Over the winter of 1888-1889 a lady beetle called vedalia beetle was introduced into California from Australia to combat cottony cushion scale, Icerya purchasi - also an introduced species. Cottony cushion scale was causing infestations so severe in California citrus groves that growers were pulling out their trees and burning them. Orchard values were plummeting. Yet, by the fall of 1889, the pest was completely controlled in the areas of introduction. The vedalia beetle literally saved the California citrus industry, and since the California success, it has been exported to many other parts of the world, often with equally successful results.
The introduction of the vedalia beetle is considered to be the beginning of classical biological control. The interest of scientists, growers and the public in this project was due to its spectacular success which was striking because the financial threat to the California citrus industry was acute; the pest itself was showy and its damage was obvious and critical; growers took the initiative and applied the natural enemies themselves; the natural enemies were visibly voracious and active; and the destruction of the pest and the recovery of the trees was evident within months. The cost of the project was about $1500.
Adults are very small, densely pubescent, red and black lady beetles, about 2.5-4 mm (1/16-3/16 inch) long. Eggs are red, young larvae are reddish, and pupal cases are whitish.
Acacia, boxwood, citrus, magnolia, Nandina, olive, Pittosporum, and rose - all species attacked by cottony cushion scale. The vedalia beetle is established in California and Florida and may also be found in disjunct locations of the southern U.S.
R. cardinalis is specific to cottony cushion scale. Adults and mature larvae feed on all scale stages; young feed on eggs.
Adult beetles lay eggs underneath the scale or attached to scale egg sacs. There are 8 generations per year in the cooler coastal areas of California, and 12 generations per year in the hot, dry inland areas. A female will lay from 150-190 eggs during her lifetime.
Together with an imported parasitoid, Cryptochetum iceryae, Rodolia cardinalis keeps California populations of cottony cushion scale at extremely low levels in orchards and on ornamentals.
The original 514 beetles imported over the winter of 1888-89 multiplied so quickly that by June 12, officials were able to distribute10,555 vedalia beetles to 208 growers around the state. The rapidity and extent of the subsequent control was reported to be nearly unbelievable. One grower who had abandoned hope for his young orange trees was able to harvest two to three boxes of oranges from each tree at the end of the season in 1889. By October, it had become very difficult to find a living specimen of Icerya in the vicinity of Los Angeles, the area where the introductions were made.
Many diverse climates have become home to beetles descended from those introduced to California. From the original 514 individuals, thousands of beetles have been sent to other locations around the world. In one instance, 3 individuals from Italy, also descendants of the California beetles, provided the genetic basis for a population established in France. (This population was later augmented with more beetles from Italy, California, and Portugal.) The California population is the sole basis for colonies established in Egypt, Cyprus, the Soviet Union, Portugal, Puerto Rico, Venezuela, Peru, Chile, Hawaii, the Philippines, Guam, Uruguay, Argentina, Taiwan, and Palau, suggesting this population has an enormous ability to adapt.
The vedalia beetle is very sensitive to Baythroid, an insecticide being used for citrus thrips control. Baythroid kills the beetles and prevents them from laying eggs for about one month. In contrast, some other insecticides used for citrus thrips control, Veratran, Agri-Mek, and Success do not seem to have any noticeable effect on vedalia beetles. The vedalia beetle is also very sensitive to the new insect growth regulators, Esteem (=Knack, pyriproxifen) and Applaud (buprofezin), which are applied for California red scale control. The insect growth regulators prevent vedalia from pupating and emerging as adults and in the case of Esteem they prevent the adults from laying fertile eggs.
Orchards adjacent to orchards sprayed with growth regulators had severe cottony cushion scale problems in 1998 and 1999, indicating the beetles are extremely sensitive to these pesticides either because of drift or because the beetles are moving in and out of treated orchards. The effects of the insecticides are long lasting (4-6 months). After sprays were applied in the summer of 1998, live vedalia beetles could not be found in the San Joaquin Valley of California for 9 months. After fewer sprays were applied in the summer of 1999, live vedalia were found in the fall of 1999 in many orchards. Researchers at the University of California Kearney Agricultural Center are conducting experiments to learn how to rear vedalia beetles so that they can be released in problem orchards and are continuing to study in detail how the insect growth regulators affect vedalia.
Over the years, there have been other times that vedalia beetle has been eliminated from orchards by insecticide applications. During the years that DDT was used extensively, the vedalia beetle population in orchards in the Central Valley of California was decimated. It took three years for growers to modify their spray programs and recolonize their orchards with the beetle. In the meantime, some trees were killed, many orchards were defoliated by the scale, and growers paid up to $1.00 per vedalia beetle in their eagerness to re-establish the scale predator.
Vedalia beetle is not commercially available at this time.
Thanks to Beth Grafton-Cardwell for correcting an earlier revision of this page and for supplying additional information.
Caltagirone, L.E. and Doutt, R.L. (1989) The history of the vedalia beetle importation to California and its impact on the development of biological control. Ann. Rev. Entomol., 34: 1-16.
Gordon, R.D. (1985) The Coccinellidae (Coleoptera) of America North of Mexico. NY Ent. Soc. J., 93:1-912.
Grafton-Cardwell, B. (1999) "Vedalia Beetle Information – July 1999" http://www.uckac.edu/citrusent/vedainfo.htm
DeBach, P. (1974) Biological Control by Natural Enemies. Cambridge University Press, New York. 323 pp.