INSECTS being black with white patches on the dorsum, which patches seem to become larger as the age of the insect increases. The Haslemere district some years ago was under partial cultivation of the hop, and the aphis Phorodon humuli was plentiful in the local hop- gardens. This aphis and the less common P. galeopsidis, which feeds on the hemp-nettle, which is not like the hop a true nettle, is now known to deposit its ova in late autumn on the dead stools of the hop-vines, just above the surface of the soil or a few inches below it, and thus an an- swer is given to the question, what becomes of the living aphis when its natural food-plant has entirely disappeared ? The answer is also made more easy by what now appears to be a fact, that there is a migration from the hop to the sloe at certain seasons. The sloe of course is a persistent tree and not perennial like the hop. P. malaheb should be probably marked off as a synonym, if this fact of migration be admitted. P. galeopsidis is a distinct species. The natural checks to the increase of P. humuli are well known, principally through the agency of the larvae of voracious Cocinellidce and Syrphidce^ familiarly known to countrymen as hop-dogs. Horticulture. The peach and nectarine trees have each their aphis- pests ; the former particularly is infested by Myzus persicte and Rbopalosi- phum diantbi. The first aphis causes open bladders on the leaves, within which the insects hide ; the second rolls and crinkles the leaves, and finally changes their colour to dark brown. R. diantbi is one of the usual great pests of the greenhouse. Myzus cerasi is the common black aphis which destroys the crops of cherry orchards. It also swarms on the garden plum, which tree is further injured by the attacks of Aphis pruni and A. padi. The pest known as American blight is only too familiar and obvious to the apple-grower, by the white cotton-like tufts which hang to the branches and trunks of orchard-trees. Scbizoneura lanigera has both aerial and subterranean forms, somewhat similar to those we see in the great vine-pest of France, Phylloxera vastatrix. The ova have been discovered both on the branches and in the crevices of apple-bark both above and underground ; singularly the males are found mouthless and incapable of taking any nourishment. This blighting pest may be reduced by a copious spraying with weak solutions of calcium sulphide, obtained by boiling to- gether a mixture of sulphur and quicklime in water. This aphis must not be confounded with another species, Aphis malt, Kalt, which does not injure the trees so much and is not tomentose. Myzus ribis is common on both the red and the black currant bushes. It forms red or brown open tubercles on the leaves. The bright-coloured Aphis cucurbiti and the ubiquitous A. rapi vie with the ' red spider ' in trying the patience of the grower of melons, cucumbers and gourds. On passing to vegetable blights we find that through them the gardener is often not happy in successfully raising his crop. The leaves of the common kale and cabbage are frequently made hideous by the half- decaying masses of dead and dying individuals of A. brassicte. Sometimes the combined weight of these insects nearly equals the weight of the leaf 171
Page:VCH Surrey 1.djvu/213
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