Pest profile

Mildew-Eating Lady Beetles

Psyllobora species (mainly P. vigintimaculata) · Coleoptera: Coccinellidae[2]

Unlike most lady beetles, Psyllobora species won't eat insects. They feed on powdery mildew, so finding them means the fungus is present.[1]

Twentyspotted lady beetle, a small cream-colored lady beetle with dark spots, on a green leaf
Twentyspotted lady beetle, a small cream-colored lady beetle with dark spots, on a green leaf. (c) Will Linnard, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0

How to identify it

  • Psyllobora vigintimaculata adults are 1/8 to 1/6 inch long, round and domed.[1]
  • The thorax and wing covers are cream, pale gray or yellowish with four or five spots on the thorax and usually eight or nine on each wing cover.[1]
  • In many individuals the spots run together, and some have orange marks.[1]
  • Larvae are pale gray to whitish with dark markings that get bolder as they grow.[1]

Where it lives

P. vigintimaculata ranges through the contiguous United States, western Canada and Alaska and on into Central and northern South America.[1]

US map: public records from 45 states since 1990 (GBIF).

Biology and life cycle

Females lay small egg groups mostly under leaves where powdery mildew grows.[1]

Egg to reproductive adult takes three to four weeks, with multiple generations a year.[1]

In California, adults can be active from at least February to mid-December.[1]

Damage and signs

  • They eat the threads, spores and spore structures of powdery mildews and must have them to survive and reproduce.[1]
  • During its growth, one larva clears the mildew from about one square inch of leaf.[1]

Health risk

They feed only on powdery mildew, and UC IPM describes no risk to people.[1]

Control

Prevention

Treat the beetles as a sign of powdery mildew, not as a pest; their numbers rise as mildew spreads.[1]

Biological control

Flowering plants, ant control and avoiding persistent, broad-spectrum insecticides help keep these beetles around.[1]

Common questions

Why are lady beetles on my mildewed squash?
They may be Psyllobora, which eat powdery mildew and become more common as mildew increases.[1]
Will they eat my aphids?
No. Psyllobora species won't feed on insects.[1]
Are the whitish spotted larvae a pest?
No. They're Psyllobora larvae grazing on powdery mildew.[1]

Sources

  1. University of California Statewide IPM Program, “Fungus-Feeding Psyllobora Lady Beetles (Natural Enemies Gallery).” ipm.ucanr.edu/natural-enemies/fungus-feeding-psyllobora-lady-beetles/ (accessed 2026-10-06)
  2. iNaturalist, “Psyllobora vigintimaculata taxon page (order and family).” www.inaturalist.org/taxa/118967 (accessed 2026-10-06)

Updated 2026-10-14. Built from sourced records. Spot an error? Tell us.