Unaspis euonymi

(Comstock, 1881)

Euonymus Scale

Unaspis euonymi is a diaspidid insect native to East Asia and now widespread as an pest. It infests Euonymus and several other ornamental plants, causing significant damage in urban and suburban landscapes. The species exhibits pronounced in both and feeding . It has been extensively studied as a target for using introduced and native natural enemies.

Unaspis euonymi by (c) Paul Cook, some rights reserved (CC BY), uploaded by Paul Cook. Used under a CC-BY license.

Pronunciation

How to pronounce Unaspis euonymi: /juːˈnæspɪs juːoˈnaɪmi/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

females are dark brown to gray, oyster-shaped or pear-shaped, approximately 1.5–2 mm long, with a characteristic dark zygotic cover. Adult males are smaller, elongated, and white with a three-lobed end. Males retain legs and as adults; females are legless and . Second-instar nymphs are the stage and can be distinguished by their flattened, -like appearance on stems and leaves.

Images

Habitat

Urban and suburban landscapes, nurseries, and ornamental plantings. Found on plants in both "protected" environments (higher rates) and "unprotected" environments. Older plants and certain cultivars of Euonymus show higher infestation levels.

Distribution

Native to East Asia (China, Japan, Korea). Introduced and established in North America (USA, Canada, Mexico), Europe (Austria, Britain, Bulgaria, France, Greece, Hungary, Italy, Spain, Switzerland, and others), Mediterranean region, Middle East (Israel, Turkey, Iran), North Africa (Algeria, Morocco, Egypt), South America (Argentina, Bolivia), and Central Asia.

Seasonality

Overwinters as second-instar nymphs. males emerge and mature earlier than females, with males producing multiple per year while females produce one generation annually. Peak activity timing varies by region; in Virginia, USA, highest recovery rates occurred in late May.

Diet

Phloem-feeding on Euonymus , particularly Euonymus japonicus. Also recorded from Prunus, Hibiscus, and other ornamentals.

Host Associations

Euonymus japonicus - primary Main ; males feed primarily on leaves, females on stems
Euonymus japonica var. aureovariegata - More frequently infested than other tested cultivars
Prunus - Recorded from distribution sources
Hibiscus - Recorded from distribution sources

Life Cycle

with distinct male and female developmental schedules. Males have shorter development time and produce multiple annually. Females have longer development and produce one generation per year. Both sexes overwinter as second-instar nymphs. Differential timing reduces between sexes.

Behavior

in feeding site selection: males feed primarily on leaves (75% upper surface, 25% lower surface), while adult females feed almost exclusively on stems (94% stems, 6% leaves). This spatial partitioning reduces . Males are mobile as adults; females remain .

Ecological Role

Pest of ornamental plants. Serves as for specialized (Encarsia citrina, Aspidiotiphagus spp., Encarsia spp.) and (Chilocorus kuwanae, Cybocephalus nipponicus) that have been introduced for . Subject of extensive biological control research and implementation.

Human Relevance

Significant economic pest of Euonymus and other ornamental shrubs in landscaping and nursery industries. Damage causes yellowing, defoliation, and plant death. Management relies on agents, , and . Older plants and certain cultivars are more susceptible.

Similar Taxa

Quadraspidiotus perniciosusSan Jose ; shares (Encarsia citrina) and is congeneric in Diaspididae, but differs in range and female scale cover
Other Unaspis species members share oyster-shaped female covers and similar ; identification requires examination of pygidial duct details and associations