by Alida Malloy, Horticultural Research Assistant, OMAFRA
Right now, up in the tops of the canopy, leaves are being reduced to the lace-like skeletons of their veins. This skeletonization is the result of the appetite of one insect: the Japanese beetle. So, what do these insects look like? Where do they come from? And how do they impact Ontario apples?
Adult Japanese beetles are easily identifiable with their metallic green abdomen and thorax. The adult insects also have copper-coloured wing coverings and tufts of white hair down the sides and back of their abdomen. At the larval stage, they are white C-shaped grubs with brown heads and a distinctive V pattern of spines on their final segment.
As the name implies, the Japanese beetle is an invasive species native to the main islands of Japan. The first sighting in North America was in southern New Jersey in 1916. It was identified in Canada only in 1939, arriving from a Maine ferry on a tourist’s car in Yarmouth, Nova Scotia.
Since its arrival to Canada, beetle populations have been established in southern Ontario and isolated pockets of Quebec. However, its range continues to expand yearly. The climate in these regions seem to be ideal for the beetles, who enjoy a summer soil temperature between 17.5 °C and 27.5 °C, precipitation of 25 cm, and a winter soil temperature of -9.4 °C. Careful monitoring and scouting have tracked the infestations, though it has been impossible to eliminate the insect from Canada.
These insects have only a single generation per year. In summer, the adults emerge in late June and their activity peaks in late July through early August. Beetle flight peaks on clear sunny days at 21°C and at 60% humidity, though it is mostly confined to short distances. Flight is often in response to either a feeding-induced volatile emitted from a damaged plant or a highly attractive sex pheromone. This is because adults spend their days eating and mating before returning to the soil for the night.
Adult females live only 30-45 days but will lay up to 60 eggs approximately 8cm deep in moist, loamy soil covered in short grass cover or reduced-tillage crop fields, like soybean. After approximately two weeks, the eggs hatch and the small larvae feed off grass roots until cold weather hits. Then, the larva overwinter 5 to 31cm below the surface. In spring, they emerge and begin feeding again.
When fully grown, the larva pupate before resting for two weeks. After this period, adult beetles emerge to begin the cycle anew.
During both its adult and larval stage, the beetle is considered a pest in Ontario to different crops. Adults feed heavily, munching on the vegetation of over 250 plants and severely injuring elm, maple, hazelnut, grape, peach, apple and more. Beginning at the top of the canopy where the plants are completely exposed to the sun, the beetles work their way down. The insects consume the green tissue between the veins, leaving behind the distinctive, lacy skeleton. In apples, newly planted or nursery trees are particularly susceptible to Japanese beetle damage, especially Honeycrisp.
Directly following emergence, adult Japanese beetles focus on low-growing plants and after 7-10 days move onto fruit and shade trees. Severely injured leaves turn brown and drop. As the leaves become less and less attractive, the beetles move on to flowers and field crops.
In its larval state, the Japanese beetle feeds on the fibrous roots of turf, ornamentals, and vegetables. Typically, this activity peaks in August and September as damaged turf initially wilts and yellows before dying. Larval feeding is so devastating, it can mimic signs of drought.
Having non-grass cover in row middles and maintaining clean cultivating soils can discourage Japanese beetles from laying eggs in orchard systems. Clean cultivation may also expose eggs and grubs to the sun, wind, and predators by bringing them close to the surface. However, these practices do not prevent adult Japanese beetles from moving into the orchard from the adjacent landscape.
Orchards that are surrounded by naturalized landscape with wild bramble (raspberry/blackberry), Virginia creeper, or wild grape tend to have more feeding damage. Additionally, having these weeds nearby allows adults to move in and out of the crop, increasing the number of insecticide applications required to control for the pest. Removing these weeds can help reduce beetle populations on both accounts.
Overall, these beetles are an invasive pest of Ontario crops and can cause extensive damage depending on the cultivar, climate, and soil conditions. To learn more, check out the links below:
Government of Canada. (2017). Popillia Japonica (Japanese Beetle) – Fact Sheet. Popillia Japonica (Japanese Beetle) – Fact Sheet – Canadian Food Inspection Agency (canada.ca)
Kessel, C. (1992). Japanese Beetles in Nursery and Turf. Japanese Beetles in Nursery and Turf (gov.on.ca)
Klein, M. (2008). Popillia japonica (Japanese beetle). Popillia japonica (Japanese beetle) (cabi.org)
Krischik, V., Maser, D. (2005). Japanese Beetle Management in Minnesota. Japanese Beetle Management in Minnesota (umn.edu)
Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). (2009). Integrated Pest Management for Apples.