Welcome back to Ask a Naturalist: your own personal “Google” for information on all things natural on PEI. Summer is peak season for Japanese Beetles (Popillia japonica), and I’ve been getting lots of questions about this backyard pest. Let’s take a look!
If you are in the area around Cornwall, Charlottetown, or Stratford you’re probably very familiar with this insect, easily identified by its shiny, metallic, copper and green colours with white dots (hairs) along each side (photo by Alida Love, used with permission). While there have been sightings from Cavendish to Murray Harbour, Japanese Beetles are concentrated in and around the Capital region – for now.
Japanese Beetles were first discovered in North America in 1916, at an ornamental nursery in New Jersy. Given that the US had imposed import restrictions on nursery stock in 1912, it’s likely the Beetles arrived years before they were identified. Early control efforts included wide-spread spraying of cyanide and lead arsenic. Decades later, the disastrous attempt to control Japanese Beetles by indiscriminately spraying hundreds of thousands of acres with the insecticides aldrin and dieldrin – and the resulting impact on birds and other wildlife – was included in Rachel Carson’s Silent Spring.
Japanese Beetles hitch-hiked to Canada in 1939 via a tourist car travelling from Maine to Nova Scotia, with more found around Halifax-area ports in 1944. The first discovery here on PEI was at a campground in 2009. Since then, they’ve spread and increased in number to become a bane for many homeowners and gardeners.
Adult Japanese Beetles feed on hundreds of different species of plants including ornamental fruit trees, garden vegetables, and flowers (they particularly love Rose, as shown here). Eggs are laid underground in late summer and the resulting larvae feed on grass roots, leaving dead brown patches in their wake.
What can you do about Japanese Beetles? Early detection and intervention are key. Keep an eye on your plants and act as soon as you spot any Beetles; preventing an infestation will be easier than controlling it later. You can pick, vacuum, or shake Beetles off your plants and drop them into a bucket of soapy water to kill them. It’s important not to squash them: that will release pheromones and attract more Beetles. Pheromone traps are commercially available to deal with larger outbreaks, though some people find those attract more Beetles to the area. Dead Beetles can be put in a sealed clear plastic bag in your waste bin (or fed to your chickens or ducks if you happen to have any!).
If you’re seeing Japanese Beetles now, your lawn will be home to their larvae this fall. Watch for patches of dead and dying grass and pull up a piece to look for the C-shaped white grubs with a yellowish head. Beneficial nematodes (tiny invertebrates) are available at local garden centres and can be applied in early fall or early spring to kill those larvae.
Researchers are looking into additional options for biological control including bacteria and insects; the parasitic Winsome Fly may be approved for release on PEI in coming years. Whatever control options you choose, it helps to make it a community effort. Japanese Beetles do fly, and taking action on your own property can have limited success if this pest is left unchecked nearby. It’s also a good idea to check any plants you’re bringing home (from a garden centre or plant swap for example) to be sure you’re not unintentionally introducing Beetles to your property.
Japanese Beetles are almost certainly here to stay, but patience, persistence, and fighting them at both the adult and larval stages can help keep them under control. The PEI Invasive Species Council is an excellent resource, and their website has additional information for property owners.
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