483 



The latter feed on the juices of the inner tissues of the host- 

 plant. They are armed with a pointed tube-like beak, which they 

 thrust into the tissues of their host-plant, and suck out the sap. 



Of the biting or food-chewing insects, some are : 



(i.) Root-eaters ; such as the white worm of the cockchafer ; 



the larvae of the cicadae. 

 (2.) Others, bark-nibblers ; as certain kind of beetles and of 



weevils. 

 (3.) Some are leaf -eaters ; as slugs, caterpillars, saw-flies' 



larvae, the carpenter bee. 

 (4.) Others injure the bud, the blossom, or the fruit; as the 



strawberry weevil, the codlin moth. 



Of the sucking insects, in a like manner, some are : 



(i.) Root-sucking insects; as the woolly aphis and phylloxera 



of the vine. 

 (2.) Others, ordinary bark-sucking insects; as the mealy 



bugs. 



(3.) Some leaf and bud or fruit-sucking insects ; as the 

 rose and the orange aphis, the red and other scales, 

 and plant bugs. 



When fighting against biting insects, their food plant is best 

 coated with substances which will act as internal poisons ; whereas, 

 when directing the attack against sap-sucking insects, the treatment 

 must be such as hurts and kills by direct contact ; they are external 

 irritants, and act from the outside, either closing the breathing pores 

 or killing by irritation of the skin. 



To the first category belong the various combinations of 

 arsenic, and chief amongst them " Paris green," a chemical com- 

 bination of arsenic and copper. When unadulterated it contains 

 55 to 60 per cent, of arsenic. It is almost insoluble in water. It is 

 applied either 1st, dry in a state of impalpable powder, mixed in 

 the proportion of loz! of Paris green with 21bs. flour, slaked lime, 

 road-dust, or ashes ; 2nd, or in a liquid mixture in the proportion 

 of loz. in 10 gallons of water. It should not be used in con junction 

 with any acid substance which would dissolve the arsenic it contains 

 and make it caustic, but, on the contrary, it is always a good 

 plan to add to it a handful of lime, which has the property of 

 turning insoluble any trace of caustic arsenic it contains. Being a 

 heavy substance, it quickly settles to the- bottom of the pumping 

 tackle, and requires agitating. 



Other combinations of arsenic, such as London purple and 

 arsenic and soda solution, are also used ; but genuine and unadul- 

 terated Paris green is the best. A little glue or flour paste may be 

 added, to cause it to adhere better, especially to plants with glossy 



Hellebore, unlike the arsenites, which are mineral poisons, 

 is a vegetable poison, and is less dangerous. It is a powder made of 



