S. DEPARTMENT OF AGRICULTURE. 
the beetles and greatly reduces or on occasion entirely prevents sub- 
sequent reinfestation. If adjacent unprotected crops are in a suitable 
condition for the beetles to feed upon, it is reasonable to suppose that 
the infestation of these would be somewhat increased owing to the 
fact that a portion of the normal feeding area of the beetles was ren- 
dered distasteful by the spray. The increase in degree of infestation 
might or might not be in proportion to the reduction in infestation on 
the sprayed foliage. The writer and other workers have noted that 
under conditions favorable for activity among the beetles the degree 
of infestation increases in a somewhat direct proportion to the number 
of beetles on the plant. In other words, there is a gregarious instinct 
which attracts the insects to plants on which other individuals of the 
same species are feeding. Since this beetle has a wide range of food 
plants, is an active and strong flier, and is decidedly gregarious, the 
need for detailed studies of its biological relationships is apparent. 
FEEDING HABITS OF THE JAPANESE BEETLE. 
Regarding its food habits, the Japanese beetle may properly be 
termed polyphagous, having been recorded as attacking 210 species 
of plants, which are distributed among 59 families. In the past 
certain species more than others have been injured by the beetles. 
Among the cultivated crops may be mentioned apple (Pyrus mains), 
peach (Amygdalus persica), grape (Vitis spp.), cherry (Primus spp.), 
corn (Zea mays), and string bean (Phaseolus vulgaris). Shade trees, 
such as elm ( Ulmus spp.), oak {Quercus spp.), and willow (Salix spp.), 
are usually preferred food plants, while smartweed (Polygonum spp.), 
evening primrose (Oenothera biennis), sassafras (Sassafras sassafras), 
and elder (Sambucus canadensis) represent the herbaceous plants 
and shrubs. The beetles do not feed consistently on plants of any 
one type, hence a general statement that one particular species is 
preferred can not be made. Almost no plants, excepting certain 
conifers, are exempt from attack between June and November when 
the beetles are present. At times they will be found abundantly on 
low-growing plants such as alsike clover (Trifolium Jiybridum), white 
clover (T. repens), violet (Viola spp.), or galinsoga (Galinsoga spp.), 
or they may feed on the taller shade trees. It was first believed that 
the succulency of the leaves influenced the insects to a great extent 
in the selection of their food plants. Later observations indicate 
that this in itself is not the determining factor in the apparent prefer- 
ence shown for certain species. During the period between June 18 
and June 30, 1921, a 2-year-old peach orchard became infested and 
the foliage on the mature wood was eaten first; in all about 30 per 
cent of the leaves were injured by the feeding of the insects. Between 
the 8th and the 12th of July, when the abundance of the beetles was 
at its height, they left these peach trees for other food plants. These 
particular peach trees were not reinfested during the season, although 
a sour cherry orchard adj acent to the peaches was more or less heavily 
infested from June to October. Similar facts were noted in a bearing 
peach orchard about 100 yards from the young orchard mentioned, 
except that the beetles did not leave until August. 
A large patch of smartweed, near the center of the area in which 
this insect is most abundant, became infested June 17, 1921. By 
July 1 hundreds of beetles were present on the plants each day. On 
