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CAROLINA ™ Teamed with Teachers The Convergent Lady Beetle Introduction Throughout the world the lady beetle has been a symbol of good luck. American pioneers believed that it was good luck to have the lady beetle hibernate inside their log cabins. The Swedish believe that the number of spots on a lady beetle is an omen prophetic of the coming harvest—fewer than seven spots predict a good harvest, while more than seven foretell famine. Some Greeks believe that finding a lady beetle inside the house predicts the birth of a son; killing the beetle results in the child being born a girl. In Yugoslavia, the beetle is the bearer of good news. Other mystical properties associated with these insects include warning of danger and forecasting of weather. To some, the beetle is also a love oracle and a bringer of new clothes. The truth about lady beetles is that, while they cannot predict the future, they do bring “good luck” to man in the sense that they feed on a number of insect pests injurious to crops. The Coccinellidae The common names lady beetle, ladybird beetle, ladybird, and ladybug actually refer not to one, but to several species of beetles in the family Coccinellidae (from Gk kokklvos, meaning scarlet and referring to the color of the adults of some species). The Coccinellidae is a large family containing about 3000 species. Some coccinellids are serious crop pests (e.g., EpiIachna varivestis, the Mexican bean beetle); however, most are predacious and are considered quite beneficial. The vedalia lady beetle, Rodolia cardinalis, is a famous example of the successful use of an insect to biologically control an insect pest. This predator is credited with saving the citrus industry in California by controlling the cottony cushion scale. Morphology Like many beetles, the lady beetle has hard wing covers known as elytra. The elytra are actually the first pair of wings which have been modified in form and function so they no longer resemble wings. The elytra’s function is no doubt to protect the soft abdomen and underlying second pair of wings. While in some species (e.g., lady beetle) the elytra can be lifted and used as airfoils in flight, in many species the elytra are fused into one piece. Such beetles cannot fly, but probably are better protected. As is typical of Coleoptera, the mouthparts of the lady beetle are of the chewing type. The heavy mandibles are well constructed for grasping, killing, and chewing prey. The majority of lady beetles feed on soft-bodied insects, particularly aphids and coccids. 2 Life Cycle The convergent lady beetle (H. convergens) is primarily an aphid predator and has been a popular biological control for aphids since 1912. Its popularity has no doubt been due (at least partially) to the ease of collecting and storing this species. The life span of H. convergens is one year. Eggs, which are laid in the spring, develop into darkish gray larvae with orange spots. These soft-bodied, carrotshaped, spiny larvae appear quite unlike the round, hard-bodied adults, yet both have a voracious appetite for aphids. It has been claimed that the convergent lady beetle is capable of eating more than 50 aphids a day when actively feeding. The pupae of H. convergens, as is typical of coccinellids in general, do not spin cocoons, but are naked. They attach themselves to a leaf by cementing the tip of the abdomen to the leaf. When disturbed, the pupae have the habit of lifting the body to a vertical position, then dropping back down again. This behavior may have a protective function by discouraging predation or parasitism of the exposed pupae. During the first week in June, new adult beetles appear. They are active crawlers and fliers and can disperse nearly 5 miles in as little as 3 days. Throughout the spring and autumn, adults are abundant in the fields. However, as winter approaches they migrate to the mountains where they congregate in large numbers prior to winter hibernation. For example, in the Sierra Nevada Mountains of California, literally thousands of adult beetles assemble before moving off to hibernate under nearby leaf litter and stones. It is from these aggregations that the beetles can be easily collected. For about 9 months while in the mountains, the adults do not feed but live off stored fat. The ability to undergo long periods of fasting under cool temperatures has allowed man to conveniently store H. convergens under refrigeration (5–8ºC) for months. The beetles that Carolina Biological supplies can be satisfactorily held in the refrigerator until spring, when they should be released in the garden. Providing a vial of water and a vial of sugar water, each with a cotton wick, may help the survival of the beetles during refrigeration. Beetles received after the last frost but before June should be released immediately and not stored in the refrigerator. At this time they have used up their stores of fat and need to begin actively feeding. 3 Further Reading DeBach, Paul, “Biological Control by Natural Enemies”, Cambridge University Press, London, 1974. Essig, E. D., “College Entomology”, Macmillan Company, New York,1954. To order call: 1-800-334-5551 (US and Canada) 336-584-0381 (International) For technical help call: 1-800-227-1150 Carolina Biological Supply Company 2700 York Road, Burlington, North Carolina 27215 CB130519806