test the effectiveness of the sprays and the method of appli- 
cation used in experiments 4 and 5, houses not previously sprayed and 
of contrasting structure were chosen in the immediate vicinity for 
experimentation. 
COCOA BOARD EXPERIMENTS 
House A, of 2,456 sq. ft., about one mile east of house number 1 
and of very different design, being a single story building with very 
spacious roof space, was sprayed with D.D.T. 50% wettable powder at 
the low rate on November 5, 1958. Once again the slow but effective 
killing action of this insecticide was demonstrated. A total of 
375 bats were destroyed in four weeks with over half of these dying 
in the first week and more than a third in the second, 
Houses B and C, about half a mile east of house number 1 and of 
identical construction to house A were checked for bat populations, at 
which time house B had an average number of 195 bats and house C had 
an average of 11 bats. 
On inquiring into the history of previous human occupants of 
house C, it was discovered that several applications of aldrin insecti- 
cide, closely related chemically to dieldrin, had been made in the 
past and could account for the low bat population. It was, therefore, 
decided to spray house B only, when the following results were obtained 
from the application of a mixture of D.D.T. and B.H.C, at the low rate 
on February 3, 1959 (Table VI). 
12 

