Occurrence of Adults of the Carrot Rust Fly, Psila rosae (Fab.) (Diptera: Psilidae), on Corn Foliage at Bradford, Ontario

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Abstract
Adults of the carrot rust fly, Psila rosae (Fab.), are difficult to find in the field. Frequently they can be found in light to moderate numbers in some situations, occasionally in large numbers, rarely in moderate to large numbers over a period of several days. Fabricius (1794, p. 356) reported that they were found commonly on flowers in Kiel, Germany. Curtis (1860, p. 405) wrote, “The fly…was named rosae by Fabricius, being found probably sunning itself upon the leaves of rose bushes”. Several British writers observed that the flies were most numerous in the parts of carrot fields sheltered by hedges. Baker et al. (1942) wrote: “Flies were present in small numbers on certain weeds, but in considerable numbers in the hawthorn hedges”. Roebuck (1945), Wilson (1945), Petherbridge et al. (1945), and Wright et al. (1945) made similar observations. Some British writers reported flies on various plants, as follows: Whitehead (1890), on low shrubs near streams and in meadows; Smith (1921), on sallow, oak, and hazel; Petherbridge et al. (1942, 1943, 1945), on wild chervil (Anthriscus sylvestris) , hemlock (Conium maculatum), nettles, and potatoes; Wilson (1945), on coarse herbage, growing crops (especially potato), weeds (especially nettles); and Wright et al. (1946), on trees, hedges, and ditches with a thick herb covering.