490 
tmf tropical agriculturist. 
[January i, 1891 
extract, diluted in water, one to thirty, was found 
somewhat useful. A paper on microsoopio nematode 
worms (Tylenohus and root Rail) is perfectly ap- 
palling. The remedies for this pest are also good 
remedies for other plant diseases, — lime, and 
muriates and sulphates of potash and ammonium. 
In California, the threatened destruction of the 
orchards by the cottony cushion scale {Icerya 
Pzr'cliasl) the worst of all the bug tribe, was averted 
by the importation from Australia and the breeding 
and spread of “ ladybirds ” (Vedalia cardinalis). 
This scale-feeding insect might be tried as a remedy 
for green bug on coffee? There is a native “lady- 
bird,” but we do not know if it is identical with the 
Australian species which the Californian orchardists 
have found so great a benefactor. The losses caused 
in the United States by insects which ravage crops 
have been reckoned at £60,000,000 to £80,000,000 
per annum 1 No wonder, therefore, if much capital, 
science and experiment have been devoted to the 
study of the life habits of the insects and the best 
means of extirpating them and of lessening their 
ravages, where extirpation is impossible. From an 
able paper by Professor Olliff, the New South 
Wales entomologist, I extract some valuable and 
suggestive passages : — 
When man came to till and to cultivate, many insects 
which naturally fed upon the plants he grew found 
abundance of food, and multiplied accordingly. It has 
thus come about that the cultivation in large areas 
of one particular kind of plant has resulted in an 
increase of particular pests. To illustrate my ueau- 
ing it is only necessary to instance the Cottony 
Cushion Scale (Icerya Purchasi, Mask,) of the orange, 
and the Hessian Fly (Cecidomyia destructor, Say) of 
the wheat, species which have caused immense havoc 
in America and in South Africa, where they have 
found abundance of food brought together by the 
orchardist and farmer. Apart from this inevitable in- 
crease of native or indigenous species, many others 
have been imported with plants and cuttings, and 
also in the ordinary course of commerce, from one 
country to another ; for it is well known that some 
of the most destructive insect pests of Australia have 
been introduced accidentally from Europe and America 
and similarly some English pests came from the East, 
and some American pests from Europe. In these 
matters, indeed, a fair exchange may be said to take 
place, for we are responsible for sending a very trouble- 
some creature in the shape of the Cottony Cushion 
Scale (Icerya Purchasi, Mask.) to our American cousins 
and to our brother colonists in South Africa. If we 
take only a casual glance at the destruction^ which 
occurs every year to our crops we shall perceive that 
if these ravages could be brought under control, by 
lessening the number of the injurious kinds whenever 
they appear in excess, the benefit would exceed any- 
thing of which we have any conception. 
Of the many substances and compounds used as in- 
sect destroyers, the following are the best known 
Lime, sulphur, soot, salt, wood-ashes, corrosive subli- 
mate, naphtha, naphthaline, turpentine, alum, carbolic 
acid, phenyl, cyanide of potassium, green vitriol, am- 
monia, alkalies, benzine, vinegar, sulphuric acid, blue 
vitriol (sulphate of copper), hot water, &c. Most of 
these may be successfully used for specific purposes 
either dry, in liquid, or in vapour ; but the three most 
useful insecticides of general application in use during 
the early days of economic entomology in America and 
np to within a few years, were undoubtedly tobacco, 
white hellebore, and soap. Tobacco water aud tobacco 
smoke have long been employed against Aphides and 
other delicate insects, and are most useful. A quite re- 
cent advance in its use is by vapourising. The vapour 
of nicotine is most effectual in de troyiug insects 
wherever it cm bo confined, as in greenhouses. Thus 
the boiling of tobacco in such a greenhouse is as ef- 
footnal as and less injurious to the plants than the 
iiM';r methods of syringing or of fumigation by burning. 
The vapour gradually arising from tobacco stems strewn 
on the ground aud regularly moistened is likewise ef- 
fectual. 
