Pieris oleracea

(Harris, 1829)

Mustard White

Pieris oleracea, the mustard , is a in the to Canada and the northeastern United States. The exhibits two distinct seasonal forms: spring individuals display prominent green or on the undersides visible even from above, while summer individuals appear nearly all-white with fainter markings. are currently declining due to the spread of garlic mustard (Alliaria petiolata), which is toxic to despite attracting ovipositing females. The species is biovoltine in most of its range, with two annually, though southern Ontario populations may produce three to four and northern populations sometimes only one.

Pieris oleracea by (c) Steven Joyner, some rights reserved (CC BY), uploaded by Steven Joyner. Used under a CC-BY license.

Pieris oleracea by the Smithsonian. Used under a CC0 license.

Pronunciation

How to pronounce Pieris oleracea: //ˈpaɪərɪs ˌɒləˈræsiə//

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

Identification

Distinguished from similar Pieris by the green or on the underside of the . In spring, this green coloration is dark and visible from the surface; in summer it becomes faint. This seasonal is unique among North Pieris. Distinguished from P. rapae (cabbage ) by the green venation (P. rapae has gray or yellow underside without green veining) and smaller black spots. Distinguished from P. virginiensis (West Virginia white) and P. marginalis (margined white) by pattern and geographic distribution.

Images

Habitat

Found in prairies, near streams, and in moist deciduous woodlands. In spring, occurs more frequently in moist woodlands or open fields. Occupies where Brassicaceae plants occur.

Distribution

to Canada and the northeastern United States. Range extends from Newfoundland west to Alberta and the Northwest Territories in Canada, including north and central British Columbia, the Cypress Hills of Saskatchewan, and coastal Nunavut at Coppermine and Arviat. In the United States, occurs in New England states and the Great Lakes region. are expanding northward in response to climate change.

Seasonality

Biovoltine in most of range, with periods typically in June and late July. In southern Ontario, three to four may occur. In northern parts of range, only one generation has been observed. Spring form appears earlier in the season; summer form appears later.

Diet

feed on Brassicaceae, primarily Cardamine (bittercress) and Boechera (rockcress) . feed on nectar from plants and other available flowers.

Host Associations

Cardamine - larval bittercress
Boechera - larval rockcress
Alliaria petiolata - toxic associationgarlic mustard; attracts ovipositing females but toxic to

Life Cycle

with . laid on plants. through multiple , with mature larvae showing green coloration with black spots and dark stripe. occurs on host plants or nearby vegetation. Two per year in most of range; variable from one to four generations depending on latitude and local conditions.

Behavior

Males during daylight hours to locate females for mating. Females exhibit strong response to sinigrin, a glucosinolate found in plants. This chemical cue also attracts females to the Alliaria petiolata, despite its to offspring. Limited evidence suggests potential evolutionary to garlic mustard in with long-term exposure, though this appears slow.

Ecological Role

specializing on Brassicaceae. Serves as for and other . Functions as when feeding on nectar. declines may indicate disruption from and modification.

Human Relevance

declines have generated concern. The illustrates ecological impacts of , as garlic mustard threatens survival through a combination of chemical and of . Research on this system informs understanding of evolutionary to novel hosts and invasive species management.

Similar Taxa

Pieris rapaeSimilar size and general appearance, but P. rapae has gray or underside without green , larger black spots, and is an that has competitively displaced P. oleracea in some New England areas.
Pieris virginiensisSimilar appearance and preferences, but P. virginiensis is with more restricted range; distinguished by pattern details and .
Pieris marginalisSimilar appearance and geographic overlap; distinguished by pattern and seasonal form differences.
Pieris napiGreen-veined ; similar green on underside but distinguished by geographic distribution (primarily European and western North ) and pattern details.

More Details

Invasive species threat

Alliaria petiolata (garlic mustard) produces sinigrin, an stimulant that attracts P. oleracea females. However, the contains alliarinoside and cyanide compounds toxic to . This 'evolutionary trap' causes females to lay on unsuitable . Garlic mustard's formation of dense displaces Cardamine and Boechera hosts, compounding declines.

Potential adaptation

Short-term studies suggest with long-term garlic mustard exposure show slightly improved larval survival on this compared to naive populations, indicating possible incipient . However, estimated adaptation time of approximately 100 , combined with rapid garlic mustard spread and small population sizes, makes passive adaptation an unlikely solution.

Climate change response

Documented northward range expansion associated with warming climate. Southern Ontario show increased (3-4 ) compared to historical patterns.