35 



INJURIES AND APPEARANCE OF SLUGS. 



All kinds of willows, with the exception, perhaps, of the weeping 

 willow and species growing into tall trees, are injured by these slugs ; 

 the imported yellow or golden osier willows do not escape. Yet the 

 species and varieties of the white willow seem to be preferred, at least 

 they are first attacked if a variety of food is offered. Young poplars 

 growing in close proximity to the willows, were injured as well, and 

 only their older and harder leaves escaped. Such poplar leaves, fre- 

 quently utilized by the female saw-flies for oviposition, were not used 

 as food until the willow leaves became scarce and hunger forced the 

 slugs to search for other food plants allied to willow. Nor are eggs in- 

 serted into poplar leaves until willow leaves for this purpose are lack- 

 ing. The greatest damage is done to young plants, and this is one 

 redeeming character of this insect, as insecticides are much more read- 

 ily applied to them. 



The defoliation of the young willow plants is bad enough by itself, 

 and if repeated several times in the same season or in consecutive sea- 

 sons will no doubt kill them. But still another injury is inflicted which 

 renders such defoliated twigs useless as osier. Whenever the plant is 

 forced to produce a new set of foliage the new leaves do not simply 

 replace the lost ones, but grow from new side shoots, thus destroying 

 the usefulness of the original shoot, which for commercial' purposes 

 should be of uniform texture throughout its whole length. 



The first indication of the presence of these slugs on the willows is the 

 peculiar little blister like swellings seen upon the upper surface of the 

 leaves and which sometimes give them a wavy or crumpled appearance. 

 If an individual leaf is investigated these swellings are seen to be oc- 

 casioned by the oval, whitish eggs, which are partly inserted into the 

 under surface of the leaf-substance. As the eggs approach the time of 

 hatching black spots and streaks appear around them, which are the 

 efi'ects of the numerous wounds made upon the leaves. As soon as the 

 young slugs appear they commence to gnaw small holes, which soon in- 

 crease in size. The numerous slugs born in the same leaf feed usually 

 in close proximity to each other, but thej"^ can not, however, be called 

 gregarious. Their slimy black color and filthy moist excrement soon 

 reveal their presence. As they grow in size they devour the whole leaf 

 and soon denude the plant, leaving only the thicker portions of the 

 mid-ribs untouched. The slugs make no attempt whatever to hide, in 

 spite of their conspicuous markings, but are plainly visible everywhere. 

 They can always be distinguished by the peculiar curved position of 

 the posterior segments, which frequently bend away from their true legs 

 in the form of an interrogation mark. 



THE DIFFERENT STAGES. 



The Egg. — As in the great majority of saw-flies, the female of this 

 species is provided with two saws under the posterior part of the abdO' 



