PROGRESS REPORT OX THE EUROPE AX CORX BORER 129 
water dispersion may not be an annual occurrence, but may vary 
considerably from year to year, depending on a number of natural 
factors. 
THE WATER CURRENTS OF LAKE ONTARIO 
The water currents of Lake Ontario (fig. 51) are suggestive of the 
possible means of spread of the insect to the territory about this lake 
now known to be infested. Here the infestation on both the north- 
ern and southern shores has been found to be spreading more rapidly 
along the shores of the lake. The water currents indicate that if 
water drift of infested cornstalks does play an important part in the 
dispersion of the insect, their direction is such as to carry infested 
cornstalks to all the shores of the lake, as well as to carry them into 
the St. Lawrence River, thus opening up a large area to possible 
infestation by this insect. 
Dispersion in Relation to the Season 
The period of maximum flight of adults in the area about Lake 
Erie extends over a period of two or three weeks in July and early 
August, so that dispersion by flight must take place within this short 
period. Larvae becoming full grown by late August or September 
remain in the host plant until the following June, and during most 
of this time they are inactive. Over all this period, therefore, dis- 
persion by the movement of infested stalks may take place, and from 
November to April the disposition of the stalks would be attended 
by little movement of larvae since they are in a dormant condition. 
The Natural Phenomena of Spring 
The melting of snow in the spring and the breaking up of ice 
usually result in a swelling of streams and rivers, an increase in 
the rapidity of flow in many of them, and the distribution of debris 
that has been brought to them by the melting snow and ice. There 
are, then, two ways in which infested cornstalks may be distributed 
by water: (1) By floating free cornstalks, which .may take place at 
any time during the fall, winter, or spring, and (2) by the distri- 
bution of cornstalks frozen in blocks of ice, which takes place mainly 
during the general thaws in the spring. In connection with this 
point, a note by Crawford (1) may be highly suggestive. He states 
that on April 4, 1923, " Considerable quantities of cornstalks were 
found to have been carried into Lake Erie by water from the spring 
floods. Material was also found frozen in the dislodged ice. This 
ice was later blown out into the the lake by the winds from the 
north, suggesting a probable means of infesting- the southern shore 
of Lake Erie." The same authority has reported the finding of a 
submerged infested cornstalk at a point in Lake Erie 17 miles from 
Port Stanley, Ontario. In this case, although there was considerable 
scouting on the southern shore of Lake Erie in the spring of 1923, 
no cornstalks were found to have been cast on shore, so that it 
appeared that this material had not reached the southern shore of the 
lake that year. 
In many cases it is probable that the insects may be more suc- 
cessfully transported by cornstalks frozen in ice than in free stalks, 
25411°— 27 9 
