48 Disease and Death of Trees — Generalities 



to dry up, and even large branches and entire trees can be 

 killed by tliese scale-insects if they are abundant. 



A very large number of insects coming from several of 

 the various orders, inhabit the foliage and smaller twigs in 

 their egg and larval stage and produce what is known as 

 galls, peculiar swellings, tumors, or malformations, often 

 highly colored. Especially the famih' of gall-flies, number- 

 ing some hundreds of species, inhabit largely the oaks, 

 producing all sorts of leaf -galls. Among these arc the galls of 

 commerce from which ink and gallic acid are manufactured. 

 The damage is too small to deserve much attention, but 

 where excessive, the leaves should be gathered while green 

 and burned, to get rid of the deformation. 



These swellings or malformations of twigs, buds and shoots 

 are often accompanied by a shortening of the annual growth 

 and a crow^ding of the foliage, forming what is known on 

 willows as the "willow rosette" and on pines or on spruces 

 as the "pine-apple." 



The saiv-jiies, similar to the gall-flies, lay their eggs in 

 the tissues of the leaf, but as they live in colonies and have 

 often two broods in a season and their larvae feed \'oraciously, 

 they are more injurious than the gall-flies and may, as in the 

 case of the larch and the pine saw-flies, cause widespread 

 havoc. The conifers suffer especially from these pests. 



With the family of beetles known as weevils we come to 

 the stem-boring insects. For, although some feed on the 

 foliage and puncture the bark, their worms or grubs inhabit 

 not only the fruit but also the young twigs; the beetle 

 with its long cylindrical snout perforating the bark and 

 depositing an egg in the hole, the larva developing from it, 

 burrowing beneath the bark, loosening it from the wood or 

 boring into the stem and destroying the wood. 



Bark-beetles, the "grubs" of which live under the bm' 



