–by Dr. Raymond Cloyd
Japanese beetle, Popilla japonica, adults are present throughout most of Kansas feeding on many plants including: roses, Rosa spp.; littleleaf linden, Tilia cordata; Virginia creeper, Parthenocissus quinquefolia, and grape, Vitis vinifera. The ways to manage populations of Japanese beetle adults are limited, and have been for many years, with the application of insecticides still being the primary strategy. Japanese beetle adults are one of the most destructive insect pests of horticultural plants in landscapes and gardens. In addition, the larva or grub is a turfgrass insect pest in home lawns, commercial settings, and golf courses.
Japanese beetle adults are 3/8 to 1/2 inch long, metallic green with coppery-brown wing covers, and approximately 14 tufts of white hair along the edge of the abdomen (Figure 1).
Fig 1. Japanese Beetle Adults Feeding On Leaf (Auth–Raymond Cloyd, KSU)
Japanese beetle adults emerge from the soil and live up to 45 days feeding on plants over a four-to-six-week period. Adults feed on many horticultural plants including: trees, shrubs, vines, herbaceous annual and perennials, vegetables, fruits, and grapes (Figures 2 and 3).
Fig 2. Japanese Beetle Adults Feeding On Grape Leaf (Auth–Raymond Cloyd, KSU)
Fig 3. Japanese Beetle Adults Feeding On Grape Leaf (Auth–Raymond Cloyd, KSU)
Plant placement in the landscape and the volatiles emitted by plants are factors that affect adult acceptance for
feeding. Furthermore, Japanese beetle adults produce aggregation pheromones that attract males and females to the same feeding location. Adults can fly up to five miles to locate a host plant; however, they tend to only fly short distances to feed and for females to lay eggs.
Japanese beetle adults feed through the upper leaf surface (epidermis) and leaf center (mesophyll), leaving the lower epidermis intact. Adults, in general, do not feed on tissue between leaf veins, resulting in leaves appearing lace-like or skeletonized (Figure 4).
Fig 4. Japanese Beetle Adult Feeding Damage On Leaf (Auth–Raymond Cloyd, KSU)
Adults are most active during warm days, feeding on plants exposed to full sun throughout the day, which may be why roses are a susceptible host plant since roses require at least six hours of direct sunlight to flower. Japanese beetle adults start feeding at the top of plants, migrating downward after depleting food sources. Japanese beetle adults will also feed on flowers (Figure 5), chewing holes in flower buds, which prevents flowers from opening or causes petals to fall prematurely.
Fig 5. Japanese Beetle Adults Feeding On Rose Flower (Auth–Raymond Cloyd, KSU)
Managing Japanese beetle adult populations involves implementing a variety of plant protection strategies, including: cultural, physical, and applying insecticides. Cultural control involves maintaining healthy plants through proper irrigation, fertility, mulching, and pruning, which are important in minimizing ‘stress’, and may possibly decrease susceptibility. In addition, removing weeds attractive to Japanese beetle adults such as smartweed (Polygonum spp.) may help to mitigate infestations. Physical control involves hand removing or collecting Japanese beetle adults from plants before populations are extensive. The best time to remove or collect adults is in the morning when ambient air temperatures are typically ‘cooler.’ Adults can be collected by placing a wide-mouthed jar or bucket containing rubbing alcohol (70% isopropyl alcohol) or soapy water underneath each adult, and then touching them. Adults that are disturbed fold their legs perpendicular to the body, fall into the liquid, and are subsequently killed. This procedure, when conducted daily or every-other-day, for at least three weeks, particularly after adult emergence, may substantially reduce plant damage.
Fig 6. Floral Food Lure (Bottom) & Synthetically-Derived Sex Pheromone (Top) Associated W Japanese Beetle Trap (Auth–R. Cloyd, KSU)
The use of Japanese beetle traps in a landscape or garden is not recommended since the floral lure and synthetically derived sex pheromone (Figure 6) may attract more adults into an area than would ‘normally’ occur. Japanese beetle adults may also feed on plants before reaching the traps, which increases po
tential damage.
Spray applications of contact insecticides will kill Japanese beetle adults. However, repeat applications are required; especially when populations are excessive. Several pyrethroid-based insecticides; such as those containing permethrin, bifenthrin or cyfluthrin as the active ingredient, will suppress Japanese beetle adult populations. However, these insecticides will also directly harm many natural enemies (parasitoids and predators) and continual use will result in secondary pest outbreaks of other pests including the twospotted spider mite, Tetranychus urticae. Furthermore, these insecticides are directly harmful to honey bees and bumble bees. Therefore, apply insecticides in the early morning or late evening when bees are less active. In general, systemic insecticides are not effective against Japanese beetle adults because they have to feed on leaves and consume lethal concentrations of the active ingredient to be negatively affected. In addition, if extensive populations are present, plant damage can still occur.
The management of Japanese beetle adults requires diligence, patience, and persistence, to prevent adults from causing substantial damage to plants in landscapes and gardens.
For more information on how to manage Japanese beetle refer to the following extension
publication:
Japanese Beetle: Insect Pest of Horticultural Plants and Turfgrass (MF3488 March 2020)
https://www.bookstore.ksre.ksu.edu/pubs/MF3488.pdf