222 NEW YORK STATE MUSEUM 



their sustenance between the upper and lower epidermis of one leaf, the 

 larvae tunneling apples and other fruits, or the borers in the trunks of trees, 

 The practical farmer or fruit grower soon learns that another class of 

 insects is not affected by such internal poisons as have been mentioned. 

 Each season several reports are received at my office stating that paris 

 green has no effect when sprayed on trees infested with aphids or plant 

 lice. The simple reason for this is, that these forms belong to a large 

 class known as sucking insects, because they extract the fluids upon 

 which they live through a delicate beak inserted into the tissues. Con- 

 sequently particles of internal poisons lying upon the surface of a food 

 plant have no effect, as the tip of the tiny beak is beneath the surface when 

 the insect draws its fill. It is not difficult to recognize these sucking 

 insects by their work, and one soon becomes familiar with their general 

 aspect. They never devour portions of plants. The most common 

 evidence of injury is the withering or wilting of either entire leaves or 

 limited portions. A small lens will readily show whether the injury is due 

 to a biting or sucking insect. Some of the more common species falling 

 in this latter class are all plant lice, scale insects and the larger forms 

 like the squash bug, the four-lined leaf bug and their allies. 



Operation of contact insecticides. As a rule it is best to protect 

 a plant by applying paris green or other poison to its foliage, provided 

 the insect is one that devours. Otherwise, recourse must be had to con- 

 tact insecticides, that is, to substances that will kill an insect when 

 brought into contact with it. None of those commonly used are so 

 deadly to insect life, that they will kill by simply touching the victim, at 

 a single point. They operate by closing or choking the breathing pores 

 or spiracles, along the sides of the caterpillar, or they may exert a para, 

 lyzing influence through these orifices. Therefore it will be seen at once 

 that success will be in proportion to the thoroughness with which the 

 treatment is performed. Insects not hit by the contact insecticide are 

 unharmed, those barely touched, if affected at all, may recover. Only 

 those well covered with the substance succumb. It is by no means easy to 

 secure the des'red results, even with the aid of a good spraying apparatus. 

 Some insects take flight so quickly that it is practically impossible to hit 

 many with a spray. Among these are the small leaf hoppers which are 

 sometimes very injurious to certain plants, and about the only way they 

 can be killed is by catching them on sticky fans or screens carried 

 between the rows. Many plant lice secrete a woolly substance which 

 serves to i)rotect them from the action of insecticides. The drop of 

 honey dew on the young pear psylla and the hard covering of many 

 scale insects serve the same purpose. I'he attacks of some plant lice 

 cause the leaves to curl and thus they are protected from deadly sprays. 



