222 SCIENCE AND FRUIT GROWING 



eggs, coinciding as it does with that of blossoming, presents 

 difficulties in applying any remedy just at the time when the 

 insect is most vulnerable. 



In preliminary laboratory experiments it was found impossible 

 to ascertain the damage done to the eggs by an insecticide, as 

 the change in appearance of the eggs when injured, was much 

 less marked than in the case of the mussel scale ; consequently, 

 the method of counting the hatchings after the twigs had been 

 treated and placed in covered jars, was adopted. The fertilisa- 

 tion of the eggs appears to be very complete, for in the absence 

 of treatment a 98 per cent, hatching was obtained. Treatment 

 with the alkaline winter wash containing 6 per cent, of solar 

 distillate, emulsified by means of copper sulphate (p. 161), proved 

 almost absolutely fatal (96 per cent, mortality), and the action 

 of it appeared to depend chiefly, though not entirely, on the 

 caustic soda contained in it, for a lime-sulphur-soda wash con- 

 taining the same amount of solar distillate caused a mortality 

 of only 39 per cent., which was not raised beyond 70 per cent, on 

 increasing the proportion of paraffin to as much as 12 per cent. 

 A mixed salt and caustic soda solution (10 and 2 per cent., respec- 

 tively) produced a satisfactory mortality of 90 per cent., and 

 salt alone gave one of 75 per cent. 



Compared with these promising results, the treatment of trees 

 in situ was disappointing, doubtless due to the difficulty, already 

 mentioned, of applying the washes satisfactorily to the parts 

 affected. None of the washes in question, after being applied 

 on March 12 to 21, caused any mortality of the eggs, except in 

 the case of the lime-sulphur-soda wash with 6 per cent, of solar 

 distillate added to it, and there a mortality of 20 per cent, was 

 recorded. 



Other experiments were conducted on the treatment of the 

 trees with a wash containing 20 per cent, of whiting and 2 per 

 cent, of salt, which had been recommended for the purpose. 1 

 No good results' followed the application of this, and the sub- 

 stitution of lime for whiting proved equally ineffective, at any 

 rate when applied as early as February 26 (X, 27). What role 

 the salt could play in such a wash is somewhat obscure, and 

 further attempts at Woburn to establish any effect from salt, 

 even at strengths of 5 and 10 per cent., either alone or in con- 

 junction with other insecticides, failed (X, 26). 



Treatment with lime-salt, it is stated, to be effective, should be 

 made not earlier than two weeks before the buds burst, and in that 



1 F. V. Theobald, S.E. Agric. Coll., Wye, 1907, 40. 



