98 



Life-History. The moths fly in June and July ; the eggs 

 are laid in little heaps in cracks and crevices in the bark 

 generally very low down, but sometimes up to the height of a 

 man. The caterpillars on hatching feed at first below the 

 bark, but later they gnaw irregular ascending galleries in the 

 wood. In cases of overcrowding (and more than 100 cater- 

 pillars have been taken from one stem) some of the caterpillars 

 may leave the tree and bore into another. When full grown 

 the caterpillar pupates, and the .pupation stage lasts about a 

 month or on occasion somewhat longer. Before the emer- 

 gence of the moth the pupa pushes its way partly out of the 

 burrow in the tree and the empty pupal skin may be seen 

 projecting after the emergence of the moth. The cocoon has 

 been found projecting from the soil of a garden near an 

 infested balsam poplar. 



The life cycle appears to vary in length. A period of two 

 years is given by some authorities but the majority consider 

 that it extends to three years, and that under exceptional con- 

 ditions it may last for four or even five years. 



Methods of Control. (1) Trees which are badly attacked 

 and are of no great value should be cut down and the larv;i> 

 destroyed. 



(2) When a tree is only slightly attacked or when it is of 

 special value for shade or ornamental purposes, one of the 

 following methods may be employed: (a) Small quantities 

 of carbon bisulphide may be injected info the holes in the 

 trunk, (b) Small pieces of potassium or sodium cyanide may 

 be pushed into these holes. Whichever poison is used the 

 holes must be thoroughly blocked with clay immediately after 

 the operation. 



Injections of carbolic acid, paraffin, or a solution of nicotine 

 are also s-iid to have succeeded in certain cases, but either 

 cn.rbon bisulphide or one of the cyanides will be found most 

 effective. The latter substances must however be fcrealerl with 

 care, as carbon bisulnhide is exceedingly inflammable whilo 

 the cyanides are virulent poisons. 



(3) As a preventive against the eg-layin<r of the moth the 

 trunk of Hie tree. UP to a height of eic:ht feet, mav be pnintor? 

 with a mixture of chv, lime and soft soip or clay ;uid cow 

 Hung. The mixture should nlso cover any exposed roots n* the 

 base of the trunk and should be applied during the month of 

 Mnv. This measure is mainly of service in parks and gM-Vns 

 where a few trees are affected and it is desired to take every 

 precaution to prevent the insect from spreading. 



