Beetles spend the winter as adults in leaf litter at the base of scale-infested plants. They become active and feed on scales when temperatures exceed 50F in the spring. Adults lay bright orange eggs, singly or in small groups under the scale covers. Eggs hatch into brown larvae covered with black spines. Larvae will flip over or chew through scale covers to feed on the fleshy scale body. After 3 larval stages larvae move to the underside of a leaf or to a crack or crevice on a twig or branch. There they become immobile and the larval skins split to form pupae. In the laboratory it takes about a month to mature from egg to adult. In the midwest during the growing season there are usually 3 generations.
C. kuwanae is noted for its voracious appetite. Each larval C. kuwanae must feed on over 100 scales to become an adult. In the United States this appetite has caused the beetle to rapidly deplete the euonymus scale population at landscape release sites. Like many other lady beetles, C. kuwanae just flies away when food gets scarce. However, other scales, such as San Jose scale, can also serve as a host (see MBCN Vol 1, No. 1).
C. kuwanae is common throughout China, Korea and Japan where it helps to keep several species of armored scales under control in citrus groves and on landscape shrubs. C. kuwanae has now been released by the USDA in most states east of the Mississippi River, five states in the central U.S. and in California. Field surveys show that C. kuwanae is widespread from Alabama to southern New England and westward to the Appalachian mountains. Presently, you can't buy this predator to release in your backyard. In areas where this beetle is established you can help it along by leaving leaf litter on the ground so that beetles have a safe place to spend the harsh midwestern winters. Despite reductions in numbers due to the exceptionally cold winter of 1993-94, some beetles survived where temperatures dipped to -27F. In addition, you should adopt standard practices that conserve natural enemies. In the landscape this means limiting pesticide use and using materials with short residual toxicities, such as horticultural oils or insecticidal soaps, when pesticides must be applied.
- Cliff Sadof, Purdue University
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