168 THE ESSEX NATURALIST.
and in order to accomplish this the practicability of destroying
its winter host was considered. Now, from the naturalists' point
of view, it would be a thousand pities if such a beautiful and
ornamental shrub, with its characteristic green bark, opposite
leaves and its axillary cymes of coral-red fruits brightening many
an Autumn hedgerow, were to disappear from our midst, for it
is already none too plentiful. At the same time the average loss
of sugar beet of over 1 ton per acre due to black aphis (as was
the case in 1938) cannot be permitted in war-time.
Briefly, the life-cycle of the black aphis is as follows :—It lays
its small black, shining winter eggs around the bases of the buds
and in the crevices of the bark of the Spindle tree, between the
end of September and the end of November. These remain
until the following April, when they hatch out as the bushes are
bursting into leaf, and give rise to wingless females which feed
on the lower sides of the Spindle leaves, causing them to curl
at the edges. These females produce parthenogenetically and
viviparously further young, and large colonies are soon built
up. In May winged females begin to be produced in the colonies,
and these are the Spring migrants which migrate from the winter
host to the summer hosts, chief of which are broad bean and
sugar beet—particularly the flowering heads of the latter. This
migration continues into June, and on their new host plant these
winged forms produce living young which are wingless. Repro-
duction continues at a rapid rate characteristic of aphid life and
well known to gardeners, some winged forms being born also
which find their way to other food plants and so increase the
area of infestation, causing considerable damage by the with-
drawal of sap and injury to the tissues of the lower surface of
the leaves, thus seriously checking the growth of the young plants
and scorching the leaves by the excretion of honey-dew from the
aphids. Sugar beet plants grown for seed are also severely
damaged at times, the seed being reduced in size and the yield
being reduced in bad attacks to only 25 per cent of normal. This
is particularly serious in view of the fact that most of our sugar-
beet seed supplies have now to come from our own fields, foreign
supplies being no longer obtainable.
In September some of the winged females return to their
Winter host, the Spindle tree, and give rise to wingless females
capable of laying eggs, in contrast to the viviparous young
produced throughout the Summer. Males are also now produced
on the Summer host for the first time in the life-cycle—winged
individuals which migrate to the winter hosts and fertilise the
egg-laying females, and so the winter eggs are laid on the Spindle
tree and the life-cycle thus completed.