Hosts or Prey
Powdery mildews
Identification
Of the several Psyllobora species in California P. vigintimaculata is apparently the most common. Psyllobora vigintimaculata adults (also called ladybugs or ladybird beetles) are round when viewed from above, dome shaped (convex) when viewed from the side, and 1/8 to 1/6 inch (3–4 mm) long. The wing covers and thorax are cream-colored, pale grayish, or yellowish with 4 or 5 blackish to brown spots on the thorax and commonly 8 or 9 black to brown spots on each wing cover. However, in many individuals some to nearly all of the spots merge together. Some adults also have orangish markings on the wing covers.
Eggs are football shaped and laid on end in a group. They are whitish and about 1/32 inch (0.8 mm) long.
Larvae are pale gray to whitish with blackish to dark gray markings that are more prominent in later instars. First instars (larvae) are about 1/32 inch (0.8 mm) long. The last (fourth) instars are about 1/7 inch (3.5 mm) long.
Pupae are about 1/12 inch (2 mm) long. They are initially white but become gray with black spots as they age.
Life Cycle
Lady beetles develop through four life stages: egg, larva, pupa, and adult. Adult females lay eggs in a group of a few mostly on the underside of leaves where powdery mildew is growing. The hatching larvae develop through four increasingly larger instars. Pupae occur openly glued to plant parts.
Unlike most lady beetles, Psyllobora species will not feed on insects. Psyllobora vigintimaculata must consume the mycelia, spores, and spore-forming structures of powdery mildews to reproduce and survive. For example, during its development a larva consumes all the powdery mildew covering about 1 square inch of leaf surface. The beetle's abundance increases with an increasing prevalence of powdery mildew.
Psyllobora vigintimaculata adults can be active in California from at least February through mid-December. Egg to reproductive adult development time is 3 or 4 weeks when temperatures average 77 and 68ºF, respectively. Psyllobora species have multiple generations per year.
Habitat
Psyllobora vigintimaculata can occur on almost any plant on which a powdery mildew is growing. Its habitats include field and tree crops, gardens, landscapes, and wildlands. To improve biological control
- Control ants because they attack natural enemies of lady beetles and various other pests.
- 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. These include at least 4 Psyllobora species: P. borealis, P. meticulosa, P. renifer, and P. vigintimaculata. Psyllobora vigintimaculata occurs throughout the contiguous United States through Western Canada and into Alaska and in Central America and northern South America. Psyllobora vigintimaculata is sometimes called the small ashy gray lady beetle or twenty-spotted lady beetle.
More Information
- Biology and Co-Occurrence of Psyllobora vigintimaculata taedata (Coleoptera: Coccinellidae) and Powdery Mildews, UC Davis, Annals of the Entomological Society of America
- The Coccinellidae (Coleoptera) of America North of Mexico, Journal of the New York Entomological Society
- The Feasibility of Using Psyllobora vigintimaculata (Coleoptera: Coccinellidae), a Mycophagous Ladybird Beetle, for Management of Powdery Mildew Fungi (Erysiphales) (PDF), Ph.D. Dissertation, UC Davis
- Twenty-Spotted Ladybird Beetle, UC Irvine
Scientific classification:
- Phylum: Arthropoda
- Class: Insecta
- Order: Coleoptera
- Family: Coccinellidae
