Obolodiplosis robiniae

(Haldeman, 1847)

locust gall midge, black locust gall midge

Obolodiplosis robiniae is a small gall midge (Diptera: Cecidomyiidae) native to eastern North America that has become a significant pest in Eurasia. The is monophagous on Robinia species, particularly black locust (Robinia pseudoacacia), forming distinctive leaf margin roll galls through gregarious larval feeding. First described from Pennsylvania in 1847, it was detected in Asia in 2002-2003 (Japan, Korea) and Europe in 2003 (Italy), subsequently spreading explosively to 26 European countries and much of China. Climate modeling predicts substantial northward range expansion under warming scenarios, with suitable potentially increasing by 35% by 2070. The reduces tree growth and productivity, causes early leaf abscission, and facilitates secondary pest attacks by wood-boring beetles.

Obolodiplosis robiniae by (c) Stephen Thorpe, some rights reserved (CC BY), uploaded by Stephen Thorpe. Used under a CC-BY license.Obolodiplosis robiniae by (c) Alexis Tinker-Tsavalas, some rights reserved (CC BY), uploaded by Alexis Tinker-Tsavalas. Used under a CC-BY license.Obolodiplosis robiniae by no rights reserved, uploaded by Stephen James McWilliam. Used under a CC0 license.

Pronunciation

How to pronounce Obolodiplosis robiniae: //ˌoʊbəloʊdɪˈploʊsɪs rɒˈbɪni.aɪ//

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

Identification

are minute flies typical of gall midges. Larvae cause diagnostic leaf margin roll galls on Robinia leaflets—thickened, downward-curved margins that enclose gregarious larvae. Galls appear as curled or rolled edges along leaflet margins, often with 1-6 galls per leaflet. Mature galls may show color changes from green to reddish as photosynthetic pigments degrade. The is distinguished from other Robinia-feeding gall midges by the specific gall and marginal location. Seasonal timing aids identification: adults emerge in spring, with 2-4 per year in invaded regions.

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Habitat

Urban and suburban areas where ornamental or weedy black locust trees occur; forest edges and disturbed with Robinia presence. Native range in eastern North American deciduous forests. range spans temperate Eurasia from 21°-66°N, primarily in semi-humid to semi-arid regions where black locust grows vigorously. Climate envelope modeling indicates strong temperature dependence, with optimal conditions in areas matching black locust's fastest growth rates.

Distribution

Native to North America: eastern United States (Pennsylvania, New York) and southeastern Canada (Ontario, Quebec, New Brunswick, Nova Scotia, Prince Edward Island, British Columbia). in Eurasia: discovered 2002-2003 in Japan, Korea, and Italy; by 2007 spread to 26 European countries including Austria, Germany, France, UK, Sweden, Ukraine; in China detected 2004 in Hebei, now in 17 provinces. Rapid eastward expansion from Italy to Ukraine (2000 km, 2003-2006). Predicted to continue northward expansion with climate warming.

Seasonality

emerge in spring following as diapausing larvae. In temperate Europe, completes 2-4 annually depending on conditions: two generations on mature trees ( declining in summer), two additional generations possible on root suckers from midsummer onward. Peak population densities occur in late spring. In Korea, seasonal distribution studies show fluctuation within tree crowns throughout growing season.

Diet

Monophagous; larvae feed exclusively on Robinia . Gregarious feeding on leaf parenchyma induces gall formation. Nutritive tissue within galls rich in starch and octadecanoic acid (C18:0), which serves as primary larval food source. plants include black locust (Robinia pseudoacacia), bristly locust (R. hispida), and clammy locust (R. viscosa).

Host Associations

  • Robinia pseudoacacia - primary black locust, main throughout range
  • Robinia hispida - bristly locust
  • Robinia viscosa - clamy locust
  • Robinia pseudoacacia 'Aurea' - golden-leaved cultivar

Life Cycle

Overwinters as diapausing larva within gall or soil. emerge in spring. Females deposit on developing leaflets. Larvae are endophytic, feeding gregariously within leaf margin galls. occurs within gall or in soil. time varies: 2-4 generations per year possible in optimal conditions. Multiple overlapping generations common in mid-to-late season on root suckers.

Behavior

Gregarious larval feeding induces characteristic leaf margin roll galls by thickening and bending leaflet margins downward. Up to 5-6 larvae may occupy a single gall. occur throughout the growing season from initial leaf development until leaf fall. High densities cause early leaf abscission and reduced . Facilitates secondary attack by longhorn beetles (Cerambycidae) and jewel beetles (Buprestidae) through tree stress or gall damage.

Ecological Role

pest with significant negative and economic impacts. Reduces growth and productivity of trees, diminishes ornamental value, and can cause tree mortality through secondary pest facilitation. In native range, likely maintained at lower densities by co-evolved natural enemies. In invaded range, subject to by introduced and native , particularly Platygaster robiniae (Platygastridae), which can achieve 40% rates. Potential value as biological control agent against weedy black locust in some contexts, though generally considered detrimental.

Human Relevance

Significant forestry and urban tree pest in Europe and Asia. Causes aesthetic damage to ornamental black locust, reduces timber productivity, and increases tree vulnerability to fatal secondary borer . Subject to and management efforts by forestry departments. Scientific model for studying insect spread, climate change impacts on pest distribution, and plant-gall former interactions. -level sequenced (2024).

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