350 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 16 
to cover an area approximately 2.7 square miles in extent, of which 
about .5 square mile was heavily'infested. 
In 1918 more intensive scouting was carried out and the infestation 
was found to have increased to such an extent as to cover an area of 
approximately 6.7 square miles, as measured on the map. Up to this 
year the numbers of the insect were still comparatively small, and the 
spread not to be considered especially extensive in comparison with the 
spread of later years. 
In 1919 the numbers of the insects in the heavily infested area had in¬ 
creased to a point where in the centre of the infested territory, beetles 
could be found in what may be considered decided abundance. During 
the summer of 1919, the spread was considerable, and a total of 48.3 
square miles was found to be infested. Up to and including this season, 
no Japanese beetles had been found across the river in Pennsylvania, the 
entire infestation still being confined to New Jersey. 
In 1920 there was again a large increase in infested territory, and for 
the first time beetles were found across the river in Pennsylvania. It 
is probable, however, in view of the numbers found there during this 
season, that the insect had actually reached the Pennsylvania side of the 
Delaware river during the preceding season, (1919) but in numbers so 
small as not to have been observed in the scouting of that season. At 
the end of 1920, the infested area in New Jersey was 92 square miles, and 
in Pennsylvania 11 square miles, making a total infested area of 103 
square miles. 
In 1921 the greatest outward spread up to that time occurred. During 
the summer of 1920, and to a less extent during the preceding summers, 
strenuous efforts had been made to prevent the spread of the insect, 
by a program of dusting and spraying around the infested area. How¬ 
ever, the spread which occurred, especially during the seasons of 1919 
and 1920, had seemed to show that repressive measures as followed were 
not sufficiently effective to justify their continuation. During the 
summer of 1921 the beetles had increased in numbers to a very marked 
extent, and there was an increase in infested area probably in direct 
proportion to the increase in density. At the end of this season, the 
infested area in New Jersey amounted to 213.5 square miles, and in 
Pennsylvania 56.5 square miles, a total of 270 square miles all told. 
During the season just passed, that of 1922, there again has been an 
increase both in density and area of infestation, more or less in direct 
proportion. The spread has been fairly general in all directions, and 
