616 The Oyster-Shell Bark Scale. [Jan., 



moulted skin is not thrown aside, but remains to form part of 

 the shield or covering of the insect, this covering being greatly 

 added to and completed by secreted matter. This second 

 stage is a quiescent one, but the insect anchored by its mouth 

 parts continues to suck up the sap. It is important, from the 

 standpoint of treatment, to note that it is in this second 

 immature stage, complete by the autumn, that hibernation 

 takes place. 



About the beginning of the next April, the second stage 

 males pass into the pupal condition, and, after a pupal stage of 

 three weeks, the pupal skin is cast and, in suitable sunshiny 

 weather, the adult males emerge. This last cast skin is to be 

 found for a time at the hind end of the scale. Meanwhile the 

 second-stage females — not really differing much from the 

 future adult females — have accomplished their last moult 

 and become adult. The adult females are sought by the 

 male, and pairing takes place, followed later by the laying of 

 the eggs. 



Treatment. — (i) All young stock infested should, before 

 being sent out for planting, be fumigated with hydrocyanic 

 acid gas. The form in which Aspidiotus ostreceformis is found 

 on plants in winter is one to which this poisonous gas will 

 prove fatal. ' (See Leaflet No. 188.) 



(2) Infested plants, in the open, should be sprayed in winter 

 with the winter wash recommended in Leaflet No. 70.* A 

 strong paraffin emulsion would kill the scale insects if it reached 

 them. One would be guided by circumstances, noting whether 

 or no the trees had on them a growth of lichen or moss, and 

 remembering also that A . ostreczformis is a scale which sticks 

 very closely to the bark, and that the external layers of the 

 affected stem may, to some extent, protect the scale. 



R. Stewart MacDougall. 



* The wash given in the revised edition (which is about to be issued) is composed 

 of 2 gallons of paraffin, i| lb. of soft soap, 6 lb. of caustic soda, and 28 gallons of 

 water. The soft soap should first be dissolved in 1 gallon of boiling water and to 

 this the paraffin should be added and the mixture thoroughly churned until a cream- 

 like emulsion results. (The thorough churning is important). The 6 lb. of caustic 

 soda should then be dissolved in the remaining 27 gallons of water and the emulsion 

 added ; the whole being well churned. The soft soap and paraffin emulsion wil 

 keep satisfactorily for some time, but the complete mixture should be used at once. 



