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Smith (K. M.). The Bionomics of the Carrot Fly {Psila rosae, Fab.). 

 Some Further Methods of Control. — Fniit-Groner, Fruiterer, 

 Florist & Mkt. Gdnr., London, Hi, no. 1359, 15th December 1921, 

 pp. 955-958, and no. 1360, 22nd December 1921, pp. 993-994, 

 18 figs. 



Some account of Psila rosae, F. (carrot fly) and the injuries it causes 

 has been given in a preUminar}^ paper [R. A.E., A, x, 49]. The eggs 

 are exceedingly small and difficult to find, being hidden in the soil 

 close to the plant, sometimes singly, sometimes in clusters. A female 

 dissected 16 da3's after emergence was found to contain 97 ripe eggs 

 and many unripe ones. The incubation period is about 12-19 

 days. The young larva bores its way into the carrot, and generallj- 

 feeds with the posterior end of the body protuding from the root. 

 The larval period is very variable, depending largely on weather 

 conditions ; normally it lasts about four weeks, but this ma\' be 

 prolonged to six or seven weeks in cold weather. When carrots 

 are stored in a warm place, the larvae will continue to feed and develop 

 throughout the winter months. Pupae are found in the soil close to 

 the carrot, sometimes adhering to it. The pupal period varies even 

 more than the larv^al, sometimes lasting about a month and sometimes 

 continuing throughout the \dnter. The adult fly is described. Similar 

 species, which are frequently confused with P. rosae, are P.nigricornis 

 and P. iiniseta ; the characters differentiating these species are described. 



Male flies under observation began to die after 14-17 days ; females 

 lived from 38 to 45 days. If given an unlimited supply of sugar and 

 water, the flies would feed until the abdomen burst ; this might be 

 used as a remedial measure in the same manner as the poison bait 

 used against the onion fly, Hylemyia antiqiia. There are two genera- 

 tions of P. rosae in a season, but neither is complete, as many pupae 

 of the first generation overwinter. Larvae of the second generation 

 pupate about the end of September and emerge in the following spring. 

 The seasonal incidence varies considerably ; a table records the obser- 

 vations in the field in 1920. While hibernation usually occurs in the 

 pupal stage, there is reason to beUeve that the adults of the second 

 generation may also hibernate. 



The question of wild food-plants of P. rosae is an important one ; 

 numbers of them have been found on UmbelHferous plants, and in 

 May many were taken on cow parsley { Anthriscus sylvestris) before 

 carrots were above ground. It is not yet known what happens to 

 the flies emerging early in May from overwintering pupae, or on what 

 they or their larvae feed between that date and the first appearance 

 of the carrots. It is possible that they subsist on Umbelliferous weeds. 

 On the other hand, the closely allied species, P. nigricornis and 

 P. uniseta, and also P. rosae, have been found upon sallow, oak and 

 hazel in woods, etc., though they may have been only sheltering 

 on these. 



Three Braconid parasites have been bred from pupae of P. rosae. 

 One of these has been identified as Aphaereta cephalotes, the others 

 are two new species of Dacmtsa. Experiments fn^cdntrol, on the lines 

 indicated in the earlier paper Hoc. cit.] were planned for the season 

 of 1921. The trials are outhned, but unfortunately no results could 

 be obtained, owing to the entire absence of P. rosae in the locahties 

 chosen for the experiments. 



(5733) Wt. P.3 184 1,500 3/22 Harrow G.75,3 H 



