86 NINETEENTH REPORT STATE ENTOMOLOGIST OF MINNESOTA—IQ22 
The hypodermal colors are subject to change during the active 
life of the insect. But the change of color in adult bugs is always 1n 
one direction, from white to red, or from yellow to red. Once the 
yellow or red color has been attained in the hypodermis of thé adult, 
it remains throughout the life of the bug. Large numbers of adult 
bugs have been kept under observation, at both high and low tem- 
peratures, but in no case has the red color been reduced. The case 1s 
different with growing nymphs. During the last three nymphal instars 
the yellow color may change to red, or under other conditions, notably 
high temperatures, the red of a fourth stage nymph may change to 
yellow, and from that to white in the fifth instar. Thus the color 
pattern of an adult is determined largely by conditions under which 
the nymph has developed; for once having attained the adult stage, 
the cuticular, or black color pattern, can not be changed, while the 
hypodermal colors can change only in one direction, white to red, or 
yellow to red as the case may be. 
Change of Color in Adult 
As brought out above, the change in hypodermal colors of the 
adult Perillus 1s always in one direction, from white to red, or from 
yellow to red. The change of color in the typical white color form 
is of particular interest. In this form a yellow stage can scarcely 
be detected, for the appearance of color in the white pattern is almost 
immediately that of red. It is also noticed that the red color appears 
first at basal angles of pronotum, tip of scutellum, apex of corium, 
and ventral areas of the abdomen. From these points it progresses 
outward until in the final stages all the white areas may appear deep 
red. Male specimens turn red much more rapidly than do females, 
and in fact it is difficult to keep white males as long as two weeks 
without the red color developing. An examination of the hypodermis 
at points where the red color is just appearing, shows that the granules 
in the hypodermal cells are yellow at first but change very soon to 
red, or at least by the time the cell is well filled with granules. It 
appears that once these pigment granules have formed in the adult 
hypodermis, reduction never takes place. 
The typical yellow color form has the hypodermal cells filled with 
yellow granules. Under certain conditions, notably temperatures of 
78°F, or above, this color may be maintained unchanged. When the 
temperature goes below 75°F. for a few days, the yellow color begins 
to take on an orange-red cast, and if the bug lives six or seven weeks 
it may become deep red in color. During hibernation there appears 
