404 SECTIONAL TRANSACTIONS.—D. 
(6) Search for outside parasite.—Investigations 1916-1918 showed many species of 
grass-feeding froghoppers in Central America each with very small range, but 
known parasites range from Mexico to Brazil. More recent investigations 
equally unsuccessful. More promising to go further afield, e.g. to Africa, but 
with native pest, old crop and continental fauna problem more. difficult. 
& 
Dr. Lu. Ltoyp.—The Passing of Insect-borne Diseases from Britain. 
Britain has suffered in the past from serious epidemics of bubonic plague, typhus, 
relapsing fever and malaria. There is nothing in the meteorological records to 
indicate that any graded climatic change is responsible for their more recent absence. 
Plague was dependent on insanitary habits in towns and fragile houses, which, 
respectively, afforded food and shelter to the black rat and allowed it to multiply 
greatly. With change in these conditions enforced by legislation the black rats 
were reduced in numbers and plague ceased. Rapid reduction in numbers of the 
human flea is still in progress. 
Typhus and relapsing fevers, the louse-borne diseases, had their foci especially in 
gaols and insanitary camps, and when these were reformed the continuance of these 
diseases was due to the vagabond class. Outbreaks followed especially on famines, 
and the ability of the British people in recent times to make up any deficiency of food 
by importation has been an important cause of their cessation. Social measures 
which have tended to reduce the condition of utter vagabondage have helped in this. 
Malaria was widespread in England and Scotland up to 1800, and since then in 
several outbreaks a tendency to restriction of its northerly range is noted. It is 
suggested that an old strain capable of transmission at a somewhat lower temperature 
than present-day strains has died out, probably owing to very cold years. Other 
factors which have or may have played a part in the reduction of malaria are better 
treatment of the disease, increased drainage through improved farming, possibly also 
a change in the feeding habits of Anopheles such as Hackett and Missiroli think has 
abolished malaria from parts of Italy. 
Dr. P. A. Buxton.—Studies in the Biology of Anopheles Mosquitoes. 
The control of malaria rests partly upon reduction in the number of Anopheles ; 
we no longer attempt to control all species indiscriminately, for, of the 130 species 
which inhabit the world, only about 30 are incriminated as carriers of the Plasmodium. 
Inasmuch as each species chooses a particular type of water as its breeding-place, 
the problem of control is narrowed. In selecting a place in which to lay eggs, the 
females of one or two species appear to be limited by factors which are easily 
perceived ; for instance, one species seems always to seek out cold waters, and a few 
select water which is very salt. But the behaviour of most of the species is very 
difficult to understand, and it seems to be influenced by several factors. The students 
of these problems work very much in the dark ; they observe that one species breeds 
in tiny trickles of water in jungles, and another in rice fields, But when they try to 
analyse this behaviour they can only hope to discover the determining factors by a 
hit-and-miss method ; they collect and tabulate a large amount of information about 
acidity, light, dissolved oxygen, nitrates, &c., and then endeavour to establish a 
correlation between the observed distribution of a species of Anopheles and one of 
these factors. 
The matter might be approached experimentally, eliminating all variables except 
one pair, and observing the female mosquitoes’ choice under these conditions. It 
is difficult to do this with Anopheles which is an intractable insect, but one can easily 
experiment with Aédes (Stegomyia) argenteus, a species of mosquito which lends itself 
to experimental study. It is possible that understanding of the behaviour of — 
Anopheles might come more rapidly if attention were first given to unravelling the 
factors which influence Aédes in choosing a place in which to lay eggs. 
Studies on the biology of Anopheles tend to narrow the problem of control by 
defining the objective. There is also the possibility, which has been discussed for 
many years, that if we possessed more detailed knowledge we might be able to alter 
the environment, rendering a particular breeding-place unattractive to a certain 
species of Anopheles. 
rer 
iattine 
