488 PREVENTION AND DESTEUCTION OK INSECT PESTS. 



quassia, put in the wash may be of value, but it is not essential for 

 killing the aphides. Soft-soap also adheres to the aphides' skin, 

 and is useful besides in fixing poisons on the insect and foliage. The 

 more soft-soap used, within certain limits, therefore, the better. 

 Certain substances, as paraffin and tobacco, corrode the skin of 

 aphides. Mites, on the other hand, breathe cutaneously, and 

 not through spiracles. 



On the head of an insect we Jict/ee observed, besides the mouth, two 

 hinds of eyes, simple and compound, and in front of the two large 

 compound eyes a pair of jointed horn-like processes, the "feelers" or 

 antenms. — What are these feelers for? They are sense organs: 

 whether they serve for one or two or more sensory functions 

 we do not know. One sense is certainly developed in them 

 — namely, "smell." The sense of smell may also be seated in 

 the jointed palpi attached to the two lower pairs of jaws. Insects 

 have the sense of smell very acutely developed : they are attracted 

 to their food-plant by its odour, both for feeding purposes and for 

 oviposition. Plant three beds of carrots in your garden some dis- 

 tance apart : sow one thinly, so that you have no necessity to thin 

 them out ; sow the other two in the ordinary way, and thin out 

 one of these, damaging the plants by bruising as you do so, and 

 leave the soil loose around the plants left in the ground ; thin out 

 the third bed in the same manner, but sprinkle over it, as you go 

 along, sand soaked in paraffin, so that the sand falls down and covers 

 in the spaces around the young carrots. You will find the middle 

 plot infested with "rust," the flies having been attracted by the 

 smell from the bruised carrots ; the dressed plot and plot one will be 

 practically clean, owing to the paraffin destroying the smell of the 

 plant in the one case, and no smell being released in the other. The 

 use of these deodorants is very important as a preventive of insect 

 ravages, both for dressing the seed and young plants. 



Thus from studying the structure of an insect we see that we 

 can fight them in three different ways — by poisoning, by asphyxiat- 

 ing, and by destroying the natural smell of the plant. The corrosive 

 action of certain substances must also be noted. 



T^e two means of checking insect ravages are by Prevention and 

 Remedies. — By prevention the appearance of any pest is forestalled, 

 by either making the surroundings unfit for them to live in, by the 

 winter destruction of the insects, by trapping, or by the use of 

 deodorants upon seeds and seedlings. In regard to the winter de- 

 struction, which is one of the most important features in prevention, 



