198 FOREST ENTOMOLOGY. 



there is nothing left but an empty husk. The insects hatch out 

 freely in May and June, and no doubt the insect contains only a 

 single brood in the year. As the female flower or cone of the Douglas 

 fir is very open in the scales, the female insect can have no difficulty 

 in depositing an egg in each seed. 



Having regard to the recognised value of the Douglas fir as a tree, 

 and to the unrecognised value as a shade-bearer, it is imperative that 

 this insect should, as far as possible, be kept in check. There 

 is, of course, no way of dealing with the perfect insect in the open 

 wood, and therefore remedial measures must be taken with the seed. 

 Hence Dr MacDougall's remarks may be given in full : 



" The cones should be gathered as soon as ripe (the latter half of 

 October), and should at once be subjected to such treatment as will 

 permit of the seed being abstracted. This seed should without 

 delay be fumigated with bisulphide of carbon. The method is as 

 follows : 



" Place the material to be treated in an air-tight receptacle. Pour 

 the bisulphide of carbon into a saucer or saucers, or such shallow dish, 

 and lay these on the top of the material. Close the receptacle. The 

 bisulphide of carbon vaporises, and as its fumes are heavier than air, 

 they sink down through the material. The receptacle should be kept 

 closed for forty-eight hours. One ounce of bisulphide of carbon will 

 do for 100 lb. of seed, or one ounce for every 50 cubic feet of air- 

 space. The treatment should be administered in not too cold a 

 temperature. Bisulphide of carbon fumes, being poisonous, should 

 not be inhaled by the operator, nor should a light of any kind be 

 brought near. If it is desired to store the cones during winter or 

 longer, these must be similarly fumigated directly they are gathered. 



" The results to be looked for from fumigation are 



" 1st. The germinative capacity of such seeds as have not been 

 infested is not interfered with. 



" 2nd. In infested seed, where the larva? may not have made much 

 progress in the destruction of the reserve in the seed, the larva will 

 be killed, and the seed may germinate. 



" 3rd. In infested seeds, where the contents have been altogether 

 or much destroyed by the larvae, and which therefore would not have 

 germinated, the larvae will be killed, and the issue of the next year's 

 brood of adults prevented. 



