The Spotted Cucumber Beetle
The spotted cucumber beetle (Diabrotica undecimpunctata) is expanding its range northward along the Front Range. Also known as the Southern Corn Rootworm, it feeds on a wide variety of plants, and is a significant problem for cucumber and cantaloupe, as well as beans and corn. Adults are one-quarter inch long, yellow-green, with 12 black spots on their wings.
In years where populations of this insect are high, adults can be found feeding on ornamental plants as well as vegetables, and can damage flowers, new shoots, and stems. Females prefer to lay eggs in moist soil cracks, where larvae develop by feeding on roots of host plants. They reach maturation in approximately one month from hatching. Two to three generations are produced each season. If soil moisture and fertility are adequate, the root feeding does not significantly stunt affected plants.
Adults feed on the blossoms of as many as 200 alternate host species. Because scarring of flowers may occur from adult feeding, blossoms for market should be protected with floating row covers prior to July, when migrating adults first arrive. If row covers are not practical due to pollination requirements, applications of insecticides can be used to control foliage and flower feeding insects.
Heavy layers of mulch around host plants can prevent adults from inserting eggs into the soil, and research in Virginia (Caldwell and Clark, 1998) suggests that aluminum coated plastic mulch effectively repels spotted cucumber beetles. Meticulous cleanup and disposal of debris is crucial to removing over wintering insects.
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Updated Tuesday, October 13, 2015