. British journal of entomology and natural history. Natural history; Entomology. BR. J. ENT. NAT. HIST., 8: 1995 135. Fig. 6. The beech blight aphid, Prociphilus imbricator, Tunxis Forest Massachusetts. often seems to prefer thin-barked twigs and even leaves (Fig. 6). Dense colonies of this woolly aphid are quite spectacular, since their members respond to disturbance by waving their abdomens, which bear long tufts of the insects' waxy secretion. The feeding preferences of P. imbricator show that the age and thickness of bark, even on a thin-barked species like beech, affects food quality. If
. British journal of entomology and natural history. Natural history; Entomology. BR. J. ENT. NAT. HIST., 8: 1995 135. Fig. 6. The beech blight aphid, Prociphilus imbricator, Tunxis Forest Massachusetts. often seems to prefer thin-barked twigs and even leaves (Fig. 6). Dense colonies of this woolly aphid are quite spectacular, since their members respond to disturbance by waving their abdomens, which bear long tufts of the insects' waxy secretion. The feeding preferences of P. imbricator show that the age and thickness of bark, even on a thin-barked species like beech, affects food quality. If we look at tree species which normally develop a rhytidome, we tend to find bark-sucking insects largely confined to their twigs and small branches. Well known examples of such insects include the pine woolly aphid, Pineus pini (L.), and the large willow aphid, Tuberolachnus salignus (Gmelin) (Bevan, 1987). In the case of spruces, the periderm of the main stem tends to remain fairly thin until the tree has reached a considerable size, and thus allows feeding by the great black spruce bark aphid, Cinara piceae (Panz.). Among those sucking insects that can occur even on thick-barked stems, though only in fissures, is the oak scale or "pox", Kermes quercus (L.). The oak scale, whose waxy capsules are visible as small shiny spheres, is associated with a dieback of oak in some parts of Britain. The prevalence of this disorder in the Forest of Wyre in Worcestershire has given it the name "Wyre pox". Another well known scale insect that is seen on thick-barked trees is the horse chestnut scale, Pulvinaria regalis Canrard. Its hosts include several genera of broadleaved trees apart from Aesculus, these including Acer, and Tilia. The adult females of this insect are found on the main stem and large branches of the host, but this is merely their final resting place where they lay their eggs under a conspicuous waxy secretion. The immature stages feed in the crown of
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