February, ’IS] Howard: poisoned bait for onion maggot 
83 
By the first week in June the maggots were doing much damage to 
the young onions, and by the end of June the infestation was serious. 
Apparently no benefits whatever had accrued from the use of the poi¬ 
soned bait, and the application was discontinued. One field of three 
acres showed a 75 per cent infestation, others 50 per cent or less. 
During the next eight weeks a series of fly trap experiments were 
performed to ascertain the attractiveness of various baits, and to deter¬ 
mine the killing properties of the poison. In these experiments 14 
baits were used. Over 12,000 adults of the three species of root mag¬ 
gots prevalent in the locality were trapped, examined, and counted. 
The males were determined specifically, but the females were counted 
in toto. The total, 12,084, showed 59.4 per cent or 7,176 females, and 
40.6 per cent or 4,908 males, of the species Hylemyia antiqua, Phorbia 
brassicce, and Pegomyia fusciceps. 
Of the baits used, Sanders formula, with the addition of sliced onion, 
proved to be 300 per cent more attractive than the unmodified bait of 
dilute molasses. Fresh onion ranked second, while plain dilute molas¬ 
ses ranked third. Of the other baits, stale beer attracted a large num¬ 
ber of these flies as well as many others. 
To determine the toxicity of the baits, check traps were included in 
the above experiment. Comparison of the mortality of the flies in 
these traps with the mortality in traps containing the same bait with 
sodium arsenite added, showed that from 11 to 50 per cent mortality 
was traceable to the poison. The general average was very low, not 
over 15 per cent. This would indicate that large numbers of flies are 
attracted to the baits but do not feed. Of course most of the flies 
which visited the baits entered the traps, whether they fed or not. 
Collections of flies before and 2 hours after the application of the 
spray, on June 23, showed 20 per cent mortality due to spraying, 53 
hours later. 
Ten experiments were performed in the laboratory to determine if 
the sodium arsenite was effective at the rate used. From 12 to 56 flies 
were used in single experiments, and feeding was observed in almost 
every case. The general conclusions of all the experiments were that 
sodium arsenite at 5 grams to the gallon is fatal to the onion fly, the 
cabbage fly, and the fringed Anthomyian. The poison took visible 
effect in 5 to 8 hours, and was fatal in this length of time to 37 per cent 
(checks run in each experiment). It proved fatal in from 20 to 22 hours 
to 50 to 100 per cent of the flies. In several of the experiments, flies 
reared from onions were used. Plain molasses, which was usually fed 
the flies in the check, is a very suitable food. Adults have been kept 
living on this diet for as long as 36 days. 
