ing remedies, the first thing to be considered is the nature of the attack, so that the most 

 appropriate remedies may be made use of. It will be found, upon examination, that all 

 injuries to vegetation by insects, conform to certain general plans in accordance with the 



Fig. 1. 



Fig. 2. 



We 



m 



form of the mouth parts of the attacking insects, and therefore all remedies must be 

 applied upon broad, general principles, dependent upon these structural characters. The 



mouth parts of insects are all made upon one or other 

 of two plans, they are either, 1, in the shape of jaws 

 (Fig. 2), by which the substance of their food is masti- 

 cated (Fig. 3) ; or 2. they form a hollow tube, by which 

 the food is sucked up in a liquid condition. (Fig. 4). 

 For insects of the first group, as a Colorado potato beetle, 

 a caterpillar, or a grasshopper, all that is necessary is to 

 to apply to the foliage which it is desired to protect, 

 some poisonous material which will not injure the plant, 

 but which, being consumed with the leaves, will destroy 

 the insects devouring them. Such a class of materials 

 we have in various compounds containing arsenic. The 

 best known of these is Paris green. For the second 

 group, in which the insects do not masticate their food, 

 such remedies would be useless, for the insects, having 

 their mouth parts in the form of a long, slender beak or 

 tube (Fig. 4), could pierce through these poisonous sub- 

 stances on the outside of their food, and extract the 

 juices upon which they subsist from below the surface. 

 Well known examples of this second group are the 

 mosquito and the plant-lice, or Aphides. For these and 

 similar insects it is necessary to make use of remedies 

 which do not require to be eaten but which act by mero 

 contact with their bodies, or by giving off some volatile 

 noxious principle. For this purpose, preparations of 

 useful, as well as the vegetable 



Fig 3. 



carbolic acid 



«oal oil or 



insecticide known as " insect powder," or pyrethrum. These 

 remedies which I have mentioned are active remedies ; but con- 

 trasted with these there is another class of equal importance, 

 which are called preventive remedies, by which steps are taken 

 to prevent anticipated attacks from taking place. Amongst 

 these the most important are the following : High culture, 

 by which a vigorous and healthy growth is promoted — a proper system of rotating 

 crops, by which insects attracted to a locality by a certain crop will not have 

 in that same locality two years running, the same plant to feed upon. Clean farm- 

 i 11 ?) by which all weeds and rubbish are prevented from accumulating. Changing the 



Fig, 



