190 REPORT OF THE HARVARD AFRICAN EXPEDITION 
seasons of the year, insects are comparatively rare. Not many blood-sucking 
insects were encountered on the rivers or along river banks, — a scarcity in strik- 
ing contrast to the abundance of them found in certain other tropical countries, 
for example, along the Rio Negro and the Rio Branco in Brazil, where during 
many days clouds of simulium, S. amazonicum, inflicting troublesome and irri- 
tating bites are frequently met with. Mosquitoes although usually not unduly 
plentiful in Liberia either upon the coast or in most parts of the interior, are 
nevertheless not especially scarce, and, moreover commonly include such species 
as render them frequently dangerous to man. Eighteen species of mosquitoes 
were collected by Dr. Bequaert from Liberia and twenty-five from the Belgian 
Congo. The yellow fever mosquito, Aédes aegypti, is especially common in and 
about Monrovia, and is particularly abundant at the beginning and close of the 
rainy seasons, that is, from April to May and from October to November. In 
fact, at these seasons it may be the most common mosquito. This mosquito, and 
also particularly Anopheles and Culex fatigans, were found breeding in many parts 
of the town and in its outskirts, particularly in the water in the back yards of the 
houses, in the gutters, at the sides of the streets and in the wells or cisterns 
used for drinking water. Most of the wells are open, and almost every yard 
in Monrovia has one. Aédes was also found by Bequaert breeding in holes 
in fallen trees along the Du River in Liberia as far as some twenty miles inland. 
Obviously this mosquito is particularly dangerous potentially in such a com- 
munity as Monrovia, where cases of yellow fever among the general population 
are not likely to be detected or recognized and of course not screened. Only 
when some person of prominence in the community has fever and other symp- 
toms of the disease, is it at all likely for yellow fever to be considered. Bequaert 
agrees with Dyar in the opinion that Aédes aegypti probably originated in the 
Old World and was carried by ships from Africa to America. There are, for 
example, several species of Aédes of the subgenus Stegomyia in Africa (three in 
Liberia), whereas in America there is only one, Aédes aegypti. As might have 
been anticipated, other species of Aédes closely allied to A. aegypti have been 
shown recently by Bauer ' at Lagos, West Africa to be capable of transmitting 
yellow fever infection in monkeys. In earlier years, Marchoux and Simond,? 
who attempted to transmit the disease to man by means of other species of mos- 
quitoes, obtained only negative results. The five different species employed 
were Aédes scapularis, Aédes taeniorhynchus, Culex quinquefasciatus, Psorophora 
ciliata and Psorophora posticata. However, since it has been shown that Ma- 
cacus rhesus monkeys can be infected with yellow fever virus, more extensive 
experiments in transmission can now be carried out than formerly when man 
only was known to be the host. Bauer has recently made experiments in trans- 
mitting yellow fever with seven different species of mosquitoes besides A édes 
aegypti, viz., Aédes luteocephalus, Aédes apicoannulatus, Aédes apicoargenteus, 
Aédes longipalpis, Aédes welmani, Culex nebulosus, and Eretmopodites chrysogaster. 
The results are as follows: 
| Bauer: Amer. Jour. Trop. Med. (1928), VIII, 261, and Jour. A. M. A. (1928), XC, 2091. 
2 Marchoux and Simond: Ann. Inst. Pasteur (1906), XX, 16. 
