No. (533] FOOD-PLANTS AND INSECTS 



327 



togeny, the statement has boon made that some Lepidop- 

 terous caterpillars occur on a greater range of plants 

 when young, or at least that they will readily feed upon 

 certain kinds during the earlier instars, and refuse them 

 later, so that their diet becomes more restricted as 

 growth progresses. This statement has been in turn used 

 as an argument that oligophagous forms are .derived 

 from more restricted feeders, and that they repeat in a 

 way their history by the limitation of their food-plants 

 during successive instars. 



Some elaborate experiments on the feeding habits of 

 the gipsy-moth reported on by Mosher tend to discredit 

 this supposition, however. As is well known, the gipsy- 

 moth occurs on a wide range of plants, but shows well- 

 marked preferences for certain among them which repre- 

 sent its favored food. These experiments were carried 

 out in the extensive detail possible only when dealing 

 with insects of great economic importance, and although 

 planned for another purpose, furnish valuable data upon 

 this point. It appears that on a number of their numer- 

 ous food-plants, the gipsy-moth caterpillars show an in- 

 ability or at least an unwillingness to feed either during 

 the very early or during the later larval stages. On 

 some kinds of trees the early larvae failed to develop and 

 on others the latter stages did not feed, although the 

 young ones did so. This diversity of behavior is in part 

 due to the fact that young larvae cannot usually feed upon 

 conifers, while the older ones eat the foliage of these trees 



