Aedes vigilax in Fiji — Burnett 
393 
infection. One would expect a lower mortality 
if they were fed on an animal with fewer micro- 
filariae, but probably a high final infection rate. 
Few dissections of A. vigilax caught wild have 
been made, but in a series of 30 mosquitos 
from Raiwai village on the Suva peninsula, one 
mature larva of D. immitis was found. 
DISCUSSION 
It was most unexpected to find that A. vigilax 
was refractory to the development of Fijian 
filariae. The insects which reached Fiji are al- 
most certainly derived from Sydney or from 
New Caledonia because transport from other 
parts of the range of this species (Iyengar, 
1955) is very rare. Since A. vigilax from both 
these places is an exceedingly efficient vector 
of the New Caledonian strain, it is very prob- 
able that difference is not in the strain of mos- 
quito but in the strain of parasite, although both 
are nonperiodic. This could be confirmed if mos- 
quitos of known provenance were fed on a 
Fijian donor. 
The failure of A. vigilax to develop mature 
Fijian filarial larvae readily was a considerable 
relief because its habits differ completely from 
those of our four native vectors (Symes, 1955, 
1956) . If it were a vector it would be likely to 
increase the prevalence of filariasis in places 
where it is at present unimportant, while to 
control it would require special measures. The 
arrival of this pest has been beneficial in one 
way, for it has drawn public attention to the 
importance of excluding such immigrants and 
to the need to reconsider the efficacy of the 
measures in force and of their application in 
practice. 
There is little doubt that this was a new in- 
troduction. The only previous report of A. vigi- 
lax was Lever’s (1940), afterwards declared to 
be an error (Lever, 1945). Since then much 
work has been done on Fijian mosquitos (Amos, 
1947; Symes, 1955, 1956; Laird, 1956) with- 
out the detection of A. vigilax, and our regular 
surveys in south and east Viti Levu found none 
before the first outbreak. Introduction by ship 
appears less probable than by air because A. 
vigilax would not be at all likely to breed on a 
ship and is a strong-flying and active insect 
unlikely to remain on board as an adult for the 
several days required for its transport. Ships 
coming direct from any part of its range out- 
side the malarial zone are not subject to fumi- 
gation in Fiji, but the waterfronts of the two 
ports appear inhospitable to the insect. Frequent 
searches were made along the Suva waterfront 
but A. vigilax larvae were found only once, 
after the city had been invaded from the other 
side of the Suva peninsula. Only a few larvae 
were found and there was no recurrence. At 
Lautoka, although infestation has persisted on 
this side of the island, A. vigilax has not been 
found near the harbour. 
That the species is capable of being trans- 
ported by air was demonstrated by its recovery 
in August, 1958, from an aircraft at Nandi. Of 
the two air stations, Lauthala Bay normally of- 
fers the better facilities for the establishment of 
a mosquito with the requirements of A . vigilax. 
In addition there is a greater chance that an 
insect will escape from a flying boat than from 
a landplane before insecticidal treatment, be- 
cause it is necessary to open hatches for moor- 
ing the former before treatment can be carried 
out. However, very few aircraft land at Lauthala 
Bay from places within the known range of 
A. vigilax, whereas Nandi receives many sched- 
uled flights from such places. Opportunities for 
arrival at Nandi are not only frequent but the 
first reports of mosquitos that were probably 
A. vigilax came from the airport area during a 
period when conditions there were unusually 
suitable for the establishment of this species, 
suggesting that this was the place of arrival and 
that on this occasion the usual disinsectisation 
procedure proved inadequate. The mosquito, 
once established, presumably spread round the 
island from the edge of one mangrove swamp 
to another (see Fig. 1) until unusually favour- 
able conditions of tides and weather permitted 
simultaneous rapid multiplication to plague pro- 
portions over a large area. If this account is 
correct it emphasizes the importance of the 
unusual feature, the flooding, which provided 
a refuge and breeding place on arrival. Intro- 
duction of a pest to a new country by man- 
operated transport depends on a sequence of 
events — the pest must be present near its poten- 
tial vehicle, it must be able to enter and remain 
