If the oviparous generation be added to this you will have a thirty times greater result" The female Aphides thus produced must be regarded as larvae, but they present a more developed condition than the larvto of Coleoptera and Lepidoptera. The compound eyes are developed on the head, and the antemue have acquired their mature form and proportions ; the six thoracic legs have attained their due growth and development.
The only change which these fertile larvae afterwards undergo is increase of size, and development of the reproductive tissues. In the last generation, which, according to the species of Aphis, is the seventh, ninth, or eleventh, the power which they possess of producing iielividuals like themselves ceases. In the last generation wings are actkuired, and male bisects also with wir,e, appear. It is these insects which produce eggs, and deposit them where, under the genial influences of the sun, they are hatched, and thus produce the multitudes which make the attacks of these creatures so remarkable.
The number of species of Aphis is very large. In the List of Specimens of Homopterous Insects' in the collection of the British Museum, drawn tip by Mr. Francis Walker, 326 species of this genus are described. Almost every species of plant gives snpport to a different species of Aphis, each of which has been described with very great accuracy in the list above mentionteL The effects of the attacks of these insects is sometimes of national importance. In the year 1802 the hop-duty fell from 100,0001. to
14,0001., on account of the great increase of the Aphis. When the Aphis has been absent the duty has risen as high as 500,0001. The ApAia Roam is most destructive to the beautiful plant on which it is constantly found. Apple-trees and pear-trees are attacked with a species which injures greatly their produce. In most cases these insects are green, but a black species attacks the bean ; whole acres of these plants will be suddenly covered by these insects. Their attacks on all plants seem regulated by the health of the plant If atmospheric conditions occur which render plants unhealthy, then the Aphis makes its appearance. If these cease, the Aphis then disappears also, and one crop of plants will be attacked several times in the same year. The Aphidtes have their natural enemies. The lame of the Lady-Birt1 (Coccinclla), the Syrphua or Bee-like Fly,the Ileincrobiza perle, and several species of Ichneumonithe, devour with great avidity several species of Aphis.
The chief remedy for the deatniction of the Aphis is tobacco. Where plants can be brought together under cover they may be easily exposed to tobacco fumes, but in the open air this is not so easily effected. In this case the best plan is to apply the tobacco in water. The affected branches or parts of plants may be syringed with the infusion, and afterwards washed with pure water.