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SOME EXPERIMENTS ON THE BREEDING OF THE MANGOLD FLY 



(PEGOMYIA HYOSOYAMI, PANZ.) AND THE DOCK FLY 



(PEGOMYIA BICOLOR, WIED.). 



By Alfred E. Cameron, M.A., D.Sc. (Aberd.), M.Sc. (Vict.), 

 Lecturer in Agricultural Biology, University College, Cardiff. 



In a previous paper (Ann. Applied Biol, i, 1914, pp. 41-76) in which the author 

 dealt with the life-history of Pegomyia hyoscyami, Panz., it was shown that the food- 

 plants of this species belonged principally to the natural orders Chenopodiaceae and 

 Solanaceae. Various weeds have also been cited in this connection, namely, certain 

 kinds of thistle and the dandelion. Recently E. M. Vassiliev (see Rev. Appl. Ent. iii, 

 Ser. A., 1915, p, 608) has added to the record the following : — Siletie (catchfly), 

 Datura stramonium (thorn-apple) and Onopordon acanihium (Scotch thistle). Thus, 

 in addition to the two aforementioned, the orders Caryophyllaceae and Compositae 

 are fairly well represented. As the original paper of the Russian author is not 

 available, it cannot be definitely stated in how far his records are authentic. But as 

 he advises the removal of these weeds from the vicinity of beet plantations, one would 

 naturally infer that he has some reason for assuming that they may be attacked by 

 the mangold fly and presumably provide an ever-present source of infestation to the 

 cultivated crop. 



As we have already stated {he. cit. p. 69), all suppositious assertions regarding the 

 food-plants of an insect species must be accepted with reserve, unless conclusive 

 proof is forthcoming in support. Although there may be a bad attack of mangold 

 fly in any one locality, we cannot therefore infer that weed plants in close proximity 

 which show similar damage are being also attacked by the same species. There are 

 several kinds of leaf-mining flies, and it is useless to argue that because a mangold or 

 beet plant has its leaves blistered, a similar condition in the case of thistles or any other 

 weed has been caused by the same species of maggot. It is our conviction that this 

 jumping at conclusions has led to the error now widely accepted and presented in 

 Leaflet 5 of the Board of Agriculture and Fisheries, that the dock is also a host plant 

 of the mangold fly, whereas the insect that attacks the dock is really Pegomyia bicolor, 

 Wied. , an allied species. In some cases another species is found to mine in dock leaves, 

 namely, Pegomyia nigritarsis, Zett., which can be readily distinguished from P. bicolor 

 in both the larval and adult stages (loc. cit. p. 64). 



The whole question of the food-plants of the mangold and dock flies requires 

 thorough revision, and experiments were undertaken at Holmes Chapel, Cheshire, 

 with this end in view. It was found that only a few of the questions could be dealt 

 with in one season, and it was hoped that the w^ork might be continued in the following 

 and subsequent summers. Thus, although finality has been by no means attained, 

 we consider it important that the results should be published. 



A previous attempt was made on a small scale to ascertain whether adults of 

 P. hyoscyami, reared from larvae which had fed on belladonna leaves, would oviposit 

 on the leaves of mangold wurzel (loc. cit. p. 69). The results were entirely negative, 



