MANAGING ADULT JAPANESE BEETLES

By L. H. Townsend, Extension Entomologist

University of Kentucky Department of Entomology

The Japanese beetle is a devastating pest of urban landscape plants. It was first found in Kentucky on the southern outskirts of Louisville (Jefferson County) in 1937. The isolated infestations were treated with insecticides and eliminated, delaying the spread of the beetle. However, populations in the region increased dramatically during the 1950s and '60s; the Japanese beetle now occurs in all 120 counties in the Commonwealth.

Description and Habits

R. Bessin, Univ. of Kentucky

Adult Japanese beetles are 3/8 inch long metallic green beetles with hard, copper-brown wing covers. Five small white tufts project from under the wing covers on each side, and a sixth pair at the tip of the abdomen. These white tufts help to distinguish them from similar metallic green or coppery colored beetles.

Adults emerge from the ground in late May or early June. Individual beetles live about 30 to 45 days with activity concentrated over a four to six week period. Beetle numbers begin to decline in late July but some can be found as late as September.

Japanese beetles can feed on about 300 species of plants, ranging from roses to poison ivy. Odor and location in direct sun seem to be very important factors in plant selection. The beetles usually feed in groups, starting at the top of a plant and working downward. While a single beetle doesn't eat much; group feeding by many causes severe damage. Adults feed on the upper surface of foliage, chewing out tissue between the veins. This gives the leaf a characteristic skeletonized appearance.

Japanese beetles can fly as far as 5 miles but 1 to 2 miles is more likely. Usually, they make only short flights as they move about to feed. Local infestations spread as beetles move to favored food and egg-laying sites.

Insecticides for Japanese Beetle Control

Many insecticides are labeled for Japanese beetle control on landscape plants. Examples include acephate (Orthene Turf, Tree & Ornamental Insecticide), carbaryl (Sevin and many other brand names), cyfluthrin (Bayer Advanced Garden Multi-Insect Killer Concentrate), lambda-cyhalothrin (SpectracideŽ TriazicideŽ Soil & Turf Insect Killer Concentrate), esfenvalerate (Ortho Bug-B-Gon Garden & Landscape Insect Killer Concentrate), and permethrin (SpectracideŽ Bug Stop Multi-Purpose Insect Control Concentrate and many other brands). Neem extracts (Bon-Neem) deter Japanese beetle feeding but may not be adequate against high populations.

Direct spray applications of insecticidal soap kills Japanese beetles on contact but does not provide any residual protection.

Here are some points to keep in mind when using insecticides for beetle control -

• Japanese beetle flight is greatest on clear days with temperatures between 84o and 95o F and winds less than 12 miles per hour. This can bring new beetles into your landscape to challenge any control program that you may have. When these conditions exist, check plants frequently to see if beetles are starting to feed again.

• A few beetles on plants, or some moderate damage, will bring in more. Japanese beetles apparently produce aggregation pheromones that will attract more males and females to feed and find potential mates. In addition, volatile odors from damaged plants may attract more beetles. These conditions also can keep beetle numbers high. Keeping numbers and damage low can mean fewer new arrivals.

• Japanese beetles begin to feed at the tops of plants and move down as defoliation occurs. This makes damage obvious, in terms of brown leaves and esthetic damage, but also can pose coverage problems on large trees. Hose end sprayers may allow applications to reach the target but spray drift and applicator exposure are potential problems.

• Some of the effective insecticides for Japanese beetle control, such as carbaryl (Sevin) and the pyrethroids (permethrin and others) can contribute to build-ups of mites or aphids. Watch closely for signs of these pests and use acephate or malathion if needed. While these insecticides have a shorter residual life, they may help to reduce problems with secondary pests.

Repeated applications may be necessary because of the relatively short residual effect of the products. Also, a significant rainfall shortly after an application may reduce the insecticide deposit below effective levels.

Natural Controls

The hard body of the Japanese beetle may make them relatively unattractive to many predators, such as birds. Some may be killed by predatory insects but this is probably infrequent. A few species of wasps and flies have been imported an attempt to control the beetle in the US but with only establishment has been limited, so far.

Collecting Beetles

Hand collecting can be used to protect valuable plants when beetle activity is relatively low. The presence of beetles on a plant attracts more beetles. When you remove beetles daily by hand from a plant, only about half as many are attracted to that plant compared to those on which beetles are allowed to accumulate. One of the easiest ways to remove beetles from small plants is to shake the plants early in the morning (about 7 a.m.) when temperatures are low and the beetles sluggish. The beetles may be killed by shaking them into a bucket of soapy water.

Trapping Beetles

Japanese beetle traps are sold in many garden centers. Commercially available traps attract the beetles with two types of baits. One mimics the scent of virgin female beetles and is highly attractive to males. The other bait is a sweet-smelling food-type lure that attracts both sexes. This combination of ingredients is such a powerful attractant that traps can draw in thousands of beetles in a day.

Research conducted at the University of Kentucky has shown that the traps attract many more beetles than are actually caught. Consequently, susceptible plants along the flight path of the beetles and in the vicinity of traps are likely to suffer much more damage than if no traps are used at all. In most landscape situations, use of Japanese beetle traps probably will do more harm than good. If you experiment with traps, be sure to place them well away from gardens and landscape plants.

Plant Selection

Careful selection of plant species when replacing or adding to your landscape is the key to avoiding an annual battle with Japanese beetles. Certain common landscape plants are inevitably attacked and may be poor choices where this insect is abundant (Table 1).

Plants which grow rapidly and are especially attractive to the beetles are most difficult to protect. Roses unfold quickly and are especially attractive to beetles. When beetles are abundant, nip buds and spray to protect the leaves or cover the roses with netting to keep beetles out.

Beetles are fond of certain weeds and non economic plants such as bracken, elder, multiflora rose, Indian mallow, sassafras, poison ivy, smartweed, wild fox grape and wild summer grape. Elimination of these plants whenever practical destroys these continuous sources of infestation.

Many common trees and shrubs are relatively less attractive to the beetles and using them can reduce the annual frustrations of the beetle season (Table 2).

CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.

Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!