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Plum Tree Insects

The Plum Aphis (Aphis pruni) is exceedingly destructive. Multiplication takes place by millions, and the insects close up the pores of the leaves by their tenacious excretions and the mealy exudations from their bodies. By the constant irritation of their rostra [suckers] the leaves roll up, and under this cover from the weather both the winged and apterous forms live overspread by the mealy powder, which probably to them is a protection.

The wingless female bearing living young is of various tints, from green to slight olive-brown, with three faint green stripes on the abdomen, short olive-brown horns, and brown eyes; the winged viviparous female is apple-green, with head, horns, body between the wings, and feet, black.

The winged male is small, dingy ochreous, with the head, part of the body immediately behind it, some markings on the back, and the body feet, umber-brown; the fore wings are large and broad ; sometimes the insect is black. It has been found in November in company with the wingless egg-laying female, which is small, pale greenish yellow, and transparent; and usually shows the mature eggs within, which are ready for laying.

The Hop Aphis (Phorodon humuli) may also be found in great numbers on Plum and Damson trees, and trees or bushes of the Plum kind, as late as May or June (that is until it takes flight to the Hops) ; and it may be found again on the Plum trees in autumn. The two kinds are so much alike that they might be mistaken at a glance, but they may be readily distinguished, with the help of a magnifying glass, by the Plum Aphis - the Aphis pruni - never having the large frontal tubercles which are characteristic, together with the lowest joint of the horns being gibbous or toothed, of the Hop Aphis, - the Phorodon humuli. The difference in size of these very minute insects is indistinguishable by the naked eye.

Washes with a foundation of soft-soap are the most desirable, because they have the great advantage of sticking in some degree to the Aphides. When these insects (as before noted) are covered with a kind of mealy powder, many of the washes used simply run off them at once ; and unless the application sticks to them, so as to kill them, or is given so violently as to knock them from their position, the labour does little good.

Some kinds of Aphides hybernate, and of some we cannot be sure whether they do so or not; but in the case of the Aphis pruni I am not aware of there being any record of the Aphis living through the winter, and we know that the eggs are ready for laying in November.

Washings and syringings with soft-soap mixtures, with anything mixed with them that would coat the egg and poison the embryo, or poison the young Aphis when it hatched in spring, would be very serviceable. This course is recommended in German orchard treatment; and for these purposes, that is, to destroy Aphis eggs, or Aphides harbouring on the trunk or branches.

Where there is plentiful water supply at hand, and also means of throwing it with force, I have known much benefit come from sending even this, with no additions, strongly at the stems and branches; fairly "swilling" the tree down. Whether the quantity of water thus running down to the roots would be injurious in late autumn or winter would be a point for consideration, but at growing time it is beneficial, and, by means of a good strong current sent at the more solid parts of the tree, a most serviceable amount of clearing of spring insect vermin may be effected.