298 TiisectichJeii 



to horticulturists to investigate these jH'oblems. The wetting of leaves 

 and plant-buds is one point ; the wetting or penetration of insects is 

 another ; the toxic action on insects is a third, and the last is to combine 

 the three together in efficient insecticides that really do kill the insect 

 every time and that cause a direct mortality of 100 per cent. In seeking 

 an insecticide for woolly aphis, I would first seek a solvent of its wax. 

 This is easy, but it is far from easy for instance with beech Coccus. In 

 seeking an insecticide for apple sucker we first sought one that would 

 wet apple buds. For mussel scale I would seek either a solvent of the 

 secretionary part of the scale, or a liquid that would penetrate under 

 the scale. These are protected insects, but what about naked insects 

 such as bugs, aphides and the like ; each has to be tackled individually. 

 So too for stomach poisons. We know that we want to wet the leaves 

 uniformily. Does lead arseniate and water wet well \ I think not. 

 In using lead chromate we add 25 % soft soap and 1-5 % of gelatine, 

 simply to secure wetting ; it is worth while as we use less liquid to get 

 good even wetting and no dripping. What will wet one plant's leaf 

 may not wet another. We know that for cabbages, for instance, but 

 it is a factor seldom taken into account except with cabbages. 



I hope I have shown that there is a field for research in this question. 

 I wish we could get a satisfactory basis of reason on which to proceed, 

 and not have to rely on empirical methods which really are not always 

 successful. And I am inclined to think that in England too much 

 reliance is placed on the tar and water principle to the detriment of the 

 estimation in which applied Entomology is held by horticulturists and 

 fruit growers. 



