Golden Beetles in Your Garden

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Golden tortoise beetle (Charidotella sexpunctata). Photo: Ilona Loser, Wikimedia Commons

Arguably the shiniest insect you’ll ever see, the golden tortoise beetle (Charidotella sexpunctata) really does look as if it was made of gold. The adult, about ¼ inch (5 to 8 mm) long, resembles a domed transparent oval shield under which there is a brilliantly glossy golden insect. When it feels threatened, it pulls back inside its dome, hiding its legs and antennae underneath, like a frightened tortoise hides in its shell. Hence the name: golden tortoise beetle.

If you disturb a golden tortoise beetle, it will lose its golden shine. Photo: inaturalist.ca

This insect is strikingly beautiful: it looks like a small gold brooch! But in case you were considering wearing at your next gala, you need to know that if you touch a golden tortoise beetle, the gilding will disappear, revealing a rather ordinary beetle, reddish orange with six black dots (the meaning of sexpunctata), somewhat like a rather elongated ladybug.

The bright golden color comes from a liquid layer that thins out (revealing the true color of the insect) or thickens (restores its gilding) depending on the conditions and the state of mind of the beetle. When it is too scared, for example, the liquid thins and the gilding disappears.

Wide Distribution on Two Continents

Map showing the beetle’s distribution in Canada and the United States. Photo: inaturalist.ca

Sorry, but if you don’t live in the New World, you won’t be seeing this the golden tortoise beetle in your garden, but it is widely distributed in both South and North America, from Argentina to Canada.

Ornamental sweet potato pitted with beetle holes. Photo: Frances Washington, http://www.hometalk.com

And it really is essentially a garden insect, because its favorite hosts are plants in the morning glory family (Convolvulaceae), some of which are popular garden plants. So, if you find the leaves of your sweet potatoes (Ipomoea batatas), both those grown for their colorful foliage and those grown for their edible tubers, and of your morning glories (I. nilI. purpureaConvolvulus tricolor and others) pierced by small holes, it’s probably the work of the golden tortoise beetle.

It also lives on wild Convolvulaceae plants, in particular bindweeds, including the widely distributed weeds hedge bindweed (Calystegia sepium) and field bindweed (Convolvulus arvensis). In fact, they are often its main host plants early in the season, before sweet potatoes and morning glories have been planted. It also sometimes settles on certain field weeds from other families (burdock, thistle, nettle, plantain, etc.) at that time, but still needs a morning glory relative of some sort to complete its cycle.

Life Cycle

Adults overwinter in plant debris, coming out in spring to lay their eggs in groups, usually under the leaves of wild bindweeds.

The dung-covered larvae are distinctly unappealing. Photo: http://www.jungledragon.com

To the north of its range, the larvae emerge in late May or early June and start to eat the leaves from below, often leaving only the veins. The larvae are not golden, but brown to yellowish, surrounded by fringes, and cover themselves with their dead skins and excrement to protect themselves from predators. There is certainly nothing appealing about those!

After a few weeks, they settle down under a leaf and pupate, then the adults emerge about a week later. The adults are winged and mobile, tracing suitable host plants by their smell.

Adults also eat Convolvulaceae leaves, but tend to do less damage than the larvae. True, they do make plenty of holes when there are a lot of them, but rarely do you see them cutting the leaves into shreds like the larvae often do. The adults continue to eat holes in leaves here and there all summer, then go into dormancy in the fall. There is only one generation per year.

Beetle Control

A few holes in the leaves don’t stop morning glories from flowering. Photo: Megan Brown

It must be said that, despite the holes in the leaves, the golden tortoise beetles don’t really seem to seriously harm their host plants. They usually continue to grow vigorously despite the predation, flowering normally (morning glories and bindweeds) or producing goodly numbers of tubers (sweet potatoes). So, if a few leaves looking they were hit with gunshot don’t bother you, you can just let the beetles live out their lives.

If you want perfect leaves, though, you’ll have a bit of work to do.

First, reduce their number by eliminating bindweeds from in and around your garden. And always carry out crop rotation, avoiding planting Convolvulaceae species in the same place two years in a row. If you’re treating sweet potatoes as a vegetable, using floating row cover as an exclusion barrier is very effective, but it makes little sense to cover ornamental sweet potatoes and morning glories with fabric, because that will hide from view a plant grown specifically for its beautiful appearance.

Also, you can treat larvae (on the underside of leaves) and adults by spraying them with a soap-, neem- or pyrethrum-based insecticide. Or just check your plants regularly, dropping any golden tortoise beetles into a bowl of soapy water.

________

The golden tortoise beetle: a jewel of an insect, but it does have its share of flaws. But then, what did you expect? Haven’t you heard that all that shimmers isn’t gold?

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