FACTORS INFLUENCING INFECTION OF ANOPH¬ 
ELES WITH MALARIAL PARASITES 
By CLAY G. HUFF 
DEPARTMENT OF BACTERIOLOGY AND PARASITOLOGY, UNIVERSITY OF CHICAGO, CHICAGO, ILL. 
To be an effective transmitting host of 
malaria an anopheline must fulfill certain 
exacting requirements. Its choice of breed¬ 
ing place and its flight range must make 
it a frequenter of human habitations. It 
must breed in sufficiently large numbers 
to offset the natural hazards connected with 
the transmission of the malarial parasites. 
It must have the proper tropisms for bring¬ 
ing it to feed upon man. It must be sus¬ 
ceptible to the parasites ingested along 
with its blood meal. Its length of life 
must be sufficient to permit the complete 
development of the sporozoites, and it must 
live in an environment suitable to this de¬ 
velopment of the parasites. It will be con¬ 
venient to classify all of the factors which 
contribute to determining whether the 
anopheline will be an effective vector into 
two categories: (1) those responsible for 
bringing the mosquito to the act of ingesting 
the blood of malarial patients, and (2) those 
responsible for the successful completion 
of the extrinsic malarial life-cycle within 
the mosquito. Into the first category fall 
the many behavioristic characters of the 
mosquito conducive to the contacts between 
it and man necessary to successful trans¬ 
mission. Into the second category fall the 
physiological and environmental influences 
acting directly or indirectly upon the para¬ 
sites while they are within the mosquito. 
The following discussion will be concerned 
primarily with the second category of fac¬ 
tors, with only a brief consideration of the 
factors in the first category. Many of the 
factors responsible for bringing the mos¬ 
quito to and causing it to bite man will 
be adequately discussed by others in con¬ 
nection with other problems in malariology 
considered in this symposium. 
Without citing specific literature dealing 
with this first category of factors, many 
statements about them can be made almost 
axiomatically. It is well established that 
great differences do exist between species 
(and to a lesser extent between varieties 
or races of species) in respect to their 
choice of breeding places, the density of 
their breeding, the food preferences of the 
females, and the ability to withstand un¬ 
favorable environmental conditions. Ex¬ 
amples might be multiplied illustrating the 
importance of any of these factors or com¬ 
binations of them in making of a particular 
anopheline a dangerous vector, a less im¬ 
portant one, or an innocuous species. The 
chief concern, however, in this discussion 
will be with those factors which influence 
the infection of the anopheline, assuming 
that the latter has had a blood meal con¬ 
taining viable gametocytes. 
From the time that viable gametocytes 
are ingested by an anopheline mosquito 
until the moment of delivery of viable 
sporozoites to a new host a complicated 
sequence of events occurs. These events 
include very remarkable changes in the 
organism itself as well as migrations within 
the mosquito. It will be helpful to think 
of the factors which influence the develop¬ 
ment of the parasite—both intrinsic and 
extrinsic—as acting continuously upon the 
parasite throughout this period of develop¬ 
ment. 
It is desirable at this point to enumerate 
the more important events in the life cycle 
of the parasite within the mosquito in rela¬ 
tion to the possible effects of these intrinsic 
and extrinsic factors. Gametogenesis is the 
first important happening after the inges¬ 
tion of the parasites in the infected blood. 
Then comes fertilization of the macro¬ 
gametes. We shall soon review some of 
the factors which may influence these two 
processes. After fertilization of the macro- 
