80 



CEREAL AND FORAGE INSECTS. 



last instar because of the multitude of small, flattened, yellowish 

 tubercles with which the body is covered laterally, now darkens and 

 becomes a dingy green that renders it very inconspicuous among the 

 grass. Where low, bushy weeds abound, as in most of the range 

 country, the larvae seek shelter in them, preferring the smaller weeds 

 for this purpose. Where the weeds grow large, the central branches 

 are selected and the larvae concentrate there. 



The pupating caterpillar soon incloses itself within an open- 

 meshed network or reticulum of strong, very uneven silk fibers, and 

 this web is usually finished in twenty-four hours. This is the only 

 attempt at a cocoon made by very many of the larvae; but 50 per cent 



or more of the larvae inclose this coarse 

 web in a closely woven sack of much finer 

 silk, open at the top. (See fig. 44.) The 

 structure of the inner cocoon is so open 

 that the larva is able to protrude its head 

 and construct the finer one outside. 



Pupation takes place within a few days 

 or hours after the larva has inclosed 

 itself. Occasionally the larva lies dor- 

 mant for a week before transforming, but 

 usually the change takes place within a 

 day. The pupa gradually changes in 

 color from light brown to a very dark, 

 almost black hue, with dull purplish re- 

 flections in some cases. 



In localities where the larval food 

 supply is insufficient and the vitality of 

 the larvae is low, some of them live only 

 through the spinning process and die with- 

 out being able to pupate. The percent- 

 age that thus fails to pupate is difficult to 

 estimate, but is probably much less than 

 1 per cent. 



One curious fact that deserves mention here is the habit, very com- 

 mon where the caterpillars have been numerous, of two and even 

 three pupae occupying the same cocoon. Twin pupae are met with 

 everywhere, and often a single plant will contain several examples. 

 Where this doubling occurs there is no attempt at a partition in the 

 pupal chamber, nor is the space allowed for the twins or triplets 

 much, if any, greater than where a single pupa lies alone. It is some- 

 times possible at a glance to detect the presence of more than one 

 pupa by the greater density of the inclosing web, showing a com- 

 munity of effort. In rare instances two of the reticula are sur- 

 rounded by a common silk sac. 



Fig. 44.— The New Mexico range cater- 

 pillar: Single cocoon on Gutierrezia. 

 Reduced. (Original.) 



