AN ENCYCLOPAEDIA OF HORTICULTURE. 



185 



Insects continued. 



Two-winged Flies (Tachina and allied genera), or to certain 

 divisions of the Hymenoptera. In this latter order, some 

 groups, with very numerous kinds in each, are entirely, or 



FIG. 293. ICHNEUMON FLY. 



almost entirely, confined to parasitism (Ichneumons see 

 Fig. 293 and Chalcididce), and many species in the other 

 groups of the order are also parasites. In fact, it may 

 almost be said that there are few Insects which are 

 not preyed on by one or more (and frequently by many) 

 of these minute parasites. It is hardly in our power to do 

 anything directly to increase the numbers of these allies ; 

 but it is well to be able to recognise their general 

 appearance, and to refrain from killing them. 



In many cases, however, we must not trust to the 

 efforts of birds and Insects to limit the numbers of 

 our Insect foes. When their attacks are severe, it is 

 necessary to remove or to destroy them more rapidly than 

 can be done by natural agencies ; and, though the methods 

 employed must be varied to suit the special circumstances 

 that call for them, yet the same methods are largely ap- 

 plicable for the destruction of many kinds of Insects. A 

 few of the more generally useful may be mentioned here. 

 Tobacco smoke is very fatal to many of the hurtful 

 Insects, where these attack plants under cover, e.g., in 

 greenhouses. It is especially efficacious against Aphides. 

 Either strong coarse tobacco, or the paper in which it 

 has been wrapped, is burned in the place to be freed 

 from the foe ; the doors are all kept closed during the 

 operation, and for some time afterwards. Infusions of 

 tobacco, of Hellebore, or of other insecticides, are some- 

 times prepared, and are scattered over the plants by 

 means of a watering pot or syringe. These applica- 

 tions are usually very fatal to larvae feeding on such 

 parts of plants as allow of the solution being properly 

 applied to them, and they do not injure the host. Scale, 

 and other Insects that lie closely adherent to leaves or 

 branches, are seldom much affected by tobacco smoke, 

 and they are best removed by washing the parts with 

 water, or with solutions of soft soap or of poisonous sub- 

 stances ; and the efficacy of the applications is increased 

 by using a brush to put them on with. Several kinds 

 of injurious larvae are in the habit of living in groups, 

 in or under webs. These are easily cleared away 

 with the webs ; and the whole should be destroyed, by 

 burning or otherwise. Larvae living in the interior of 

 branches, or in galls, cannot be reached without remov- 

 ing the injured structures ; and this is also usually 

 the case with root-feeders. When a plant is withering 

 without any apparent cause, the removal of the earth 

 from its root will, at times, disclose the hidden larva that 

 has been feeding there. Sometimes, also, larvae feed at 

 night on the leaves, and during the day hide themselves 

 in the earth. Hence, the depredators can be detected 

 only at night, by the use of a lantern. Many Insect 

 larvae roll up a leaf, or spin together two or three leaves, 

 so as to form a protection for themselves against all 

 means of destruction save hand - picking ; but, fortu- 

 nately, such larvae are seldom fatal in their attacks ; 

 though, frequently, the plants become very unsightly 

 under them. Trees and shrubs are attacked in this 

 way more often than are herbaceous plants. A severe 

 shaking will often cause a large number of the larvse to 

 drop from their tubes, and to hang suspended in the air 

 by silken threads till the danger is past, when they 

 remount by their threads. If a sheet is spread below 



Vol. 11. 



Insects continued. 



the tree, they may be shaken on to it, and then readily 

 gathered to be destroyed. The mere shaking of the 

 plant is not enough. Many larvae (e.g., those of Gooseberry 

 Sawflies, of Winter Moth, &c., fall to the ground when 

 full fed, there to burrow in order to form cocoons, and 

 to become pupae, within a very little distance of the 

 surface of the ground. Soot, gas-lime, and other nauseous 

 materials are often spread on the soil around the stems 

 of trees and shrubs, to prevent the larvae from burrow- 

 ing in the immediate vicinity of the plants, and to de- 

 stroy them by the poisonous properties of the substances. 

 The pupae may be greatly lessened in number by paring 

 off and burning an inch or two of the surface soil in the 

 autumn or winter. Opening the soil with a hoe or a rake 

 is also useful, as it destroys some pupae at once, and ex- 

 poses others to the chance of being eaten by birds, and 

 to unfavourable conditions during the winter. The 

 females of some of the more hurtful Insects are wing- 

 less, or have wings so small as to be of little or 



FIG. 294. MALE, FEMALE, AND CATERPILLAR OP WINTER MOTH. 



use (as the Winter Moth, see Fig. 294) ; they must, 

 therefore, crawl up the plants on which they lay their 

 eggs; and their path may be barred by placing a ring 

 of any sticky substance on the soil around the base of 

 the stem, or around the stem itself. Tar, or mixtures of 

 tar with materials to prevent its drying quickly, have 

 been used with success to form such barriers. Other 

 methods of treatment, suitable to particular cases, will 

 be found referred to under the names of the various in- 

 sects. See also Insecticides. 



The class Insecta has been divided into certain great 

 groups, called " orders," by means of characters taken mostly 

 from the structure of the mouth and of the wings, and 

 from the kind of metamorphosis they pass through in 

 their growth. These orders are well distinguished from 

 one another, and there is usually not much difficulty in 

 determining the group to which any Insect belongs. 

 Some orders are of far greater importance to gardeners 

 than are others; and to them the following remarks are 

 confined. These orders are as follows; 



Coleoptera, or Beetles. These have the mouth formed 



2B 



