THE APHIS VASTATOR. 
141 
of the abdomen, and are hollow, containing a 
peculiar matter in the interior.* The winged 
insect has four wings, with which it is capable 
of flying great distances ; but in its final state 
it.is usually a lazy creature, and not very prone 
to fly far. The insects feed by thrusting their 
suctorial apparatus into the cellular tissue of 
the leaf of such plants as they attack. 
Curtis first named this insect the Aphis 
rapce, from its having been found to attack the 
turnip. This name Mr. Smee apologizes to 
entomologists for having changed to A. vastator, 
the destroyer, because, as he states, it feeds 
upon the turnip in common with other aphides, 
itself too attacking twenty or thirty different 
plants. 
Mr. Smee thus states the connexion between 
the insect and the disease : — The aphis vas- 
tator comes upon the potato plant in a winged 
state, and there brings forth its young alive. 
These generally prefer a large and rather de- 
bilitated leaf. After a short time the insect 
brings forth other young, which young them- 
selves reproduce without any connexion with 
the other sex ; and thus from a single speci- 
men a plant may be speedily covered with the 
insects. It has been proved by Reaumur that 
in five generations one aphis may be the pro- 
genitor of 5,904,900,000 descendants ; and it 
is supposed that in one year there may be 
twenty generations. I know no reason why 
the vastator should be less prolific than its 
congeners. The vastator begins at the larger 
leaves of the plant, which, after a short time, 
becoming injured by the abstraction of sap, die 
either partially or entirely. This is not going 
on in one plant alone ; it is generally progres- 
sing in every plant in the field at the same 
time, leaf by leaf all dying. Regarding the 
mode in which a whole field becomes attacked 
I may observe that the vastator is a sad rover. 
When the creature first appears he is to be found 
sparingly distributed over the larger leaves 
of the plant ; but when the greater part of the 
plant is destroyed, and the insect has multi- 
plied, great numbers may be found on a single 
leaf: they then become partially starved, enter 
into the pupa state, cast their skins, and 
emerge as winged insects, when they fly away 
and leave no trace behind them, save and ex- 
cept the destruction of the plant, and some few 
specimens which have been injured by ichneu- 
mons. This fact is exceedingly remarkable, 
for on watching a piece of land, I have found 
scarcely one of the insects to be left behind, 
the greater part having had their wings de- 
veloped, and flown away. I think that from 
the period of birth, it requires about a fort- 
night before the aphis obtains wings and flies 
* Aphides are considered to secrete honey-clew from 
these organs. — M. 
away. "When the vastator attacks the potato 
each leaf is separately destroyed, and the mis- 
chief may extend to the stalk and the root. 
The effect may be watched upon a sprig of potato 
placed in water. When the insect has damaged 
the leaf of the plant it is much influenced by 
wet weather ; a shower of rain will fill the 
stems with water ; and in consequence of the 
solid portionf having been taken away by the 
insect, the moisture cannot cause the rapid 
growth of the plant which should take place 
under such circumstances. The sap being thus 
in too fluid a condition acts prejudicially, and 
the plant rots at the collar, the under-ground 
stems, various parts of the upper stem, the 
leaves, the fruit. Sometimes when the plant 
is freed from its pest, it will send forth new 
roots to nourish the stem, and the haulm will 
thus retain much of its vigour. If, however, the 
plant has been once seriously damaged, it will 
perish without a second attack of the aphis. 
It is remarkable that even those tubers of 
diseased plants which appear sound in the 
first instance are very apt to become diseased 
upon keeping. Thus we may infer that every 
part of a diseased plant is diseased. As a 
consequence of the individuality of a plant 
being preserved and propagated from parent 
to offspring, a plant originally diseased will 
continue its disease in any new growth which 
originates from it; and thus it is impossible 
to tell for how long the disease may continue 
to show itself in the progeny of a plant once 
infected. The probability is that in time, if 
the original cause should not continue to act, 
the malady would be gradually annihilated. 
Such is an outline, .necessarily brief, of the 
connexion Mr. Smee traces between the aphides 
and the disease. The chief objection that has 
been raised against this view takes the broad 
ground that aphides cannot destroy healthy 
vegetation. This is, however, an untenable 
position. Gardeners, indeed, too well know 
the powers of these insects as regards their 
destructiveness of vegetables ; and which they 
appear to effect in the manner pointed out by 
Mr. Smee. It may be interesting to show how 
far this opinion is opposed to general evidence. 
To notice individual cases : — the hop-plant is 
seriously damaged by an aphis, sometimes so 
much so as to destroy the crop, and the season's 
growth. The field-bean is attacked and 
destroyed in a similar way by an aphis. 
Geraniums and other greenhouse plants suffer 
irreparable injury from the attacks of an aphis. 
The young shoots of fruit trees are destroyed 
by aphides. The recorded opinions on this 
subject are explicit: we may quote a few ex- 
amples : — MTntosh, after noticing their extra- 
t That is, the solid matters contained in the sap.— M. 
