Oct. 1, 1899.] THE TROPICAL 
might be pruned, dipped, and burned, and the stand- 
ing trees fumigated with gas. Modifications of the 
treatment will be required to suit particular cases. 
When a serious pest has onoe firmly and widely 
established itself, little hope can be entertained of 
exterminating it, though much may still be done to 
keep it in check. 
Where trees are large and more or less detached, 
as in orange groves, and the crop a valuable one, 
the gas treatment is again the most satisfactory 
one. Bat where the cultivation is denser, and the 
crop not so concentrated, spraying is found to be 
more practicable. 
The choice of the insecticide must be regulated 
by the Hature of the crop. Arsenious compounds 
cannot be safely applied to food crops — such as fruit 
and vegetables — during the cropping season. And 
they can on no account be recommended for such a 
product as tea, unless employed exclusively after 
pruning. For, however minute may be the actual 
amount of active poison deposited on a single leaf, 
when we consider that it takes some 4001b. of leaf 
to make sufficient tea to fill a chest, and that about 
3,000 of the green leaves go to the pound, or 1-.3,000 
leaves to a pound of the finished product, it is 
evident that the amount of poison in a single chest 
of tea might be considerable. And further, daring the 
processes of packing and transport, it is by no means 
improbable that this mineral poison — which would 
dry off in fine powder— might gravitate and become 
condensed towards the bottom of the chest, with 
dangerous results to the consumer. The dangermay 
be considered far-fetched ; but I think it should be 
lecognised. 
, For the above reasons no patent preparatious 
Bhonld be employed to any large ex'.ent, unless the 
ingredients are well known. Such mixtures, being 
designed for general use, may contain several dif- 
ferent poisons acting in different ways, either ex- 
ternally by contract, or internally through the ali- 
mentary system. The proprietors of patent intsecti- 
cides not unnaturally object to disclose their formulee, 
and put off any questions by asserting that the 
amount of active poison in the mixture is so very 
small as to be practically harmless. This may very 
well be true in most circumstances ; but, as shown 
above, in other cases the poison might become con- 
centrated into a small portion of the product. 
For other reason compounds that depend upon 
arsenic or other mineral poisons for their killing 
properties are of little use against Ooccidw. Insects 
that subsist upon the sap of the plants should be 
treated with insecticides that kill by contact, such 
as soap, petroleum, pyrethrnm, &c. Arsenic, which 
adheres to the surface of the plants, is useful only 
against pests such as caterpillars, grubs, and slugs, 
that take in solid food. Mr. Maskell puts the mat- 
ter concisely. He says : ' Whatever damage is done 
(by scale insects) is effected by the sucking of the 
juices of the plant through the rostrum (beak) of 
the insect. It follows from this that applications of 
any fluid to the tree externally, with the object of 
poisoning the insects in their feeding, would be use- 
less, as their food is drawn from beneath the 
surface.'* 
There are many substances fatal to insect life, 
but perfectly harmless to the higher animals, that 
may be safely used. A list of the principal inaecti- 
cidea, with directions for their preparation and 
application, is appended. (See pp. xxxi ef seq.)- 
The most suitable season for spraying is when 
the young larvae are hatching. They are then in 
the most unprotected condition. In temperate cli- 
mates this season varies with different species, and 
should be made the subject of careful observation. 
In tropical countries many species, and those na- 
turally the most pernicious, appear to produce a 
constant succession of broods throughout the year. 
To produce any permanent result, spraying must 
be very thorough. The success of the treatment 
depends upon the actual contract of the liquid with 
individual insects. Even when the work is done by 
* Neio Zealand Scale Jniects, p, 26, 
Aj&RICULTURIST, 233 
a trained man, it is practically impossible to secliro 
the destruction of every individual. The difficulty 
is greatly increased when the work has to be in- 
rusted to natives. In conducting the operation, the 
position of the insects upon the branches and foli- 
age must be carefully noted, and the nozzle of the 
machine manipulated accordingly, so as to throw 
the spray upwarts against the backs of the leaves, 
or downwards on to the upper surface, or horizontally 
against the stems and branches. 
A few words may be said as to the apparatus for 
spraying. This is not the place to advertise any 
particular make of machine ; but some general 
principles may be given to help the would-be pur- 
chaser iu his choice. 
Points to be considered iu the selection of a 
machine should be; — 
I. ^idaptabihty to Transport. — For ordinary use, 
where small trees only have to be treated, there is 
no form so convenient as the knapsack pump. This 
consists of a metal vessel that rests upon the back, 
and is supported by straps passing over the shoulders 
of the operator. The handle of the pump (in the 
best patterns) comes forward under the left aim, 
and is worked by the left hand, leaving the right 
hand free to direct the nozzle which is attached 
by flexible rubber tube. The vessel usually contains 
the pump cylinder, and space for about four gallons 
of liquid. Where a larger appp.ratus is required, a 
barrel pump may be used. In this form the pum- 
ping apparatus is fixed in a barrel to which handles 
are attached, so that the whole apparatus can be 
carried from place to place by two men. Where the 
land is flat the barrel, or a metal tank, may be 
mounted on wheels for transport : but it should be 
designed to that the vessel may be dismounted and 
carried by hand to such places as ai'e inaccessible 
to the wheeled vehicle. Where^the lay of land is 
suitable, and large trees have to be treated, a more 
powerful apparatus maTy be mounted on a cart, and 
drawn by horse or bullock power. In such cases 
two or more lines of hose and nozzles can be worked 
from the same tank. 
II. Strength. — The materials employed in the con- 
struction of the machine should be such as are not 
readily corroded by the mixtures used. Mr. Louns- 
bury, in his report for the year 1896,* gives the 
following very practical hints on§ this'subject : — 
' Iron is so quickly corroded by many of the com- 
mon insecticides and fungicides that pumps in which 
the working parts are of this metal are not de- 
sirable. These parts of the pumps should always be 
made of hard brass For the sake of economy, the 
bodies of most pumps are made of iron, but oven 
here the use of brass lends greater durability, and 
is an advantage which in the end will probably pay 
for the additional initial cost. Bod-like parts and 
thin handles of cast iron are objectionable because 
so easily fractured. Any parts of rubber are damaged 
by contact with paraifin. Ignorance of this fact 
has led to the ruin of a large number of Vermorel 
knapsack pumps, in which a circular rubber disc is 
used for the propulsion of the liquid. The paraffin 
causes the rubber to swell, and thus becomes use- 
less for its purpose. 
' Copper is the best metal for tanks in knapsack 
pumps, and attention should be paid to the thick- 
ness of this metal. Thin copper^ will rapidly ear 
through. Tanks of sheet iron or tin are soon ruined 
by contract with liquids containing copper com- 
pounds, such as Bordeaux mixture and Paris green, 
and these preparations are also injuriously affected. 
But even copper tanks are not suitable for use with 
all spraying mixtures, since this metal is acted up- 
on by the sulphur in such compounds as "eau grison " 
and lime-sulphur-salt mixture. In these cases, the 
sulphur leaves the lime, with which it had united 
during the process of cooking, and unites with the 
copper to form copper sulphide. This compound 
forms in a thick black layer over the copper, which, 
if it would remain intact, would preserve the metal 
* Report of the Government Entomologist for the 
Year 1896. Cape of Good Hope, pp. 139-140. 
