46 REPORT OX INJURIOUS INSECTS FOR 1907. 



affected, and they recommend that all freshly imported Cattleyas should 

 be carefully examined, and if found to be affected, cleaned and 

 fumigated. 



Badly affected plants should be burnt at once, and fumigation with 

 Hydrocyanic acid gas resorted to (see p. 56). The various advertised 

 nicotine fumigants, so largely used by gardeners, are unsatisfactory. 



THE YELLOW WOOD WASP. 



Sir ex gigas, Linn. 



Not for many years past has this insect been so plentiful, and 

 numerous examples have been received for identification, as well as 

 damaged pieces of Firs, etc. 



The female deposits her eggs in holes bored in the Fir or Spruce ; 

 and the larvae eat out a curved tunnel in the softer layers of the wood. 

 They hibernate in these tunnels during the winter ; and in the follo\v- 

 ing year make their way into the deeper layers, and to the heart of the 

 tree. The second winter is also spent in these tunnels, and early in the 

 summer of the third year they pass to the open end of the tunnels, form 

 a pupal chamber, which they line with a glazed coating, and there 

 pupate. 



The perfect insects emerge in July and August, either by one of the 

 larval tunnels, or by boring a short passage through the wood. 



PREVENTIVE MEASURES. 



All coniferous timber that is weakly or damaged should be removed 

 from the forest, etc. 



Stumps, broken w r ood, and felled trees should not be allowed to 

 remain. 



Badly attacked trees are best cut and burnt early in the year. 



THE PEAR SAWFLY. 



Tenthredo cerasi, Linn. 



A Staffordshire correspondent reported a serious attack of this 

 pest in August last on pear trees. 



LlFE-HlSTORY. 



The flies appear in July, and the female lays her eggs on the upper 

 side of the leaves of the pear and cherry. The larvae hatch out in 

 a few days, and feed upon the upper surface of the leaves. The familiar 

 name of slug-worm, so often applied to the caterpillar stage, is very 

 suitable. They are a dark green in colour, broadest at the head end 

 and almost perfectly smooth. They possess ten pairs of feet. In four 

 to six weeks they become full-fed, and cast their skins. They are then 



