The Japanese beetle (JB; Figure 1), an invasive insect pest that can cause economic damage to several fruit crops, started showing up in large numbers here in Wisconsin in the past 3-4 weeks. JBs feed on the leaves of over 300 plant species and can be difficult to manage due to their high mobility and dense numbers. Current control strategies focus heavily on insecticides, with many fruit growers making multiple spray applications to control this pest throughout the summer months. Insecticides should be used minimally, as applications pose risks to non-target insect species (Serrão et al. 2022), have environmental and social impacts, and can lead to resistance from insect species to insecticides (Forgash 1984). For growers hoping to reduce or avoid insecticide applications, there are a few other management strategies for Japanese beetle that should be considered.
When few beetles are present in the crop or are present in isolated patches, hand picking is an effective control method. Collecting is best done in the morning or evening when temperatures are cooler, and the beetles are less active and thus easier to collect at these times. Once the beetles are collected, they can be killed by placing them in soapy water. This strategy requires frequent collecting, as adults are very mobile and will continue to show up for most of the summer months. This strategy will work mostly for small areas.
Japanese beetle traps
Traps for Japanese beetle can easily be purchased at many retail stores or online at places such as Great Lakes IPM. These traps are baited with lures that consist of floral and sometimes also sex pheromone lures. These lures are able to attract the Japanese beetle from long distances, and often are able to collect many beetles very quickly. Traps are sometimes avoided by growers because they can lure JBs in from long distances, potentially bringing in more beetles than they actually kill, and because JBs often congregate around the traps. Thus it is often recommended to place the traps several yards from crops. Recently, research has looked at using these traps in a mass trapping approach, implementing a large number of traps either along the perimeter or inside fields. This approach is still being assessed to determine whether it lures in more beetles than it kills within an area.
For smaller fruit crops, a physical barrier can be used to keep adult JBs from feeding on leaves. Row covers consist of fabrics which cover the entire plant and can exclude adult JBs and other insects. These are typically applied July through August, when JB numbers are highest. Row covers may be expensive and are time consuming to apply but work well at preventing leaf damage by JB.
Entomopathogenic nematodes are microscopic worm-like organisms that can be used as a biological control agent for JB larvae. Nematodes have been shown to reduce the number of larvae within an area by penetrating the larva’s body, and infecting them with a bacteria that eventually leads to death. Nematode applications can reduce the larval population in an area by up to 90% in a year (Klein and Georgis 1992). Applications of nematodes are made directly to moist soils in the morning or evening. Managing for JB larvae at this small scale is often unsuccessful at reducing the number of adults, as the adults can travel far from where their larval stage occurs, and become pests even in areas where larval numbers have been reduced.
Bacteria alone also serve as a biological control agent. Milky spore disease is already present in soil killing many larvae, but additional applications seem to be unsuccessful at reducing larval populations (Redmond and Potter 1995). Another bacteria, Bacillus thurigiensis (Btj and Btg), can be used to kill larvae, with Btg also able to reduce adult feeding when applied to the leaves of crops (Redmond et al. 2020, Althoff and Rice 2022).
Native insect pests of JB are another form of biological control, and have been released in the United States in an attempt to reduce their numbers. Two parasitoid wasps, T. vernalis and T. popilliavora, both are able to seek out the JB larvae and lay their eggs inside them, ultimately killing the larvae. A fly, Istochetaaldrichi, has also been released and lays its eggs directly on the adult beetles. When the eggs hatch, they burrow into the beetles and eventually cause death. Growers can support populations of parasitoid insects by maintaining a healthy array of native plants and insects (Althoff and Rice 2022). Overall, biological control for JB can help reduce localized populations but the success of these strategies will depend on the size of the populations flying into attractive agroecosystems from the surrounding landscape.
Happy growing season and may the Japanese beetle numbers be low this year!
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Redmond CT, Wallis L, Geis M, Williamson RC, Potter DA. 2020. Strengths and limitations of Bacillus thuringiensis galleriae for managing Japanese beetle (Popillia japonica) adults and grubs with caveats for cross-order activity to monarch butterfly (Danaus plexippus) larvae. Pest Manag Sci. 76,2:472-479. https://doi.org/10.1002/ps.5532
Serrão JE, Plata-Rueda A, Martínez LC, Zanuncio JC. 2022. Side-effects of pesticides on non-target insects in agriculture: a mini-review. Sci Nat. 109, 17. https://doi.org/10.1007/s00114-022-01788-8This article was posted in Insects and tagged Christelle Guédot, Insecticides, insects, Japanese Beetles, management without insecticides, Mitchell Lannan.