INSECTA. 433 
Leaf-lice, Plant-lice, Pucerons. These animals live together on 
different plants and trees, and mostly in very large numbers. They 
do not leap, but run commonly very slowly. From the hind part 
of the body there often drops a transparent honey-sweet fluid, of 
which ants are very fond and on that account are often found 
in the neighbourhood of the leaf-lice. These suck the sap of the 
plants, and some species, by puncturing the leaves or leaf-stalks, 
produce excrescences or swellings occasionally hollow, which are 
filled with a great number of these animals and often with a 
considerable quantity of the sweet sap. The sticky fluid on leaves, 
known by the name of honey-dew, is caused by leaf-lice. Most 
species are covered with a powdery substance or with white threads, 
(a peculiar secretion of their body). 
To counteract the excessive multiplication of leaf-lice, in the great 
economy of nature, a number of enemies are on the watch, not 
merely ichnewmons (see above, p. 378), but insects especially which 
feed on them and devour large quantities, the pups of some diptera, 
of hemerobiit (p. 418), of beetles (Coccinelle), &e. 
LEEUWENHOECK had already noticed that plant-lice are viviparous, 
that they also lay eggs was first discovered by Lyoner; but the 
succession of generations, the descendants of mothers and grand- 
mothers which are viviparous and fruitful without copulation, was 
first discovered by Bonner ; see above, pp. 263, 264. 
Comp. on this group of insects, as numerous in species as interesting in 
their economy, Réaumur, Ins. 111. Mém. 1x. pp. 281—350; C. Bonner, 
Traité d’ Insectol. Tom. 1. Paris, 1745 ; Du Grrr, Mém. p. servir a U Hist. 
@Ins. WI. pp. 19—129, and for the systematic arrangement, Harrie, 
Versuch einer Eintheilung der Pfanzentaiise in GERMAR’S Zeitschr. f. die 
Entomol. 111. 1841, s. 359—376, and especially J. H. Kaurenpacu, Mono- 
graphie der Familien der Pflanzenlaiise. Mit Abbild. Aachen, 1843, Svo; 
also T, WALKER, Descriptions of Aphides, Ann. of Nat. Hist. sec. Ser. Iv. 
p- 202, Vv. 1850, pp. 14—28, 269—281, 388—395, VI. pp. 41—48, 
118—122. 
Some species live on the roots of plants. They have no wings ; BoucHs, 
however (according to RatzEBuRG, forst-Ins. 111. s. 216), discovered two 
species of Rhizobius that were winged. These species may be collected 
provisionally under the name of : 
Rhizopthiridium nob. 
Here belongs the genus 2hizobius Burm, (a name already given to a 
genus of Coleoptera), and the genera Paracletus, Trama and Forda V. 
HEYDEN, Lntomol. Beitrdége in Abhandl. der Senckenb. Gesellsch. 1. 1837, 
8. 291—295. hizoterus Hartic, according to KALTENBACH, does not 
differ from Forda V. HEypEn. 
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