160 Insect Pests. 



unsatisfactory unless we have only one variety of apple in a planta- 

 tion. Under such circumstances we may destroy very large numbers 

 by spraying with soft soap and quassia, if we do so when we find 

 them as shown in Fig. 133, namely, waiting outside the buds. Even 

 then not all will be destroyed, as even on the same tree they do not 

 all hatch in one day, or even in a week. 



The Duke of Bedford and Mr. Spencer Pickering (10) have found 

 great benefit from spraying with tobacco wash. 



The various statements made that certain washes will kill or 

 corrode away, etc., the eggs must be taken with caution. None that 

 I have tried have any appreciable effect in this direction, and the 

 careful experiments carried out by Mr. Furley in conjunction with 

 many Worcestershire growers show clearly that no washes have any 

 material effect in killing the eggs. Nor when we have considered 

 the structure of the Psylla ovum, do we think that this is likely to 

 take place, unless the wash is so caustic that the trees would be 

 killed. The various statements as to the mortality in the eggs 

 after spraying have been, of course, given in good faith, but the 

 investigators liave not apparently taken into account two factors : 

 first, as pointed out by Schmidberger in 1837, the ova will not hatch 

 on shoots cut off the trees unless they have been cut off a few days 

 only prior to normal hatching ; and, secondly, the number of old egg- 

 shells and normal infertile ova. 



In one batch of shoots sent me by j\lr. Furley from sprayed trees 

 some twelve Psylla hatched out of some hundreds of eggs, one might 

 have said the various washes had killed all the rest; unfortunately, 

 untreated twigs were sent and fewer hatched (as it happened) from 

 these than from those which had been sprayed, the reason being 

 that the eggs mostly lose their vitality when the life of the twig is 

 destroyed. Experimenters have also neglected the fact in their " egg- 

 counts" that many old egg-shells remain, and these are what they 

 have probably assumed the wash has destroyed. The old shells can 

 easily be told by being grey and have a ruptured shell. Other ova 

 will be noticed which look dull and sunken ; these latter are simply 

 infertile eggs. I have known as much as 80 per cent, of Psylla eggs 

 to be infertile. One can only repeat that growers are wasting time 

 in spraying with winter washes to corrode the eggs of these insects. 

 The only treatment found of any use in preventing the young from 

 entering the buds is spraying the trees with the thick lime, salt 

 and waterglass mixture {vide appendix). Mr. Howard Chapman 

 first called my attention to this, and was so confident of the good 

 done in his plantations that further experiments were conducted at 



