110 MASSACHUSETTS HORTICULTURAL SOCIETY. 



mations on their trees, on some of which I counted as many as ten 

 different tents. No doubt I shall have work to do in ray own 

 orchard this spring when the progenj'of ra}- neighbors' caterpillars 

 appear on my trees. 



It has been suggested that insects might be destroyed by intro- 

 ducing some infectious disease among them, and I cannot rid 

 myself of the conviction that, in time, we may learn how to do 

 this, but thus far we have nothing to offer that is of practical 

 value. There are, at times, great invasions of insects in certain 

 localities which last for a short time, when they disappear as 

 suddenly as they came. This disappearance is not unfrequentl}' 

 caused by some contagious disease, and it remains to be discov- 

 ered what the nature of that disease is, and whether it is possible 

 to preserve the germs in any simple way and communicate it to 

 other insects at the proper time. 



Insects differ so much in their habits that it is necessary to deal 

 with one species very differently from another. Some devour the 

 leaves of the plants ; others bore into their trunks, and still others 

 attack the plant below the surface of the ground. Some are noc- 

 turnal in their habits, concealing themselves during the daytime 

 and committing their ravages in the night, while others feed only 

 in the daytime. Some have their mouth-parts developed into a 

 tube which they thrust down through the epidermis of the leaf and 

 draw the sap from within, while others eat only the epidermis 

 itself. 



To combat these insects successful!}' and to use the insecti- 

 cides judiciously, we must take into account their habits and 

 modes of life. While a poisonous insecticide sprinkled over the 

 surface of the leaves would destroy the leaf-eating species, it would 

 probably have no effect on those that draw the sap from within 

 through their tubular mouth-parts, like the plant lice and the squash 

 bug. For these the best agents to use are those that affect the 

 respiratory organs, such as pyrethrum and kerosene emulsion. 



For all leaf-eating insects, such as canker worms, tent cater- 

 pillars, forest tent caterpillars, tussock moths, and a host of 

 others which attack our fruit and shade trees, as well as man}- of 

 our shrubs, one of the best and most effectual remedies is 

 to shower the trees with Paris green or London purple in water. 

 The method adopted by the fruit growers in the State of New 

 York is to put tiiree empty kerosene oil barrels, having a capacity 



