Hosts or Prey
Scale insects mostly, but also other plant-sucking insects formerly called Homoptera
Identification
Adults of these lady beetles (ladybugs or ladybird beetles) are oval when viewed from above and dome shaped (convex) when viewed from the side. Their shiny body has a finely pitted surface and is covered with short, pale grayish hairs. Except for mature size which in R. lophanthae is about 2/3 the length of R. forestieri, the egg, larva, and pupa of both species closely resemble each other.
Adults of R. forestieri are about 1/8 inch (3 mm) long. Those of R. lophanthae are about 1/12 inch (2 mm) long. The Rhyzobius forestieri adult is all black, with black legs, and a thorax that on the underside is black. Rhyzobius lophanthae has black to dark reddish brown wing covers, a reddish brown head, legs, and thorax, and the underside of the abdomen and thorax are reddish brown to orangish.
The eggs are oval, pale yellow to whitish, and about 1/36 inch (0.7 mm) long in R. forestieri and somewhat shorter in R. lophanthae. Eggs commonly occur under a scale body, glued to a scale, or in protected places on a scale-infested plant.
The larvae are dark brownish to black on top and more pale underneath and covered with numerous short hairs. At maturity the larva of R. forestieri is about 1/5 inch (5 mm) long and that of R. lophanthae about 1/7 inch (3.5 mm) long. Young larvae commonly occur hidden feeding under the body or cover of an adult female scale.
The oval black or dark gray pupae are distinctly segmented and about the size of adults. Their rear end is glued to plant surfaces and the front end is somewhat raised from the surface. Fine white wax and the shriveled skin of the last instar occur at the base of the pupa.
Life Cycle
Lady beetles develop through 4 life stages: egg, larva, pupa, and adult. Adult females each lay about 200 to 400 eggs during their lifetime. The hatching larvae develop through 4 increasingly larger instars before pupating openly on the scale-infested plant.
The young larvae prefer to feed on scale eggs and crawlers. Adults and older larvae feed openly on all scale life stages.
Each adult female R. lophanthae consumes about 100 soft scale nymphs or 200 soft scale eggs during her lifetime and about twice that number or more if feeding on armored scales. Female R. forestieri consume about 150 soft scale nymphs or 300 soft scale eggs or about twice that number or more if feeding on armored scales.
The adult females live about 2 months. Development time from an egg to a reproductive adult is about 1 month when temperatures are warm. There appear to be about 3 generations per year in California. Overwintering is as adults in protected places.
Habitat
Rhyzobius forestieri and R. lophanthae, were deliberately introduced into California from Australia in the 1890s to control black scale. They then were named Rhyzobius ventralis and Lindorus lophanthae, respectively. However, R. ventralis, which is native to Australia is not known to occur in California. These lady beetles prefer to feed on various scale insects including those in the families Coccidae, Diaspididae, and Eriococcidae.
To improve biological control
- Control ants because they attack lady beetles and other natural enemies.
- Grow flowering insectary plants to provide nectar and pollen to feed adult natural enemies.
- Reduce dustiness that disrupts the activities of natural enemies (e.g., periodically hose off small plants).
- Avoid the application of broad-spectrum, persistent insecticides for all pests because they are toxic to natural enemies.
See Protecting Natural Enemies and Pollinators for more information.
Species
At least 191 species of lady beetles occur in California. Rhyzobius forestieri and R. lophanthae occur at least from Mendocino County to the southern border of California. Rhyzobius lophanthae is commonly called the black lady beetle. In the past their genus has been spelled Rhizobius.
More Information
- The Black Scale, UC Berkeley, California Agricultural Experiment Station Bulletin
- The Coccinellidae (Coleoptera) of America North of Mexico, Journal of the New York Entomological Society
- Forestier's Ladybird - Rhyzobius forestieri, New Zealand Factsheets
- Rhyzobius forestieri (Mulsant, 1853) (Coccinellidae), an Australian Ladybird New to Britain, from the Wildlife Garden of the Natural History Museum, London, The Coleopterist
- Rhyzobius ventralis (Erichson) and R. forestieri (Mulsant) (Coleoptera: Coccinellidae), Their Biology and Value for Scale Insect Control, Bulletin of Entomological Research
- Scale Morphology Effects on Feeding Behavior and Biological Control Potential of Rhyzobius lophanthae (Coleoptera: Coccinellidae), UC Riverside, Annals of the Entomological Society of America
Scientific classification:
- Phylum: Arthropoda
- Class: Insecta
- Order: Coleoptera
- Family: Coccinellidae
