The life-history of the rose-aphis, small and familiar as is the insect
itself, forms one of the most marvellous and extraordinary chapters in
all the fairy tales of modern science. Nobody need wonder why the blight
attacks his roses so persistently when once he has learnt the unusual
provision for exceptional fertility in the reproduction of these insect
plagues. The whole story is too long to give at full length, but here is
a brief recapitulation of a year's generations of common aphides.
In the spring, the eggs of last year's crop, which have been laid by the
mothers in nooks and crannies out of reach of the frost, are quickened
into life by the first return of warm weather, and hatch out their brood
of insects. All this brood consists of imperfect females, without a
single male among them; and they all fasten at once upon the young buds
of their native bush, where they pass a sluggish and uneventful
existence in sucking up the juice from the veins on the one hand, and
secreting honey-dew upon the other. Four times they moult their skins,
these moults being in some respects analogous to the metamorphosis of
the caterpillar into chrysalis and butterfly. After the fourth moult,
the young aphides attain maturity; and then they give origin,
parthenogenetically, to a second brood, also of imperfect females, all
produced without any fathers. This second brood brings forth in like
manner a third generation, asexual, as before; and the same process is
repeated without intermission as long as the warm weather lasts.
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