White hellebore, either in dry or in liquid, has long 
been one of the most satisfactory insecticides against 
Saw-fly larvse, otherwise known as false caterpillars; 
while syringing with soap-suds will kill some soft-bodied 
plant-destroyers, and when used as a paint on the 
trunks of trees is an excellent repellent against the 
parents of different borers. 
_ More important, however, than any of these insecti- 
cides are the three now most commonly used. They 
are— (1) arsenical compounds, (2) petroleum, and (3) 
pyrethrum. The flrst act through the stomach, and 
are effectual chiefly against mandibular insects, i. e,, 
those insects with biting mouths ; the second and 
third act by contact, and are therefore of more ge- 
neral application, affecting both those insects with 
mandibular or biting mouths and those with sucking or 
haustellate mouths. 
The use of arsenic as an insecticide in the field dates 
from the year 1871. At the rate of 50 grains of arse- 
niate of soda and 200 grains of dextrine dissolved in a 
gallon of water and this diluted at the rate of about an 
ounce to ten gallons of water, it furnishes one of the 
cheapest of insecticides at command, and various pa- 
tented combinations of it have been extensively sold 
and used. Again, one pound of arsenic and one pound 
of sal-soda boiled in one gallon of water till the arsenic 
is dissolved, and diluted at the rate of one quart to 
forty gallons of water is also a good formala. The 
chief merits of arsenic are cheapness and solubility. Its 
demerits are its white colour, which makes it liable to 
be mistaken for harmless substances of the same colour, 
and its tendency to burn the plant. Paris Green or 
Seheele’s Green has been more extensively used then 
any other arsenical compound, and is, on the whole, 
one of the most satisfactory insecticides. 
A refuse obtained in the manufacture of aniline dyes, 
and known as “ London Purple,” is the ^hird impor- 
tant arsenical compound. 
It is used with diluents, either wet or dry, in the 
same manner as Paris Green. For some insects ex- 
perience has shown it to be legs satisfactory than Paris 
Green ; for many others it is equally effective, and has 
the great advantage over Paris Green of being cheaper; 
of covering twice the ground, weight for weight ; of 
being more soluble, less poisonous, more adhesive, and 
permanent in its effects. 
The following receipt is recommended by Dr. Riley 
for certain pests, and other applications will suggest 
themselves : — Forty gallons of water, j to J lb. of Lon- 
don Purple (or | to I lb. of Paris Green ), three quarts 
of flour, [N. B,] the solid ingredients intimately mixed 
with the water by washing them through a strainer, 
sprayed upon the trees by means of a force-pump and 
nozzle, was found to effectively destroy web-worm. The 
effect of the poison is sometimes not observable until 
after three or four days. Care must therefore be taken 
not to overdo the spraying. 
Petroleum, in its various forms, has long' been 
recog’nised as one of the most effective icsecticides 
known, all oily substances being particularly deadly 
to insects. Unfortunately, they are also ii.jurious to 
plants, and they can then therefore only be applied 
after the discovery of suitable methods of diluting 
them so as to kill the insects without injury to the 
plants. Refined kerosene has been used to a limited ex- 
tent, by forcible attenuation in water and spray, 
while some plants withstand doses of the pure oil 
Of the various substances used in attempts to emulsify 
and mix kerosene with water, none are more satis- 
factory than soap and milk. An emulsion resembling 
butter can be pro luced in a few minutes by churning 
with a force-pnmp two parts of kerosene and one part 
of sour milk, or soap solution, in a pail; emulsions 
marie with soap solutions being generally found to 
be the more effective- The liquids should be at about 
blood heat. This emulsion may be diluted with from 
nine to fifty parts of water which should be thoroughly 
mixed with one part of the emulsion. 
The strength of the dilution must vary according 
to the nature of the insect to be dealt with, as 
well as to the nature of the plant; but, finely sprayed 
in twelve parts of the water to one of the emulsion 
it will kill moat insects without injury to the pluut. 
The ppraying should be done by a force-pump iluouj^h 
