1 88 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



extension of time, it is not possible for the Board's Inspectors to 

 examine every larch plantation in Great Britain, and the Board 

 feel it incumbent on them to ask for the assistance of every person 

 interested in forestry in tracing the presence of the infestation. 

 The search may be conducted in two ways : — 



1. The actual insect may be looked for as (i) egg embedded 

 in the shoots of the tree, (2) caterpillar feeding on the green 

 needles, (3) cocoons lying in the ground or among the long grass, 

 (4) adult on the wing. 



2. The larch trees may be examined for signs of saw-fly 

 attack, even though no insect can be found. 



The caterpillars or larvae of the large larch saw-fly may be 

 first looked for towards the middle or end of June. In 1909 

 the first seen were not discovered till 4th July, but they were 

 evidently some days old, and the season was rather late. They 

 appear in considerable numbers on the lower branches of the 

 larch, generally towards the terminal shoots in which the eggs 

 are laid. As they grow older they advance towards the stem, 

 and eventually may be found wherever there are any needles. 

 Larvae begin to spin up their cocoons in July. In 1909 the last 

 caterpillar was seen on 31st August, but in other years they 

 might be found later. 



When very small they are not easily noticed, but they grow 

 rapidly, and when full-grown are about three-quarters of an inch 

 long, with round l?/ack heads, three pairs of d/ack thoracic legs, 

 and seven pairs of abdominal legs of a greyish green, the same 

 colour as the rest of the body. 



The caterpillars feed at first in clusters, but afterwards they 

 separate in search of food. They assume various characteristic 

 positions, a common one being with their "tail end" curled round 

 the shoot on which they are feeding. When disturbed they erect 

 the hind segments of the body over the front ones. The larvae 

 of the large larch saw-fly can be distinguished from other larvae 

 that may be found on the larch by the following characters : — ■ 



Mofh caterpillars. Nematus erichsoni. 



Legs never more than 16. The caterpillars have 20 



If they are geometer cater- legs. 



pillars they progress by a The mode of progression is 



looping or spanning movement continuous, 

 characteristic of this family. 



