INSECTS 221 



sion, guidance hud been obtained from previous work carried 

 out on black currants in treating them for big bud (p. 217). 

 Immersion for 5 minutes at 125 or even 120 was found to be 

 less satisfactory so far as the subsequent behaviour of the trees 

 was concerned, as the vigour of their growth was thereby con- 

 siderably impaired; but a prolongation of the immersion to 

 15 minutes at 115, or to 20 minutes at 110, had no bad effect. 

 It would appear that any deleterious effect on the trees by heating 

 them, is simply a question of temperature, and that, provided 

 the critical temperature is not exceeded, the duration of the 

 heating is immaterial. 



An attempt was made to apply the heating treatment to trees 

 in situ, using a steam fire-engine for the purpose. The result was 

 not successful ; though the steam was at a pressure of 90 Ibs. to 

 the square inch, the temperature produced by it on the branches 

 was not above 90 F., and to obtain even that temperature on 

 all the branches would have involved a very prolonged operation. 



(2) APPLE SUCKER (Reports, VIII, 58 ; X, 26) 



The Apple Sucker (Psylla mali) lays its eggs singly on the young 

 shoots and spurs, chiefly around the leaf rings, amongst the 

 fine hairs of the shoots, and in the axils of the buds. They hatch 

 in April, and the insect then forces its way into the nearest 

 blossom- or leaf-bud. The buds thus attacked, either do not 

 expand, or, after expanding, wither, the leaves turning brown. 

 The insect becomes fully matured and winged in May or June, 

 and lays its eggs in September or October. Though there can 

 be no doubt but that much damage is done to apples by psylla, 

 there are grounds for questioning whether the insect is really 

 responsible for all the mischief attributed to it. The pest was 

 rife at Woburn in 1908, and the blossoming twigs were swarming 

 with the insects, yet it was difficult to find any trusses exhibit- 

 ing the shrivelled appearance characteristic of psylla injury; 

 moreover, many of the apple blossoms had been enclosed in bags 

 for the purpose of certain cross-fertilisation experiments, and 

 when these were eventually opened, abundance of psylla were 

 found in them 20 to 30 in one bag yet in every case the blossoms 

 had set well. 



The difficulty in treating trees for this insect lies in the position 

 which it takes up on the trees, for any effectual spraying of the 

 extremities of the branches is very difficult, and even if these are 

 thoroughly wetted by the spray-fluid, this runs off immediately 

 on to other parts of the tree ; also, the date of hatching of the 



