FEEDING HABITS OF THE JAPANESE BEETLE. 5 
Table \ -Sex of the first 10 Japanese beetles (Popilliajaponica) to infest food plants 
between 7.45 and 9 a.m., July 10 to 20, 1921, Riverton, N. J. 
Food plants. 
Peach 
Do 
Do 
Do 
Do 
Sour cherry . 
Do 
Do 
Do 
Do 
Corn . . . 
Do. 
Do. 
Do. 
Do. 
Grape. . 
Do! 
Apple. . 
Total females.... 
Per cent females. 
Sex of first 10 beetles to arrive. 
2 3 
5 6 7 8 9 10 
Number 
of 
females. 
3 8 5 6 10 6 4 8 11 6 67 
15 40 25 30 50 30 20 40 5o 30 33. o 
There were only three females among the first beetles to arrive 
on the 20 different plants under observation. Of the second beetles 
to arrive on the plants, 8, or 40 per cent, were females Of the third 
beetles, 25 per cent were females. The proportion of females among 
the 4, 5, 6,7, 8, 9, and 10 beetles was 30, 50, 30, 20, 40, 55 and 
30 per cent, respectively. There were not less than 2 or more than 
5 females among the first 10 to arrive on any one plant. Data 
reported under the next heading indicate that the percentage of 
female beetles on similar plants during the hours when these observa- 
tions were made is between 20 and 30 per cent. . Therefore, the 
chances are about 1 to 4 or 5 that, on a numerical basis female beetles 
will be the first to infest or reinfest a food plant. On the basis of 
the data collected, one sex is as likely as the other to begin a new 
infestation, providing there are equal numbers of both sexes Hying 
at the time. 
PROPORTION OF SEXES ON VARIOUS TYPES OF FOOD PLANTS. 
Collections of beetles were made in July and August at hourly 
intervals during the day from several different food plants. Apple 
trees were selected as representing the taller type of plants; corn 
grapes, and althea or rose of Sharon (Hibiscus syrmcus), those of 
medium height; and smartweed, evening primrose, mercury weed, 
and the velvet-leaved mallow, those with low-growing habits. A col- 
lection of between 100 and 125 beetles was made at random iromtne 
plants at each hour. The collections were kept in separate bottles 
and were later sorted and the sex determined Figures 1,2, and 3 
illustrate graphically the percentages of female beetles obtained m 
these collections. . , ... , 
In Figure 1 are shown the percentages of female beetles in two 
series of hourly collections between 7 a. m. and 8 p. m. from smart- 
32095—23 2 
