. Manual of fruit insects. Fig. 172. — Old and recently set oyster-shell scales on willow. This oyster-shell scale has a wide range of food-plants. Itoften nearly covers the bark of the larger branches (Fig. 170),and even the twigs of apple and pear trees, and is often equally asnumerous on lilac bushes, willow, mountain ash and poplartrees. It may also attack quince, plum, raspberry, currant andfig among the fruits, and includes more than twenty-five shadetrees and shrubs in its list of host-plants. It infests trees of allsizes and ages, often killing young trees and severely injuringlarge on
. Manual of fruit insects. Fig. 172. — Old and recently set oyster-shell scales on willow. This oyster-shell scale has a wide range of food-plants. Itoften nearly covers the bark of the larger branches (Fig. 170),and even the twigs of apple and pear trees, and is often equally asnumerous on lilac bushes, willow, mountain ash and poplartrees. It may also attack quince, plum, raspberry, currant andfig among the fruits, and includes more than twenty-five shadetrees and shrubs in its list of host-plants. It infests trees of allsizes and ages, often killing young trees and severely injuringlarge ones. Orchards that are kept in a thrifty growing conditionand the trees not crowded rarely suffer serious injury from thisscale, but we have seen the lower limbs especially, and sometimesthe whole of large trees, killed by the insect where the trees werecrowded and neglected. Usually the bark of the tree only is APPLE INSECTS 175. Fig. 173. — Oyster-shell scales turned over to show eggs. infested, but occasionally a few of the scales develop on thefruit even in the North, where there is but a single generationannually. The oyster-shellscale is beset bymany natural ene-mies. Some of theladybird beetles, thetwice-stabbed lady-bird especially, de-vour many, and theeggs beneath thescales are preyedupon and often alarge proportion ofthem, 50 to 75 percent in some cases,eaten by a mite, Hemisarcopies coccisugus, in France, andin America by the larvae of at least five minute parasites,Aphelinus mytilaspidis, abnormis, and fuscipennis, Anaphesgracilis, and Chiloneurus diaspidinarum. These parasites emerge through pin-like holes in thescales and often a majority of thescales on a tree show these usually requires two of the para-sitic larvae to destroy all the eggsunder a scale, one larva often leavingfrom 2 to 20 eggs. A few birds, thebrown creeper, black-capped chicka-dee and white-breasted nuthatch, arealso
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