\\ II. AwATi 2H7 



X. Insecticide Treatment. 



In the course of the investigation of the life-history of Psylla mali 

 it was found that the larvae are covered with waxy secretion. As 

 they secrete the waxy stuff the under surfaces of the leaves get soiled by 

 the wax and become impervious to water. The buds besides having 

 a waxy covering have also got minute hairs and other structures of their 

 own which make it more difficult for water to reach them. My task was 

 to find a fluid which would thoroughly saturate the bud leaves and so 

 reach the larvae. I have used different percentages of the soap (soft) 

 solution and found one per cent, of the soap solution satisfactory. 

 One per cent, means ten pounds of soap in 100 gallons of water. But 

 the soap solution by itself was not effective enough the kill the larvae. 

 It was tried on some apple trees with the result that 72 per cent, were 

 killed and the rest were healthy enough. The soap solution not only 

 saturates the bud leaves but it engulfs the larvae also, though in some 

 cases without killing them. The reason why 28 per cent, were living 

 seems to be that the soap solution is very effective if it dries instan- 

 taneously. By doing so it blocks the respiratory pores (stigmata) of 

 the insects, which are thus suffocated and killed. This means that the 

 soap solution will be more effective on leaves exposed to the wind and 

 the sun. But in the case of buds the leaves are not so exposed and larvae 

 in these buds do not run such risks as those on the open leaves. The 

 soap solution is not poisonous by itself, and if it does not dry up im- 

 mediately it is utterly ineffective, for the larvae can be happy in it and 

 crawl out of it before it dries up and their stigmata closed up once for 

 all. This would explain why such a large percentage was living with 

 the soap solution. As the soap solution was deficient by itself, I had 

 to seek some poisonous stuff which would facilitate the action of the 

 soap solution. The stuff had to be one of the wax solvents, and for this 

 purpose I used many things: 



(1) Petrol. (4) Acetone. 



(2) Kerosene. (5) Creosote. 



(3) Xylol. 



All these are more or less wax solvents. The last reagent proved 

 to be the best on trial and I have made use of it. These reagents do 

 not increase the surface tension lowered by the soap solution and they 

 are miscible with it. It must be remembered, however, that though 

 they are poisonous to the insects and wax solvents, they do a great deal 



