Page:VCH Surrey 1.djvu/214

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A HISTORY OF SURREY on which it feeds. A beneficent thunderstorm or the ravages of numerous lady-birds, lace-flies and small Hymenoptera, all by their several actions, reduce this exuberant insect-life to its proper dimensions. Several root- feeding aphides are found in our gardens, as A. subterranea, Scbizoneura fodiens, and Tychea pbaseoli on the French bean, but the injuries done bear no proportion to those done by aerial forms to the green leaves. Ornamental flowers. Although it cannot be said that every plant has its own special aphis ready to attack it, the appended list may point out the fact that so far as observation goes certain aphides are only to be found on particular plants and trees. Thus Rhopalosiphum nymphace is believed to be exclusively connected with the water-lily, which suffers much from its attacks ; Aphis opima seems truly to poison the sap of our greenhouse cineraria ; Callipterus castanea I have only found on the sweet chestnut ; Pteroc allis jugla ndicola only affects the walnut ; Chermes abietis only the spruce fir and C. laricis the larch. But it is highly probable that in many cases a stint of the natural food may cause a taste for a plant of quite a different family. There is no strict rule which can be followed in this respect. British aphides are found even to affect plants indigenous to the cultivated parts of India. Siphonophora pelargonii and S. rosce are the common pests of our geraniums and calceolarias ; Aphis papaveris blackens the stalks of our poppies ; Siphonophora rosce, S. rosarum and S. trirhoda encrust the soft shoots of our choice roses, besides which other species infest the columbine, honeysuckle and other ornamental flowering plants. Forest trees. Notwithstanding the astringency of the leaves of the English oak they form the food of at least five species of aphis, the most prevalent of which are Callipterus quercus and Thelaxes dryophila. The finely clouded membranous wings of Dryobius roboris and of D. croaticus will separate these species from the former ones. They are also remarkable for the fine purple-red stain they give to alcohol and to turpentine spirit when insects are soaked in them. Stomaphis quercus is an example of a dying-out or defunct species ; it is remarkable for its very long and ex- tended proboscis furnished with fine bristles, used for piercing the sap- wood of Quercus sessifolia. It is perhaps the largest aphis yet described, and is very rare. Specimens were captured by F. Walker about 1850 on some oaks near Weybridge, at Dulwich and also at Finchley. The linden or lime tree shelters very many thousands of Pterocallis tiliee under its leaves. These insects, common in Surrey, occur on the continent in such profusion, and eject from their nectaries such a quan- tity of honeydew, that Boussingault the French chemist stated that one sick tree alone will produce three kilograms of the sweet liquid, and Kaltenbach says that in Switzerland the traveller may trace this aphis by the viscid substance which it sheds on the ground. P. tiliee is the prey of numerous parasitic Hymenoptera, twenty or more individuals being sometimes contained in the body of a single specimen. Another species of this genus, P. fagi, forms small companies which make the common beech almost hoary with the cottony covering of their bodies. The 172