348 



JOURNAL OF ECONOMIC ENTOMOLOGY 



diluted molasses. After half an onion field was baited we were con- 

 vinced that thorough spraying was not necessary, as there was no ques- 

 tion of douht that the diluted molasses clearly attracted this pest. In the 

 sprayed portion of the onion field, numerous flies were seen on the 

 onion leaves feeding on the minute droplets of this insecticide until 

 their abdomens became greatly distended, but in the unsprayed part 

 of the onion field, rarely w^as an Anthomyid seen exposed to the sun- 

 shine on the tops of the onion leaves. The following formula was used 

 in this experiment: 



Molasses 1 pt. 



Sodium arsenite (dissolved in boiling water) J oz. 



Water 1 gal. 



Four applications of the spray were made to control the second 

 brood of onion flies in this somew^hat isolated onion field in which the 

 pest had already destroj^ed 50 per cent of the crop. The bait was 

 renewed once during each week. 



On account of the severe thrip injury to the onion leaves in this 

 field it was difficult to determine whether the waxy coating of the 

 leaves insured protection from the burning of the soluble poison. 



The results obtained were most encouraging in this somewhat isolated 

 onion field for few infested onions were found compared with the ravages 

 of the pest in some of the onion farms in the vicinity. As the season's 

 work was started too late to test the effectiveness of the poisoned bait 

 against the first brood of the pest, which is probably more difficult to 

 combat on account of the frequent spring rains which wash off the 

 spray, no conclusions can be drawn from the good shomng that the 

 spray made against the second brood. 



To control the imported onion fly in a commercial onion field which 

 is surrounded by other infested onion farms, may present a more 

 difficult problem on account of the invasion of the pest from adjacent 

 fields. It may be possible that if one grower sprays and his neighbors 

 do not, that a few applications of the bait to the entire onion field 

 followed by spraying of the margins adjacent to the unsprayed fields, 

 may control the invading flies. This work must be continued during a 

 number of seasons to determine whether the pest can be controlled in 

 non-isolated onion fields. 



VI Black Onion Fly {Tritoxa flexa Wied.) 



According to Chittenden^ the black onion fly {Tritoxa flexa Wied.) 

 is ''an old enemy of the onion and a native species, recorded from the 



^ Chittenden, F. H. Insects Injurious to Vegetables, p. 245. 



