134 Fii'st Report on Economic Zoology. 



Three or fom- broods may occur in tropical climates. It is known 

 under a variety of popular names, such as the Purple Scale and the 

 Oranire Mussel Scale. 



TREATMENT OF AFFECTED TeEES. 



There are two ways of treating scale-insect attack : — 



I. Spraying, with either paraffin emulsion or resin wash. 



II. The gas treatment. 



1. Spraying for scale attack. 



A. Paraffin emulsion. This is used to kill the larval scale 

 insects when they are crawling from beneath the scales and to 

 corrode the scales away. The time of migration of the larvae should 

 be noticed when this wash is used, and the wash applied when they 

 are crawling about, to do most good. But it has been found more or 

 less satisfactory at any time if applied on several occasions during 

 the year, best at intervals of two weeks. 



Paraffin emulsion is made as follows : — Mix equal portions of 

 soft soap dissolved in boiling water and paraffin, and then churn 

 them up by means of a force pump until a creamy emulsion is 

 produced. "When required for use mix with twenty times its bulk 

 of water. 



B. Eesin wasli. There are many recipes for this — the following 

 is a good one : — dissolve 1 lb. of caustic soda in 1 J gallons of soft 

 water, then dissolve 2 lbs. of resin and 1 lb, of tallow by moderate 

 heat, and as it is cooking stir in gradually 1 quart of the dissolved 

 caustic soda solution, and then add water until you have 22 pints of 

 liquid. This forms a thick brown soap which is sufficient for 44 

 gallons of wash ; it being added to the water and well stirred ; warm 

 water, if possible, should be employed. This should be applied before 

 the blossom bursts, but in bad attacks it may be used later as 

 it is well to clear out the scale, even at the loss of all that year's 

 crop, through destroying the blossom. 



2. Gas treatment. This is largely employed for scale in the 

 United States, the Cape of Good Hope, etc. The trees have to be 

 covered with a tent of gas-proof canvas ; the hydrocyanic acid gas is 

 generated by putting water and sulphuric acid in a saucer or jar 

 and then putting lumps of 60 per cent, grade cyanide of potassium 

 into the mixture. The fumes may be allowed to ascend for an 

 hour or more — evening or dull days are the best times to fumigate. 

 The slower the gas generates the better ; the greater the quantity of 



