of Rhode Island GreenShare Factsheets
Japanese beetles are one of the most
common pests in Northeast gardens. They were accidentally
introduced with infested irises
from Japan for the 1916 World's Fair. The adults feed on over
300 different plants, "skeletonizing" the leaves and leaving
only midribs and other veins. When populations are high, they
may defoliate plants. The larvae (grubs) feed on roots and
can kill large areas of turf (see white
Adults are approximately 10 mm (3/8 inch) long, with a
metallic green midsection and head. The wing covers are coppery
brown, and tufts of white hairs line the sides of the abdomen.
The life cycle is completed in one year, with ten months
spent as a grub in the soil and two months as an adult. Females
deposit eggs in soil, usually in turf, during the summer (primarily
in July). Grubs feed on roots near the soil surfaces until cold
weather arrives, then move to about 15 cm (6 inches) below the
surface of the soil to they hibernate for the winter. Grubs move
nearer the surface in the spring and resume feeding. They pupate
in May and June, emerging in early July as adults.
Roses, fruit trees, beans, tomatoes, and corn are among
the favorite foods of the adult Japanese beetle. Adults feed
during the day, especially in warm weather and on plants in full
sun. They chew on the flowers and the leaves, which soon wilt
and drop. Large populations can completely defoliate a plant.
There are several similar species, such as Oriental and Asiatic
garden beetles, which also eat landscape plants. Oriental and
Asiatic garden beetles feed mostly during the night on flowers,
but cause little damage as adults (the larvae can seriously damage
roots, particularly of grasses).
Light infestations can be controlled by knocking the adults
into a pail of soapy water early in the morning, while they are
still sluggish. The plants can also be sprayed with Neem, which
is approved for organic gardens and acts as a feeding repellant.
Commercially available Japanese beetle traps use two chemical
lures to attract the beetles: one lure is a Japanese beetle sex
pheromone that attracts male beetles; the other lure consists
of a blend of three chemicals which emulates a floral scent and
attracts males and females. One study has shown that using these
traps in an individual yard may not be effective. Traps will
exert some degree of control, but the number of traps to use,
and how effective they are, remains a topic of debate among entomologists.
Using these traps in a small residential yard may be counter-productive,
as they may attract more beetles into the yard than they kill.
Traps may be effective, however, in a home yard surrounded by
forest, on a golf course or in a residential community where
all neighbors simultaneously trap Japanese beetles, or in other
sites where the traps do have the potential to suppress the local
By Marion Gold, Steven
Alm and Meggan Gould, 1999
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program