37
are quite efficacious in killing mosquitoes, if a sufficient quantity is used; and
their employment has the additional advantage of not being disliked by natives.
After a large number of houses in the bazaar and syce lines had been treated
in this way with a negative result, it became apparent that this part of the work
was unnecessary, and it was discontinued at the end of February. By the end
of this month all larvæ had been killed off within a radius of nearly two miles
from the outer limits of the area and I had convinced myself that no adult insects
were present in the houses. Throughout March no larvæ or adults were found
in any parts of the area.
Throughout the winter a few adults and larvæ of A . f u l i g i n o s u s
a n d a f e w
“ hybernating” larvæ ofA . c u l i c i f a c i e s
w e r e f o u n d i n t h e v i l l a g e o f,
K o r a 2 ½ m i l e s
from the area, and during March the number of A. fuliginosus adults and larvæ
in this village increased considerably. In April the first adult A. culicifacies
were noted in this village and soon afterwards the number of larvæ and adults of
this species increased considerably. In the area, however, none were found.
At the end of April it was noticed that larvæ of A. culicifacies were being
washed down into the area along the irrigation canals from places outside; and
it was evident that this was one way at least by which anopheles mosquitoes could
re-appear in the area. Soon afterwards the first adults of A. culicifaciesw e r e
found in the houses of the area, but up to May 15th a daily examination revealed
the presence of only a few adults which it was supposed had developed from
larvæ washed in by the irrigation canals. No larvæ of A. fuliginosus had been
detected anywhere in the area up to this time. On making the usual examination
of the harness-rooms on May 16th, however,I w a s s u r p r i s e d t o f i n d n u m e r o u s
adults of A. fuliginosus; on almost every saddle four or five specimens were
seen. On searching the bazaar the same condition was noted; almost every
house contained specimens of this species. As the majority of those caught
were full-grown females distended with eggs, it was evident that they were not
newly hatched; and as the nearest place where adult A. fuliginosus had been
previously found was the village of Kora, it must be assumed that they had
come into the area from this village, a distance of 2½ miles. This observation,
taken in conjunction with others made last year in the district round Lahore,
convinces me that at certain times of the year anopheles mosquitoes are able to
traverse comparatively long distances. This opinion also receives support from
the fact that the unusual prevalence of A. fuliginosus in the Royal Artillery lines
lasted only a few days. Within a week it was again impossible to find a single
specimen of this species in the houses of the area, and no trace of their passage
through the lines remained.
This direct flight over a comparatively long distance is, I think, quite distinct
from the third method by which anopheles mosquitoes reached the area in the
spring, viz., the gradual spreading of mosquitoes in all directions from an area in