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JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 8 



issuing from July 1-12. We determined by a series of daily dis- 

 sections of twenty flies which were captured by sweeping the onions 

 with an insect-net, when the second brood is about to oviposit in the 

 onion fields. On July 10, 55 per cent of the females dissected contained 

 almost fully-developed eggs in the ovaries. Two of the twenty speci- 

 mens dissected on this date had already deposited eggs, for only two 

 ripe eggs were found in the ovaries of one female and three were pres- 

 ent in the other. 



Ill Natural Enemies 



The most important natural enemy of the onion maggot in Wiscon- 

 sin is a Staphylinid or rove beetle (Aleochara anthomyice Sprague). 

 On July 1, three hundred imported onion fly puparia were sieved from 

 the soil in a green onion bed. From July 16-30, twenty-seven (9 per 

 cent) Staphylinids emerged, whereas the last onion fly issued on 

 July 13, from these puparia. When an onion maggot is dropped into 

 the breeding jar near the Staphylinids, the larva is seized by the 

 mandibles of the beetles and the Coleoptera tenaciously cling to the 

 wriggling maggot as the victim is being devoured. In the field masses 

 of onion fly. eggs were found which had been partly devoured by some 

 predaceous enemy, and it may be possible that the Staphylinids preyed 

 upon these eggs. 



Two wasps (Oxyhelus Jf-notatus Say), each dragging an onion fly, were 

 captured in an onion field, on July 21. In all probability, this wasp 

 sometimes provisions its nest with this pest. 



Spiders were frequently observed sucking out the juices of the 

 imported onion flies. These spiders were commonly seen lying in wait 

 for their prey at the union of two onion leaves. 



A single Hymenopterous parasite was bred from an imported onion 

 fly puparium on August 31. On June 25, the parasitized onion fly 

 larva pupated under laboratory conditions. Mr. J. C. Crawford, U. S. 

 National Museum, identifled this parasite as, " Cothonaspis n. subg." 

 This is due, he states, "to its having only 11 joints in the antennae 

 instead of 12 or 13 as the various subgenera of Cothonaspis have. 

 However, there is only one specimen, and he is loath to describe it as a 

 new subgenus since occasionally these vary and this might be a speci- 

 men with abnormal antennae." A number of specimens of another 

 Hymenopterous parasite were bred from puparia obtained from 

 larvae which completed their development in radishes. This parasite 

 was placed in the genus Cothonaspis by the same speciahst. Mr. 

 F. Knab, U. S. Bureau of Entomology, identified two species of Antho- 

 myids which were bred from radishes, the seed-corn maggot {Phorbia 

 fusciceps Zett.) and the cabbage maggot {Phorbia brassicce Bouche). 



