80 STATE HORTICULTURAL SOCIETY. 



that is such a nuisance among greenhouse, plants shows a preference for one- 

 plant over another. It will not trouble the common Zonale Geranium, the 

 Coleus or the Chinese Primrose so long as there are sufficient plants for its use 

 of Cineraria, Achyranthus, or fancy Pelargonium. Perhaps this peculiar habit 

 of the greenhouse Aphis may be attributed to the fact that in the greenhouse,- 

 having better external requirements for generation, more tender and succulent 

 plants to prey upon, and fewer insect enemies to contend with, they have grad- 

 ually acquired a taste for the great variety of house plants upon which we now 

 find them. 



But the main questions of interest to the horticulturist concerning these 

 plant pests are, in what way do they injure the plants, and how can they be 

 most effectually destroyed. To answer these questions intelligently we must 

 understand the structure and habits of the Aphis, and have a knowledge of the 

 insecticides that have proved of practical value — what they are and how 

 applied. 



As previously stated, the Aplrs or plant louse is an insect. What is an 

 insect? 



One great natural branch of animal creation is known as arthropoda, because 

 all animals which it includes have jointed bodies, jointed mouth-parts, jointed 

 legs, and other jointed appendages — the term arthropoda literally meaning 

 joint-foot. Under this branch there are two classes — Crustacea, including 

 crabs, lobsters, and similar jointed aquatic animals which get oxygen by means 

 of trachea, as in true in sec s, or little sacs as in spiders. Any creature hav- 

 ing jointed bodies and appendages, and breathing air by means of trachea, as a 

 wasp, fly, beetle, or plant louse, belongs to the class insecta, and is called an 

 insect. As already intimated, the genus Aphis belongs to the oraer Hemiptera. 



This order is easily recognized by its hostellate mouth-parts, four wings, and 

 imperfect transformations. All the Aphides are quite small, most of the 

 species being less than an eighth of an inch in length. Some are semi-globu- 

 lar in form; some oblong; others tapering. Most of them have rather plump, 

 jointed, soft-skinned bodies, about half as broad as long, the widest part being 

 near the posterior extremity. The head and thorax are comparatively slim 

 and delicate. All the species have dark, compound eyes, a pair of long,, 

 jointed antenna coming out just in front of the eyes, a jointed sucking beak, 

 six jointed legs, and two nectaries which extend from the point of insertion on 

 the dorsal side of the abdomen as far back as the posterior extremity. These 

 nectaries seem to act as overflow valves for the excess of sap which the insect 

 imbibes when enjoying good forage. They give off this nectar when disturbed. 

 Ants are aware of this, and irritate the bee to get the nectar, which they 

 greatly relish. On this account, ants are almost invariably companions of the 

 plant lice of the field and garden. 



As has been suggested, aphides get their nourishment in the form of sap 

 from the parenchymatous, or soft tissue of the plant. This is done by means 

 of a beak or sucking tube (see fig. 1), with which all are provided. 



This is situated on the under side of the head, just in front of the anterior 

 pair of legs. Like the mouth-parts of other insects, this beak consists of a 

 number of divisions, such as the labrum, mandibles, maxillae, and labium. 

 The most prominent part is the labium. This consists of three joints, and is 

 a slitted tube — the slit being along its dorsal surface, or what would naturally 

 be called its anterior surface. To complete the tube and make it effective as- 

 a feeding organ, the mandibles and maxillae, as double organs, extend down, 



