February, ’24] 
PETERSON: CHEMOTROPISM OF HYLEMYIA 
91 
fields. This may be due to the fact that the flies in wet fields readily 
secure sufficient moisture to satisfy their thirst, consequently wet 
baits are not so attractive in wet fields as in dry fields. 
At the outset a number of traps were run to determine the attractive¬ 
ness of water diluted solutions of brown sugar, molasses, honey, corn 
syrup, cane sugar, maltose, lactose and dextrose. The first three prod¬ 
ucts attracted a moderate number of flies while the last five substances 
attracted few or no flies. Honey, as a rule, was the most attractive. 
In connection with the tests on the attractiveness of the media, ad¬ 
ditional traps were run with the respective media where parts of young 
onion plants were added. In most cases slices of the bulb portion 
was used while in a few tests pieces of green onion tops (leaves) were 
employed. There was little or no difference in the attractiveness of the 
onion bulb or onion tops. In a few cases the baits containing pieces of 
onion tops attracted a few more flies than the baits containing slices of 
the bulb portion. As a rule the addition of pieces of growing onions to 
most of the media increased the attractiveness of the bait about twice 
for both species. In a few cases 3 to 5 times as many flies were caught 
in the traps where parts of an onion were added as in the checks (media 
and water alone). 
An examination of the list of substances tried shows a number of 
essential oils and closely related products. All of these were given at 
least three trials using corn syrup and other media. The majority had 
little or no attraction for the flies of either species. Oil of nutmeg, oil of 
peach kernels, clove oil, true mustard oil and fusel oil gave some indi¬ 
cation of being attractive in some of the trials. They were primarily 
attractive to Hylemyia cilicrura Rond. In the majority of the tests 
these oils attracted 4 to 6 times as many flies as the check trap (medium 
plus water). 
In conjunction with the study of essential oils several allyl products 
were tried; allyl sulfide, allyl iodide, allyl bromide and allyl alcohol. 
The chief reason for giving these products a test was due to the fact that 
it has been shown by several investigators that the odor of the onion 
is an allyl product, probably closely associated with allyl sulfide. In 
quite a large series of field tests with the allyl products named in different 
media and under varying outdoor conditions allyl alcohol was the only 
allyl product which was attractive. This substance in most cases was 
highly attractive to both species of flies. In numerous instances the 
presence of allyl alcohol attracted, 5,10 and in some cases 15 or more 
times as many flies as the media by itself. Some media with allyl 
