THE CARROT RUST FLY 



By W. D. Whitcomb, 

 Research Professor of Entomology 



INTRODUCTION 



The carrot rust fly, Psila rosae Fab., is the most injurious member of the 

 dipterous family Psilidae, called the rust fly family by some authors. 



Although the yellowish hairs on the body of adults impart a somewhat rusty 

 appearance to the fly, it is apparent that the rusty color which appears on the 

 flesh and skin of carrots and parsnips after feeding by the larva is more respon- 

 sible for the name. These rusty scars are not characteristic of rust fly injury only, 

 but may be produced by any kind of injury to the skin of carrots and parsnips. 

 Similar rusty scars can be made on carrots by pricking the skin with the point 

 of a knife and scratching the surface with the fingernail. Many of the habits of 

 this fly — such as the laying of eggs on the soil and crown of the plant, feeding 

 on the roots by the larva, and pupation in the soil near by — are very similar 

 to the habits of the cabbage maggot, the onion maggot, and the seed corn maggot; 

 and it is suggested that, from the standpoint of both the economic entomologist 

 and the vegetable grower, a very appropriate and practical common name would 

 be the carrot maggot. 



HISTORY AND DISTRIBUTION 



The carrot rust fly was originally described in 1794 by Fabricius (7) as Musca 

 rosae and in 1805 (8) this was changed to Tephritis rosac. About 1835 it was 

 placed in both the genus Psilomyia and the genus Scatophaga by other authors, 

 but since 1880 it has been universally known as Psila rosae Fab. 



The original habitat of Psila rosae, according to Fabricius, was Kilia in Bes- 

 sarabia, which was formerly a province in southwestern Russia but is now con- 

 trolled by Rumania. In 1889 the habits of this insect and its injury to carrots were 

 described by Ormerod (22) in England, and at that time it had become a well- 

 known pest of carrots and parsnips in Germany and the British Isles. 



No attempt has been made to trace the history of P. rosae in Asia, Africa, or 

 South America, but in 1931 an infestation at Auckland, New Zealand, was re- 

 ported by J. Muggeridge (21), and the history of this insect in North America 

 indicates that it is likely to be present in any part of the world where climatic 

 conditions are suitable. Like many other root maggots, it thrives In cool, damp 

 locations, and it is interesting to note that it has never been reported south of 

 40° latitude in North America. 



Information on the distribution of this insect in North America has been 

 secured through the courtesy of the entomologists in the various States and 

 Provinces, and the Insect Pest Survey of the Bureau of Entomology and Plant 

 Quarantine, United States Department of Agriculture. 



CANADA 



Psila rosae Fab. was first reported in North America in 1885 by Dr. James 

 Fletcher, Dominion Entomologist of Canada (10) who identified specimens reared 

 from carrots purchased in the market at Ottawa. Much injury occurred in the 

 vicinity of Montreal, Quebec, and Ottawa in 1886 (11), but this pest apparently 

 did not cause serious losses again until 1895-99 when another outbreak occurred 



