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Hippodamia convergens This is one of the best known and most common American lady beetles and is found from southern Canada to South America. This is the species sold by insectaries for aphid control.
Appearance Convergent lady beetle adults are slightly elongated in shape and can range from 4-7 mm in length. They have a prominent black and white pattern behind the head, and black spots on red forewings. Beetles may have a full complement of 13 spots or they may have only a few. The white lines that converge behind the head are common to all individuals.
Habitat (Crops) Wheat, sorghum, alfalfa, vegetables, greenhouse crops, orchard crops, and most crops attacked by aphids.
Pests Attacked Adults and larvae prey mainly on aphids. Reported prey include cotton, pea, melon, cabbage, potato, green peach, and corn leaf aphids. If aphids are scarce, beetles and larvae may feed on small insect larvae, insect eggs, mites and, occasionally, nectar, and honeydew secreted by aphids and other sucking insects. Convergent lady beetles have been recorded as predators of asparagus beetle eggs and larvae and potato psyllids.
Life Cycle These beetles can adjust their life cycle according to the availability of aphids. Resident populations in the eastern United States are active throughout spring and summer if aphids are present.
Females may lay from 200 to more than 1,000 eggs over a one to three month period commencing in spring or early summer. Eggs are usually deposited near prey such as aphids, often in small clusters in protected sites on leaves and stems. The eggs are small (about 1 mm) and spindle-shaped. Lady beetle larvae are dark and alligator-like with three pairs of prominent legs. They grow from about 1 mm to 4-7 mm in length over a 10 to 30 day period. Large larvae may travel up to 12 m in search of prey. The pupal stage may last from three to 12 days depending on the temperature. One to two generations occur each year, depending on the length of the season, before the adults enter winter hibernation, usually in a protected site. Development from egg to adult may take only two to three weeks, and adults live for weeks or months, depending on the location, availability of prey, and time of year. In the western United States, adult convergent lady beetles typically spend up to nine months, from May to February, hibernating in large aggregations in mountain valleys, far from potential food sources. In spring, the adults disperse in search of prey and suitable egg laying sites. This dispersal trait is especially strong in H. convergens.
Pesticide Susceptibility Tolerance to some pesticides at recommended application rates is likely. Overwintering adults may be less susceptible than active adults and larvae.
Conservation Whenever possible, conserve local populations by minimizing the use of broad-spectrum insecticides, providing refuges for shelter and overwintering, and following other integrated pest management guidelines as outlined in the introduction to this guide. For general information about conservation of natural enemies, see Conservation in the Tutorial section on this site, Feature Article on conservation in Volume II, No. 1 of Midwest Biological Control News.
Commercial Availability Commercial insectaries distribute beetles that have been "harvested" from natural winter aggregation sites. If lady beetles are collected in this dormant state and transported for field release, even among aphid infestations, they usually migrate before feeding and laying eggs. This migratory behavior before feeding is obligatory. Releases of such "harvested" convergent lady beetles could be a waste of time, money, and beetles. Insectaries may feed the adult beetles a special diet after they have been collected to minimize their migratory behavior. Only such preconditioned beetles should be purchased. Additionally, these harvested beetles may be parasitized. See the off-site publication, Suppliers of Beneficial Organisms in North America.
Taken from: Hoffmann, M.P. and Frodsham, A.C. (1993) Natural Enemies of Vegetable Insect Pests. Cooperative Extension, Cornell University, Ithaca, NY. 63 pp.
References Beers, E.H., Brunner, J.F., Willett, M.J., and Warner, G.M. (1993) Orchard Pest Management: A Resource Book for the Pacific Northwest. Good Fruit Grower, Yakima, WA. 276 pp. Photograph from Raupp, M.J., Van Driesche, R.G., and Davidson, J.A. (1993) Biological Control of Insect and Mite Pests of Woody Landscape Plants: Concepts, Agents and Methods. University of Maryland, College Park, MD. 39 pp. For information contact: Agricultural Duplicating Service, 6200 Sheridan Street, Riverdale, Maryland, 20737. Telephone 301-403-4264.
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