Article written by Madeline Wimmer, UMN Extension Fruit Production Educator.
Image: Japanese beetles have a wide host range and are a common pest of grape leaves in Minnesota and the Upper Midwest.
I spotted my first Japanese beetle for the year in SE Minnesota on Tuesday 06/30. Japanese beetles have been an invasive pest in Minnesota since the late 1960s and have increasingly become a pest in vineyards for the past 10-15 years. They have over 300 known host plants, commonly impacting the foliage and occasionally fruit for some crops like peaches and raspberries.
Even though many grapevines can withstand a certain amount of defoliation from Japanese beetles, early management is often important. Japanese beetles create a positive feedback loop as foliar damage increases, which releases volatile organic compounds. Additionally, as more beetles gather and begin to mate, their pheromones continue to attract more beetles on site. Adult grapevines can usually handle feeding better than young, or establishing vines. For example, I witnessed near complete defoliation of a number of vines at a research station previously, which stressed the vines to the point that they began growing shoots from their lateral buds that should have remained dormant until the next year.
Images: Japanese beetles showing deep skeletonizing of grape leaves (top) and a photo showing lateral bud growth after severe Japanese beetle damage on a young vine (bottom). Photos taken in Columbia, MO, 2017.
Females that are ready to lay eggs drop to the ground, which allows grubs to hatch, feed in the soil, and overwinter. Adult beetles can emerge from the soil on site, but a large portion of beetles may also fly in from surrounding areas as they are strong fliers capable of traveling a mile or more depending on the conditions.
Japanese beetle traps can be used to monitor for the first beetle arrival, but are recommended to be removed after the first beetles are caught to prevent attracting more beetles into the area. They should also be strategically installed away from a vineyard site. Some research has been done to study the efficacy of specific trap-and-kill options for Japanese beetles, but current recommendations are to use traps for monitoring alone. For more information related to Japanese beetle management in grapes, refer to the Midwest Fruit Pest Management guide grape section, starting on page 167.
The winsome fly and Japanese beetles
Image: Japanese beetle adults will continue to feed as winsome fly eggs are laid on their thorax. The larval feeding eventually kills the Japanese beetle, which disrupts egg-laying in female beetles.
While you’re out managing Japanese beetles this year, you might take note if you see any beetles with one or more white dots on their green middle section (thorax). These are eggs of the winsome fly (Istocheta aldrichi), a tachinid fly that is a parasitoid* of Japanese beetles.
It only takes a few days after eggs are laid for a larva to hatch and begin feeding and progressing through its larval stages. This damage does not cause instant death, but slowly deteriorates the Japanese beetle's abilities until it dies. Around this time, the larvae pupate within the beetle and overwinter until the following June.
The increased activity and parasitism by the winsome fly on Japanese beetles in Minnesota is an example of natural biocontrol and one of a few ecological impacts that has led to some natural control for Japanese beetles.
For more information on the winsome fly, check out the following resource:
UMN webpage:The Winsome Fly, Istocheta aldrichi: A unique biocontrol agent for Japanese Beetle in Minnesota
*Parasites feed from hosts, requiring that the host stay alive, whereas parasitoids like the winsome fly will typically lay eggs that consume the host as the larvae hatch and continue to develop, which kills the host.
Comments
Post a Comment