100 BULLETIN 1476, U. S. DEPARTMENT OF AGRICULTURE 
The actual distance traversed by migrating larvae in the field has 
not been determined with accuracy, although infested cornstalks 
have been found at a distance of about 15 feet from the location 
of the nearest known original egg cluster in a very lightly infested 
corn plat. In a series of controlled experiments wherein crawling 
larvae of each instar except the second were restricted to sheets of 
paper from 5 to 6 feet in length, without food, until death resulted, 
the average distance covered by larvae in the first instar was 31 feet 
3 inches ; third instar, 118 feet 1 inch ; fourth instar, 79 feet 8 inches ; 
fifth instar, 170 feet ; and sixth instar, 97 feet 1 inch. These experi- 
ments, of course, do not give reliable information relative to the 
probable migrating ability of the larvae in the field and are only 
indicative as showing their power of locomotion. 
HIBERNATION 
The European corn borer normally passes the winter as a full- 
grown larva within the tunnel made in its host plant during the 
previous summer and fall. If, however, the host-plant material is 
unduly disturbed during the progress of field work, or if for any 
other reason the plants containing the larvae do not afford suitable 
quarters for winter shelter, many of the larvae migrate from their 
hosts and enter other plants. Under conditions of severe infestation 
the larvae have entered such woody stemmed plants as blackberry, 
raspberry, sumac, elderberry, and grape. If suitable plants are 
not available for winter shelter, the larvae often burrow into such 
objects as the walls and crevices of buildings, fences, and posts. 
Here they form short tunnels in which to pass the winter. When 
more suitable winter quarters are lacking, the larvae sometimes secrete 
themselves in loose leaves, under the loose bark of trees or fence 
posts, and underneath rubbish, clods of soil, loose stones, and similar 
objects. Here they may. or may not, inclose themselves entirely 
or partially with a rough silken web. Many of these larvae which 
seek shelter in locations other than plants, as mentioned above, have 
been found by experimentation to pass the winter successfully and 
subsequently to pupate and emerge as moths; providing that the 
moisture conditions of their habitat were suitable for normal hiber- 
nation and pupation. 
In every instance under observation all of the hibernating larvae 
were in the last instar. No case of molting in the spring has been 
observed. 
LARVAL MORTALITY DURING HIBERNATION 
Dissection of Pi/rausta niibUalis larvae during their period of 
hibernation has revealed that the vital organs are surrounded with 
a layer of tissue resembling fat. Apparently this fatty material 
greatly aids the hibernating larvae not only in surviving the adverse 
natural conditions to which they are exposed during this period but 
also supplies available means for carrying on the metabolism which 
occurs during this long period of comparative inactivity. It may 
also aid the hibernating larvae in resisting such artificial influences 
as fumigation and heat, 
The normal percentage of winter mortality in plants left in natu- 
ral position in the field is comparatively low. Table 31 gives data 
relative to the winter mortality for a five-year period in represen- 
