10 BULLETIN 1154, U. S. DEPARTMENT OF AGRICULTURE. 
time. This, together with the fact that the species is undergoing a 
period of seasonal change and readjustment brought about by its 
new environmental conditions and its increasing numerical concen- 
tration, renders the problem of its control by sprays one of consider- 
able difficulty. This applies not only to the chemical aspect of the 
insecticidal investigations necessary for a successful culmination of 
the work but also to the biological phases of the problem as well. 
SUMMARY. 
The control of the Japanese beetle has been handicapped by the 
fact that when the arsenic als used in commercial practice have been 
applied to the food plants of this insect only a small number of the 
beetles have been killed. Usually the infestation of the beetles on 
the sprayed plants is greatly reduced and reinf estation may be entirely 
prevented. This condition, together with the gregarious habits of 
the beetles, tends to concentrate the insects on plants which for 
economic reasons it is difficult to protect by sprays. 
This insect has been recorded as attacking 210 species of plants. 
The most severe injury is confined to between 20 and 25 species, 
including most of the cultivated fruit trees, corn, and beans, besides 
various shade trees and ornamental shrubs. 
The degree of infestation on the food plants is variable. Instances 
were noted on peach, smartweed. sassafras, and apple where the 
plants were heavily infested for a while, after which the beetles 
left for other food plants; in some cases the plants were not again 
infested during the season. 
Ripening fruit of an} T kind, silk and ears of corn, and peaches 
affected with brown rot are particularly attractive to the beetles. 
So numerous do the insects become at times that prematurely 
ripened peaches and apples are completely covered with a swarming 
mass of beetles. 
During the early part of the season the beetles are more abundant 
on weeds, cherries, and grapes; by midsummer, fruit and shade trees 
are more heavily infested, while during August and September 
heavy infestations are mostly confined to corn, beans, clover, and 
various plants in bloom at that time. 
Most of the feeding occurs on the upper and outer foliage of the 
various food plants, especially where they are exposed to the direct 
rays of the sun. 
Other workers have found that the greatest activity among the 
beetles occurred at 38° to 39° C. The observations of the writer 
showed that there is a general increase in the activity of the beetles 
until 2 or 3 p. m., after which time their activity decreases until 
dark, when flight ceases. 
In a majority of cases the females enter the soil late in the after- 
noon, deposit from 1 to 4 or 5 eggs, and emerge the following morn- 
ing to feed and mate. Some females may remain three or four 
days in the soil before they emerge again to feed. In many cases, 
however, eggs are laid, only every third or fourth night. 
There is a distinct movement of the male beetles to those plants 
on which females are feeding, and during the early part of the day 
the beetles tend to concentrate on low-growing plants such as smart- 
weed and beans. 
