August, ’23] 
HADLEY: JAPANESE BEETLE SPREAD 
351 
gives now a total of infested area, including portions of both Penn¬ 
sylvania and New Jersey, amounting to 7.73 square miles. 
Factors Primarily Responsible for Dispersion 
Natural Agencies of Dispersion. It is believed that the spread to 
date is probably largely due to natural agencies. This belief is based on the 
fact that the rate of spread, year b}^ year, has been fairly constant, in 
comparison with the increase in numbers of the insects for each year over 
the previous }^ear. The average yearly rate has been between 5 and 10 
miles outward. 
The flight of the beetle is probably the most outstanding natural 
agency of dispersion. The beetle is a strong and vigorous flyer, and is 
especially active during the hot summer days. Beetles will fly from 
tree to tree and probably from place to place for some distance in search 
of suitable food. Early in the beetle season suitable food is in abund¬ 
ance. As the season progresses, and the defoliation of suitable food 
plants becomes more complete, there is apparently a tendency for the 
insects to range further in search of food. While it is not possible to 
say definitely the greatest distance which an individual beetle can fly, 
experiments have been conducted in connection with this point, during 
the course of which marked beetles have been recovered at least a mile 
and a quarter away from the point of releasement. It is not supposed 
that this distance was covered in one single flight, but more probably in 
a series of flights. Flight also occurs in the search for a suitable place 
for deposition of eggs by the female, and it has been noted also that 
males will accompany females to a certain extent on these occasions. 
Probably, however, the distance travelled on such occasions is less than 
when the insects are in search of food. 
Dispersion of the insects by winds and storms is probably not an 
important factor. While it may be true that a few beetles may be 
carried some distance by strong winds, it has also been noted that 
normally beetles will fly against rather than with the wind. This fact 
would tend to limit the distance of flight rather than to increase it. 
It is possible that waterways are factors of some importance in the 
dispersion of the beetle. For example, individual beetles have been 
picked out of the water of the Delaware River where it flows through the 
infested territory, at a distance of several hundred yards from the in¬ 
fested shore line. Experiments have shown that the beetles are quite 
well able to float in water with the current, unless seized by fish or birds. 
It is quite possible that some beetles may have been carried some dis- 
