PART 1V. ) 
fumigation, poisoning, or whatever may happen to be applicable to 
the particular case, to check its rapid spread to a disastrous extent. 
Often it is possible to effect a temporary check by such methods in a 
short space of time, without any very detailed knowledge of the 
bionomics of the insect. 
But the practice of Economic Entomology must not rest there. 
As soon as temporary relief has been obtained, if it can be obtained, 
from old and proved methods of artificial destruction, then is the time 
to tackle the problem seriously, and by detailed research into the 
insect’s bionomics, to discover whether there is not some reasonable 
hope of utilising one or more of the natural controlling agencies, 
which, aided perhaps in some way or other by the hand of man, may 
well prove more efficacious in eradicating the pest, than, for instance, 
the most efficient spray that can be imagined. 
Before proceeding to deal with the specific case of aided natural 
control which is the title of this paper, let us glance again at the four 
main causes which in nature keep the numbers of any given species of 
insect confined, in the main, within reasonable limits. 
(a) CLIMATE. 
That rain and drought, heat and cold, humidity and dryness of 
the atmosphere, have a marked effect on insect life is well known; but 
exactly what these effects are, and precisely what are the optimum 
climatic conditions for most prolific reproduction, is only imperfectly 
known for a very small number of insects. To some it may at first 
sight appear presumptous to talk of altering climatic conditions to 
the resulting disadvantage of an inseet pest; but though we cannot 
produce rain or a drought to order, we can increase or decrease the 
effects of either on an insect; though we cannot alter the direction of 
the wind by the fraction of a degree, we can control its force by the 
erection of wind-breaks; and most important of all, we can control 
within comparatively wide limits the conditions of temperature, 
humidity and evaporation actually occurring amongst a growing crop. 
Thus in a crop such as coffee, a little extra pruning will cause a freer 
circulation of air among the leaves, resulting in increased evaporation; 
a mulch on the surface of the soil will decrease the relative humidity, 
and a cover crop will increase it; shade will raise the mimimum 
temperature and lower the maximum, at the same time increasing to 
some extent the relative humidity; and the space between the plants 
has a very great bearing on the conditions obtaining in the field. But 
a great deal of bio-climatic research is necessary before much 
advantage can be reaped from the means which are at our disposal. 
Insects do not live in Stevenson meteorological screens, but in close 
contact with plants or the soil, consequently ordinary weather records 
are of little value, and it is absolutely necessary to determine the 
conditions in the actual places inhabited by the pests under 
investigation. 
It is hoped that the means will shortly be available to start some 
bio-climatic experiments in a coffee plantation in this neighbourhood. 
(b) Foop SuppLy. 
It is just because man plants hundreds of acres of a particular 
species of plant, and eliminates nearly or quite all the indigenous 
species from the area where he is growing that crop, that an insect 
which normally has to struggle for existence and is kept down in 
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