Tortoise beetles in gardens
Tortoise beetles are small (about 1/4 inch long), round, turtle-like insects. They have thin margins that extend out from their body as well as a shield-like structure that covers their head. Tortoise beetles vary in color, some are dark while others have bright metallic colors. Tortoise beetles are one of the few insects that can change their metallic colors. Their larvae are interesting because they glue caste skins, debris, and excrement together and hold it over their back like an umbrella. They stick this material at potential predators to protect themselves.
Tortoise beetles are a type of leaf beetle and feed on the foliage of various plants. Although their can feeding can be potentially severe, they are seldom reported as a problem in gardens here in Minnesota. The tortoise beetle, Plagiometriona clavata has been reported recently on Chinese lantern. It is also reported in the literature to feed on jimson weed, Datura stramonium and (presumably) other members of the Solanaceae. They chew round holes in the leaves, although submitted samples showed only minor to moderate damage. There have been other reports of tortoise beetles this summer on various garden plants. Different species are known to feed on plants in the morning glory family (Convolvulaceae).
For the most, this damage is not important, especially this late in the summer. Tortoise beetles damage is rare in Minnesota gardens. If it's necessary, hand pick small number of these beetles. If large numbers are present and control is desired, use a residual insecticide (e.g. permethrin, acephate, carbaryl).
Published in Yard & Garden Line News, September 1, 2000