Japanese Beetles: Insects with Expensive Taste

Japanese beetles were introduced into North America on nursery stock from Japan in 1913. They have become seasonal pests of many crops including tree fruit and berries. Of particular concern to apple growers is their attraction to young plantings of “Honeycrisp” apples—a variety which is being planted more and more in Ontario, and is providing growers with good returns.

Injury from Japanese beetles is beginning to appear in some orchards. While feeding on apples is usually concentrated on the foliage, fruit feeding can occur in stone fruits, especially as they ripen or where other surface damage is present. This year it appears that Japanese beetles have a distinct preference for plum foliage (Figure 5) over nearby peaches and pears. Clusters of feeding (and mating) beetles are also easy to find on ripe, damaged peaches. Although the beetles’ habit of aggregating on damaged fruit sometimes means that less fruit overall are attacked, even the smallest blemish or bird peck is enough to start a feeding frenzy. Field workers and the public are also annoyed or alarmed at the beetles defensive posture (legs outstretched and waving) and their habit of flying straight at whatever disturbs them.

Adults beetles are 10-13 mm long, metallic green to greenish-bronze, with coppery red wings and small white tufts on the sides and tip of their abdomen (Fig 4). Adults feed on the upper surface of apple foliage, chewing the tissue between the veins, creating a skeletonized appearance (Fig 5). Beetles usually feed in groups starting at the top of the plant and moving downward. They can fly as far as 8 km, but usually only make short flights as they move around to feed and lay eggs. Japanese beetles produce aggregation pheromones that attract more males and females to feed and mate. Odours emitted from damaged plants may also attract more beetles into the orchard.

Adults begin emerging in late-June to early-July and they will live for 30 to 45 days. Females lay 40 to 60 eggs in the soil during July and August, and the larvae hatch in 10 to 14 days. Larvae are “C” shaped, white to cream-coloured grubs with brown heads. The grubs feed on organic matter and grass roots prior to moving into over-wintering sites.

In most years, sprays for Japanese beetles are not necessary in apple orchards, but in orchards where populations are high and the insects are feeding on susceptible varieties (“Honeycrisp”) or on immature trees, control measures may be necessary. Imidan (phosmet) is registered for Japanese beetle on tree fruit but note that the spray solution must be at pH 5.5 to 6.5 for best results. The application of a pyrethroid, or Assail to manage other pests may also control Japanese beetle. The tendency of beetles to feed at the top of trees makes good coverage essential for adequate control. The migration of these insects into orchards from surrounding areas may make multiple applications necessary.

Japanese beetle traps are available at garden centers. Although the pheromone and floral lures sold with the traps are very effective and can attract many beetles each day, research has shown that the traps attract more beetles than are caught. As a result, susceptible plants in the vicinity of the trap are likely to suffer more damage than if no traps were used.

Figure 4 - Adult Japanese beetles on raspberry leaf.

Figure 5 - Foliage at top of plum tree skeletonized by Japanese beetles.