Hosts or Prey
Egg-sac producing mealybugs and scales and especially cottony cushion scale, Icerya purchasi
Identification
Adult vedalia (lady beetles, also called ladybugs or ladybird beetles) are about 1/8 inch (3 mm) long and irregularly marked with black and red. Black predominates on some individuals and red on others. Overall this lady beetle can appear grayish because it is covered with fine hairs. Adults are dome shaped (convex) on top, flat on the bottom, and oval when viewed from above.
Eggs are oblong and red. They are most readily observed when laid on the white egg sac of cottony cushion scale.
First instars (immatures) have a red body, red legs, and no obvious antennae. Second instars have dark reddish to black legs and black tubercles (slightly raised bumps) on the abdomen and thorax. Third and fourth instars have black legs and more apparent black tubercles. Their body is dark pink, but can appear bluish to gray overall. Fourth instars grow to about 1/4 inch (6 to 7 mm) long before pupating.
The mature, fourth instar glues itself to a leaf or twig before pupating. The pale skin of the fourth instar splits over the back to reveal the developing, oblong pupa. A healthy pupa is reddish and moves slightly when touched.
Lookalikes
Adults because of their unique coloration are unlikely to be confused with other lady beetles in California. First instars resemble the crawlers of cottony cushion scale; both are reddish and oblong and can be observed on the egg sacs of cottony cushion scale. However, cottony cushion scale crawlers have black legs and black antenna that commonly project forward; vedalia first instars have red legs and no obvious antennae.
Life Cycle
Vedalia develops through 4 life stages: egg, larva, pupa, and adult. Females can lay several hundred eggs during their 1 to 3 month lifespan. Larvae develop through 4, increasingly larger instars. Vedalia can develop throughout the year in coastal areas. Development from egg to adult occurs in 4 to 6 weeks when temperatures are warm. Vedalia has multiple generations per year.
Habitat
Adult females lay eggs singly or in a scattered group attached to the egg sac of cottony cushion scale. The first instars dig their way into the egg mass and feed mostly hidden on the eggs. Second through fourth instars are active searchers that move on leaves and up and down branches searching for and feeding on all stages of the scale.
Vedalia is the most important natural enemy of cottony cushion scale in California's Central Valley. In coastal locations a tiny, parasitic, black fly Cryptochaetum iceryae is the most important natural enemy of cottony cushion scale. Both natural enemies can be common at intermediate locations, such the delta regions of the Sacramento and San Joaquin Rivers.
If its populations are not disrupted by pesticide application or hot weather, when vedalia adults arrive in Central Valley citrus orchards in March to April they can control a serious cottony cushion scale problem in 4 to 6 weeks. Vedalia halts egg production and larval development slows when daily temperatures exceed 90°F, usually in June in the San Joaquin Valley.
Species
Two Novius species occur in California, N. cardinalis and N. koebelei. Both were introduced from Australia in the 1880s when the genus was named Rodolia. These lady beetles successfully control cottony cushion scale that was killing trees in commercial citrus orchards. Novius cardinalis (vedalia) is the more common and important predator.
Novius koebelei has wing covers that are black, red, yellow, or a mix of these, varying among individuals. Unlike vedalia, N. koebelei lacks a black, longitudinal stripe on top where the wing covers meet. No other red and black lady beetles marked similarly to vedalia occur in California.
More Information
- Bioecological and Population Studies of the Cottony-Cushion Scale, Icerya purchasi Mask., and its Natural Enemies, Rodolia cardinalis Mul. and Cryptochaetum iceryae Will., in Southern California, Hilgardia
- Conserving Vedalia Beetle, Rodolia cardinalis (Mulsant) (Coleoptera: Coccinellidae), in Citrus: A Continuing Challenge as New Insecticides Gain Registration, UC Riverside, Journal of Economic Entomology
- Cottony-Cushion Scale, Icerya purchasi Maskell - Homoptera, Margarodidae, UC Riverside
- The History of the Vedalia Beetle Importation to California and its Impact on the Development of Biological Control, UC Berkeley, Annual Review of Entomology
- Protecting Natural Enemies and Pollinators, UC Integrated Pest Management Program
- Stages of the Cottony Cushion Scale (Icerya purchasi) and its Natural Enemy, the Vedalia Beetle (Rodolia cardinalis) (PDF), UC Agriculture and Natural Resources
- Vedalia Beetle, Rodolia cardinalis, Coleoptera: Coccinellidae, UC Irvine
Scientific classification:
- Phylum: Arthropoda
- Class: Insecta
- Order: Coleoptera
- Family: Coccinellidae
