290 



THE AGRICULTURAL NEWS. 



September 16, 1911. 



of leaves, which are essential for the elaboration 

 of raw food material, from which the structure of the 

 plant must be built up, and which goes also to the for- 

 mation of seed and lint. Plants have great powers of 

 recuperation, and the loss of a portion of the leaves may 

 be (juickly remedied by the development of others — 

 a circumstance which, nevertheless, lowers the vitality 

 of the plant and makes it less able to endure further 

 untoward conditions. Insects that deposit their eggs 

 in the twigs of trees, which they girdle so that the 

 egg maybe carried to the ground embedded in the 

 tissue which shall furnish food for the larva and at the 

 ^ame time protept it from its enemies, are also to be 

 considered under this head. 



The kind of loss to the plant occasioned by the 

 feeding of scale insects, leaf-hoppers, plant lice, cotton 

 stainers and similar insects, is likewise of great impor- 

 tance when these insects are numerous, but it is often 

 not readily discovered on account of the minute size of 

 the insect. The observer also often fails to realize the 

 drain placed upon the resources of the plant because of 

 the abstraction of food by the enormous numbers of 

 small insects which can be accommodated on a very 

 small area of its surface. 



The loss of raw and elaborated food material 

 'deprives growing tissues of their nourishment, and often 

 results in checkiiig growth and producing deformities. 

 Discoloured and shrunken leaves often indicate an 

 attack of this nature, and long continued exhaustion of 

 the kind produces weak, under-sized plants, and 

 often even results in their death. The red maggot 

 lives near the delicate cambium and bast tissues 

 of cotton stems, feeding on the rich supply of 

 elaborated food, and at the same time causing 

 the death of the adjacent tissues. The long- horned 

 beetles, whose larvae live as bark borers in the trunks 

 of trees, exist under like conditions, and exert a similar 

 effect on the plants they attack. 



Injury of a direct nature to plants, from the weaken- 

 ing of the supporting tissues, is often very serious. Trees 

 aflfected by borersj cotton plants which have suffered from 

 severe attacks of red maggot, and plants which have lost 

 their roots from the action of insects, are rendered less 

 able to resist the force of the wind. They are broken 

 off or blown over, either losing a portion or all of their 

 foliage-bearing structure, or being uprooted. 



The power to reproduce possessed by plants is often 

 greatly lessened by the attacks of insects. The Hower- 

 tud maggot, by its attacks on the developing buds of 

 cotton plants, causes them to drop, thus preventing 



the formation of Mowers and seeds. The boll worm and 

 the corn ear worm tunnel into the bolls of cotton 

 and the ears of corn, destroying the developing seed: 

 and, in the case of corn, these insects further interfere 

 with the reproductive processes by devouring the silk 

 of the ear, thus preventing pollination. 



(train weevils and grain moths attack Indian corn 

 and Guinea corn, feeding on the embryo, and ren- 

 dering subsequent growth impossible; or devouring the 

 reserve food, and in this way weakening the seedling 

 which develops from the planted seed. 



Direct injury to plants also results from the 

 destruction of their organs by insects, so that the ordi- 

 nary physiological functions are prevented from being 

 performed. The feeding uf the root borer destro3's the 

 roots of the cane; this prevents the absorption of water 

 and mineral food constituents from the soil, and the 

 plant is injured, and may even die. Borers in the stem 

 cause injury to the woody tissue, stopping the ascent 

 of raw liquid food material, and to the soft bark tissues, 

 preventing the proper distribution of elaborated food 

 from the leaves to the growing cells. 



The leaf-blister mite causes deformities of the 

 leaves of cotton, which reduce in amount the elabo- 

 ration of the raw food material, and other blister-form- 

 ing and gall-forming insects produce deformities which 

 interfere with normal plant processes. Leaf miners, 

 which live in minute tunnels under the epidermis 

 of leaves, reduce the extent of the action of sunlight 

 on the underlying tissues. When, as a result of great 

 increase in the amount of epidermis separated from the 

 subjacent green tissue, an air space is formed, and 

 foreign matter, .composed of insect excrement and dust 

 accumulates, the function of the leaf is greatly im- 

 paired, and it often dies prematurely. 



The principal tbrm of indirect injury to plants by 

 insects is to be found in the invasion of fungoid or bac- 

 terial diseases, which take advantage of the punctures 

 made by sucking insects and the tunnels which are 

 excavated by boring insects, in gaining entrance to the 

 inner tissues. Plants are, in general, protected by an 

 epidermal covering, which varies in thickness and 

 ipiality according to the species and to the part of the 

 plant on which it occurs. When the epidermis is 

 punctured, the soft tissue is exposed, and there can be 

 uo doubt that an easy opportunity is offered for the 

 entrance of disease-producing organisms. The moth 

 borer, the .shot borer and the weevil borer of the sugar- 

 cane perforate the epidermis of the cane stalk, and it 



