The Carnation Fly, Hylemyia brunnescens (Zett.), which attacks cultivated species of Dianthus, has been studied in detail because the account given by Bruneteau (1930) was incomplete and that given by Séguy (1932) of two flies (H. brunnescens and H. cardui (Mg.)) on carnations was also incomplete and the identities of the stages studied were not fully established. For the first time, the development of H. brunnescens from egg to adult has been completed under observation and bred adults have been maintained in captivity until eggs were laid. The eggs, larvae and adults are described.

Eggs were laid in autumn. Oviposition began in the field on 7th September 1954 and on 12th September 1955 and eggs were present until early November. The behaviour of flies in captivity confirmed that eggs were laid only in autumn.

The larvae mined in the leaves and shoots. Early larvae finished feeding in November and entered the soil. Late larvae remained on the plants and fed intermittently through January and February, whenever the temperature was suitable. Mature and immature larvae on the plants survived exposure to severe frosts. Hibernation took place in the larval stage in the soil or in the feeding sites. Pupation occurred from mid-March to mid-April and the pupal stage lasted about eight weeks.

The emergence period for 122 flies was 4th–20th June 1955 with a peak period from 6th–12th June; other observed emergence periods were 30th May–4th June (1950), 2nd–9th June (1953) and 16th–26th May (1954). Captive flies lived from two to four months. They were active during the summer but they did not reach sexual maturity and begin to lay eggs until late August. There is thus only one generation a year and the slow development to sexual maturity ensures that the larval period occurs in autumn when the foliage of the host-plants is freshest and most abundant.