2 20 TRANSACTIONS OF ROVAL SCOTTISH ARBORICULTURAL SOCIETY. 



23. The Larch Saw-Fly. 



By Ai.KX. Rai hAN, Honskeid Estate Office, I'itlocliry. 



This very injtiriotis insect has increased greatly in central 

 Perthshire this season. It was first observed on Bonskeid 

 estate about the end of July 1910, though to all appearance 

 it had been established there for at least one (or more) years. 



In 1 910 the writer tried experimenting on the larva? by 

 means of hellebore dusted on with a common gardener's puffer. 

 This proved quite effectual but was slow in action and rather 

 expensive, while owing to this experiment being tried, hand- 

 picking was not resorted to. By the middle of August the 

 larvffi came to maturity and dropped off, the last colony being 

 seen on the 20th of August. 



This was in a plantation of mixed European and Japanese 

 larch about 15 acres in extent, and eight and nine years 

 old. The soil was a poor dry gravel with herbage of rough 

 grass and heather. Previous to planting, the area had produced 

 a crop of birch. At the end of autumn a search was made 

 for cocoons, but without success, the herbage being too rough. 

 However, a strict watch was kept on the plantation last summer, 

 and the fly was seen in June, the first of the larvae appearing on 

 the 4th July. By the 15th July the larvae had become cjuite 

 numerous, and were found on larch trees, old and young alike, 

 on every part of the estate, even at an altitude of 1000 feet. 



On the 22nd July hand-picking was started, and thousands 

 of larvfe were gathered every day until the young plantation 

 had been completely gone over. Tiie larv;e were found to 

 be much more numerous where the plantation had a southern 

 aspect, in which situation the trees were thin on the ground 

 and not of luxuriant growth. On some of these trees as many 

 as seven colonies, in different stages of development, with from 

 twenty to thirty larvre in each colony, were found. In 19 10 

 it was hoped that the Japanese larch would be immune, but 

 when thin on the ground they were found to be as badly 

 affected as the European larch. 



A 2-year old plantation on a different part of the estate, 

 part pure Tyrolese larch and part larch and Scots fir mixed, 

 was also found to be badly affected and had to be hand-picked. 



