1910.] Distribution of the Large Larch Saw-fly. 985 



was found to be abundant and actively attacking caterpillars, 

 and it is believed that it is also present in the Welsh District, 

 together with other parasites hitherto undetermined. 



The chief hope of checking the depredations of the saw-fly 

 appears to be in encouraging the spread of its insect enemies. 



Distribution. — The saw-fly was first reported from the 

 Lake District in 1906, from Cemmaes in Wales in September, 

 1907, and from Sundrum, Ayr, in September, 1907. In the 

 first two cases the attack had already assumed considerable 

 proportions, but in the last only a single tree was found 

 with caterpillars on it. 



After the first inspection in Wales it was seen that the 

 insect was much more widely distributed than had been 

 previously suspected, and a more complete inspection was 

 made with the idea of mapping-out the extent of the country 

 infected. To do this, it was thought advisable to devise 

 some scale to show the intensity of the attack, and the 

 following was adopted : — 



Intensity I. (worst). — Some trees already dead, others with 

 crowns very thin and practically defoliated in mid-summer. 

 General appearance of trees moribund. Leading shoots have 

 been attacked. 



Intensity II. — No trees dead. Trees badly browned in 

 mid-summer. Few terminal shoots to lateral branches pro- 

 duced during current year, dwarf-shoots thereby stimulated to 

 growth with result that these new shoots have been utilised 

 for egg-laying by the saw-fly. 



Intensity III. — No trees dead, considerable numbers of the 

 terminal shoots of lateral branches have had eggs laid in 

 them. Little or no browning effect in mid-summer. 



Intensity IV. — No trees dead. Very few of the lateral 

 shoots show signs of attack. 



The scale is rough, and of course artificial, but it serves 

 to show the relative intensity of the distribution. Under this 

 scale, an attack of Intensity II. to III. begins to cause serious 

 loss of increment. Attacks of Intensity IV. have almost 

 invariably been overlooked by foresters not acquainted with 

 the insect. 



A glance at the map for Wales will show how wide the 

 distribution has become in a comparatively short time. The 



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