ENTOMOLOGY 



weed (Asclepias). In many instances .an insect feeds indifferently upon 

 several species of plants provided these have certain attributes in com- 

 mon. Thus Argynnis cybele, aphrodite and atlantis eat the leaves of 

 various species of violets, and the Colorado potato beetle eats different 

 species of Solanum, Papilio thoas feeds upon orange, prickly ash and 

 other Rutaceae. Anosia plexippus eats the various species of Asclepias 

 and also Apocynum andros<zmifolium; while Chrysochus also is limited 

 to these two genera of plants, as was said. These plants agree in having 

 a milky juice ; in fact the two genera are rather nearly related botanically . 

 The common cabbage butterfly (Pieris rapce) though confined for the 

 most part to Cruciferae, such as cabbage, mustard, turnip, radish, horse- 

 radish, etc., often develops upon Tro- 

 pcBolum, which belongs to Geraniaceae; 

 all its food plants, however, have a 

 pungent odor, which is probably the 

 stimulus to oviposition. 



Most phytophagous insects, how- 

 ever, range over many food plants. 

 The cecropia caterpillar has more than 

 sixty of these, representing thirty-one 

 genera and eighteen orders of plants; 

 and the tarnished plant bug (Lygus 

 pratensis) feeds indifferently on all sorts 

 of herbage, as does also the caterpillar 

 of Diacrisia mrginica. Many of the 

 insects of apple, pear, quince, plum, 

 peach, and other plants of the family 

 Rosaceae occur also on wild plants of 

 the same family; and the worst of our corn and wheat insects have 

 come from wild grasses. As regards number of food plants, the gypsy 

 moth " holds the record," for its caterpillar will eat almost any plant. 

 In Massachusetts, according to Forbush and Fernald, it fed in the field 

 upon 78 species of plants, in captivity upon 458 species (30 under stress 

 of hunger, the rest freely), and refused only 19 species, most of which 

 (such as larkspur and red pepper) had poisonous or pungent juices, or 

 were otherwise unsuitable as food. The migratory locust is notoriously 

 omnivorous, and perhaps eats even more kinds of plants than the gypsy 

 moth. 



Galls. Most of the conspicuous plant outgrowths known as " galls" 

 are made by insects, though many of the smaller plant galls are made 



FIG. 248. Holcaspis globidus. A, 

 galls on oak, natural size; B, the gall- 

 maker, twice natural length. 



