BLUE-GREEN CATERPILLARS 397 



larvae of this parasite rapidly develop within the tissues of 

 the caterpillar and come to the surface of the skin, where each 

 immediately spins a silken cocoon, normally of golden yellow. 

 To my great surprise the braconid cocoons upon the surface of 

 the parasitized blue-green caterpillars were not bright yellow, 

 but pure white. After feedmg upon the blue-green, yellow-free 

 blood of the host, the secretion of their silk glands had become 

 pure white. 



Unlike white cocoon color in Plusia moneta (Bird, '03 ; Hawkes, 

 '16) and Clisiocampa neustria (Hawkes, '16) that turns yellow 

 in a moist atmosphere, white in the cocoons of Apanteles emerging 

 from a blue caterpillar remains unchanged in the presence of 

 moisture. 



CONCLUSION 



It is exceedingly probable that normal yellow silk of Apanteles 

 flaviconchae, parasitic upon normal yellow-green caterpillars, 

 gets its color from a xanthophylloid element in the hemolymph, 

 derived from the food plant. This the blood of the blue-green 

 caterpillar lacks. Consequently, the parasite of the blue-green 

 caterpillar spins white, instead of yellow, silk. 



DISCUSSION 



There is in this case no opportunity to appeal to chromosomes 

 of the spinning glands of the braconid larvae for an explanation 

 of the yellowness of their product. The yellowness is due directly 

 and absolutely, so far as my observations go, to the blood of the 

 host and not to hereditary enzymes in the chromosome of the 

 spinning glands. 



That being so, we must infer that a similar explanation holds 

 for the grass-green of the hypodermis, yellow color of the pupal 

 cuticula, and for adult eye color, of the host, Colias philodice, 

 for they show a similar relation to blood pigments in that if 

 yellow is suppressed in the blood it will be lacking in the very 

 permeable hypodermal cells and their secretions; that is, in the 

 cuticula of the pupa and in the compound eye. Here, too, we 

 may disregard the possible local action of the chromosomes 



