12 Annals Entomological Society of America [Vol. VIII, 
remains true that the land owner who may be sued for damages 
if he permits his horse to break into his neighbor’s garden is 
not even liable to reproof if he raises caterpillars in armies, 
Hessian flies in swarms, and hordes of chinch-bugs, to destroy 
his own crops and then to spread throughout his neighborhood 
as a general menace and calamity. 
And so I might go on to enlarge my list of things done and 
things remaining to be done in various other lines of effort 
and activity if we are to do all that is needed to make our ento- 
mology applicable, and to secure the application of it. But 
I have gone far enough to illustrate the fact that the useful 
things we know and those we still need to learn are practically 
all items in the physiology and ecology of our injurious species, 
and that the physiological items are of practical interest to us 
solely because of their ecological significance. Even the human 
factors of our economic problem are really ecological, for they 
have to do with the relations and interactions of men among 
themselves, as affected by the relations and interactions be- 
tween themselves and their insect enemies. 
If you ask me now whether we should be any nearer the 
practical control of our most dangerous and destructive insect 
pests 1f we had the details of their ecology well worked out, I 
shall have to answer that I do not know, any more than the 
entomologists who studied the habits and general ecology of 
mosquitoes foresaw the use of their observations as an indis- 
pensable link in the study and control of malarial disease—any 
more than Laveran knew when he found a blood parasite 
associated with malarial disease in man that the remaining 
links in the chain would presently be traced. 
We can have, in fact, no better illustration of the economic 
value of ecology than this subject of insect-borne disease, the 
one of its kind which by the joint labors of entomologists, 
parasitologists, physicians, legislators, and administrators has 
been brought to the point of a scientific and practical success, 
perhaps the most remarkable and the most nearly complete 
of any achievement of applied entomology. Let us make of 
this a sample and test of successful research, distinguishing 
the successive stages in the discovery of the nature of malarial 
disease and the modes and means of its propagation—the 
joint conquest, as Sir Ronald Ross remarks, of medicine and 
zoology fighting side by side. 
