394 FOREST ENTOMOLOGY. 



creature as to prevent it giving birth to young we should be checking 

 the pest considerably. 



Insecticides are now employed with great success, especially in 

 horticulture ; but obviously they are more difficult to apply in for- 

 estry, particularly in the forest proper. It appears best, therefore, 

 to suggest remedies in a general way for the nursery and individual 

 or ornamental trees. 



In the nursery remedial insecticides may be classified under four 

 heads: (1) fumigation ; (2) dressing the soil; (3) spraying; (4) mis- 

 cellaneous. 



As regards fumigation, it may be done in an open shed when re- 

 moving from the nursery to the plantation, or when foreign plants 

 have been purchased, or with a costly preparation on groups or in- 

 dividual trees. 



As fumigation has not been adopted to any great extent in this 

 country, the following account of Mr Lounsbury, Government Ento- 

 mologist, Cape of Good Hope, 1 may be given : 



" Fumigation with hydrocyanic acid gas is applicable for the de- 

 struction of scale insects on citrus-trees, and to a large extent on other 

 trees. It is without doubt the most efficient remedy for this purpose 

 yet brought into practical use. The eggs of the insect do not suc- 

 cumb to the gas unless this is used at a much greater strength than 

 what is necessary to destroy the insects themselves. One treatment 

 suffices for the destruction of those species in which the young are 

 produced alive. Successive treatments at the ordinary strength are 

 necessary to destroy all stages of egg-laying species, but it is more 

 advisable to give several treatments at this strength than a single one 

 which would destroy the eggs, because of the liability of seriously in- 

 juring the trees in the latter case. 



" In general, the treatment consists in covering the trees with an 

 air-tight cloth made in the form of a tent or sheet. The gas is then 

 generated beneath this cover by acting on potassium cyanide with 

 sulphuric acid, the amounts of the chemicals used depending upon the 

 dimensions of the tree. The coverings are removed after the expir- 

 ation of half or three-quarters of an hour, by which time the gas is 

 largely spent. Great care must be taken in the use of the gas, as it 

 is highly poisonous not only to insects but also to the higher forms of 

 life. When proper precautions are taken, however, there need be no 

 1 Report for the year 1906, p. 130. 



