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Japanese Beetles

This has been an odd summer, as so many insects appear in perilously low numbers, while others appear in abundance. But why is it the ones that cause the most damage, or are the most annoying, are the ones that seem to dominate the invertebrate landscape?

Mosquitoes, black flies, June bugs and others seem to come back every year in good numbers, but fireflies, Mayflies, and myriad others are present but only in low numbers. The answers will remain obscure, but resiliency and adaptability are assuredly part of the reason. Did you know, a mosquito egg can last up to seven years in the soil, waiting for the right environmental conditions for it to hatch?

I wrote recently about Gypsy Moths, and we are all too familiar with the devastation that the Emerald Ash Borer caused. A new scourge visited this summer – the Japanese Beetle!

Now, they may be annoying but they are also very attractive. Related to Dung Beetles, each beetle is about 15 mm (½”) long and sports iridescent colours that inspire awe. Greens and coppers dominate the back and head of this beetle, while 5 pairs of small white and two pairs of larger white dots can be found along the edges of the wings and abdomen.

First reported in North America in 1916 in the USA, they spread slowly to Canada in 1939 into Nova Scotia, and from there the rest is history as they can be found across most of Canada and the USA! So let’s explore their life cycle a bit.

The female lays her eggs (40 to 60) in shallow soil singly or in small bunches which hatch in about 2 weeks and the larvae start feeding. They will go deeper into the soil for the winter, where they hibernate until the soil temperatures rise in the spring. Then the larvae (that look like small white grubs) burrow upward to shallower soil and continue feeding on grass and plant roots. After 4-6 weeks they have grown substantially and enter their pupal stage, where they will transform into adult beetles.

While the larvae may do significant damage to turf, the adults are known to attack over 300 species of plants as they feed on the leaves and fruits of many species. They are known as skeletonizers, which simply means they feed on the soft tissue between the veins in the plants leaves. For the next 4-6 weeks, the beetles can be found in large numbers on favoured plant species.

In my garden they love our raspberries, but ignore many others species growing nearby such as highbush cranberry and tomatoes. It is during this time the females emit pheromones which drive the males crazy! They swarm to the females to copulate and then wait for another opportunity, while snacking on our plants in the interim!

So what can you do? I personally don’t like broadcast pesticides and prefer to try to solve the problem in a more environmentally sensitive way. In my case, I only have a few (<100) so I pick them off individually and put them in a coffee jar for a bit and after they’re ‘subdued’ I put the carcasses in our small pond, and the three small Painted Turtles who live there come to eat them for dinner. Seems like a win-win!

If you have a bigger issue or they are causing serious damage, there are several traps available at local stores. These use artificial hormones to attract the males to the trap. Recent research, however, indicates these lures may in fact worsen the problem locally, as the beetles come to the area in response to the bait but then stop short of entering the trap and feed on adjacent plants.

Even though this species is not native to North America, a disease that controls them has emerged. Called Milky Spore Disease, it is fatal to them. Companion planting with repellent plants can be effective. Try garlic, chives, tansy or catnip as they can provide some relief. Nature is beautiful but can be a bit annoying!

Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on LinkedIn and Facebook.

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