Phorbia

Robineau-Desvoidy, 1830

Wheat bulb fly, Black fly, Onion fly

Phorbia is a of in the . Several are significant agricultural pests, including Phorbia coarctata () on cereals, Phorbia securis () on wheat, and Phorbia cepetorum (Imported Onion ) on Allium . Some species engage in unusual mutualistic interactions with Epichloe , transporting spermatia between fungal individuals in a manner analogous to of angiosperms. The genus occurs in Europe and North America.

Pronunciation

How to pronounce Phorbia: //ˈfɔːr.bi.ə//

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Habitat

Agricultural fields, particularly cereal and onion . Phorbia coarctata prefers potato, swede, and sugar beet fields for . Phorbia securis infests cereal crops in semi-arid zones. Some associate with Epichloe-infected grasses.

Distribution

Europe and Northern America. Documented in Denmark, Norway, and Sweden. Phorbia securis occurs in Morocco (Chaouia, Doukkala, and Abda regions).

Seasonality

Phorbia coarctata: laying begins late June, peaks in July, ends in August. Main activity occurs in afternoon and evening until nightfall. Phorbia securis: two per year; first generation infests wheat from , second generation infests young tillering wheat at end of February and beginning of March.

Diet

feed on roots and stems. Phorbia coarctata larvae feed on wheat and other cereals. Phorbia cepetorum larvae feed on onion plants (Allium cepa). Phorbia securis larvae attack cereal stems, with highest damage to stems 14–20 cm long.

Host Associations

Triticum (wheat) - larval food sourcePhorbia coarctata and Phorbia securis
Allium cepa (onion) - larval food sourcePhorbia cepetorum
Solanum tuberosum (potato) - sitePhorbia coarctata
Brassica napus (swede, rapeseed) - sitePhorbia coarctata
Beta vulgaris (sugar beet, fodder beet) - sitePhorbia coarctata
Epichloe (fungus) - mutualistic spore transport spermatia between fungal individuals; interaction ranges from mutualistic to parasitic

Life Cycle

with , , , and stages. Phorbia securis has two per year. Phorbia coarctata eggs are laid on soil; larvae migrate to roots. occurs in soil.

Behavior

females preferentially oviposit on rough soil surfaces and in closed stands rather than open areas. Phorbia coarctata females more on dry soil than moist soil, and egg laying increases with declining light intensity. Artificial soil elevations attract more eggs on north-facing sides. exhibit specific behaviors ensuring cross- of Epichloe , analogous to in angiosperms. Males and females show differential attraction to traps, with females more strongly attracted.

Ecological Role

Agricultural pest causing serious damage to cereal and onion . for Epichloe fungal , providing ecological service analogous to . Some act as pollinating seed in convergent evolutionary system with .

Human Relevance

Several are economically significant pests requiring and control. Phorbia coarctata and Phorbia securis damage wheat and cereals; Phorbia cepetorum damages onions. Control methods include poisoned sprays. Phorbia securis reached damaging levels in 20% of surveyed Moroccan cereal fields.

Similar Taxa

DeliaBoth in contain agricultural pests; includes onion (D. antiqua) and (D. radicum), which overlap with Phorbia in use and . Delia generally have more pronounced bristle patterns on the .
HylemyaAnother with similar general and agricultural . Hylemya often lack the distinct characteristics and abdominal coloration patterns seen in Phorbia.

More Details

Fungal mutualism

The interaction between Phorbia and Epichloe represents a remarkable case of with angiosperm systems. The fungus provides rewards to flies, shows color change in fruiting structures after cross-, and exhibits -specific obligate —traits parallel to those in coevolved - systems.

Oviposition ecology

Phorbia coarctata exhibits sophisticated selection: are laid mainly within rows of swede, sugar beet, and fodder beet, but this pattern does not occur in potato fields. Rough soil texture and artificial elevations significantly influence site selection, with implications for cultural control methods.