RESULTS 
Under field conditions the syrup bait consisting of 1 pint of Karo syrup 
and 13 grams of Bayer L 13/59 dried and lost its tackiness in about 4 hours. 
It gradually hardened until it was tough and plastic. 
Flies were attracted to the bait as soon as it was applied and con- 
tinued to be attracted to it after it had hardened, even when it was covered 
with dust and dead flies. 
After locating the bait, flies showed no disposition to leave, but fed 
avidly, dissolving the hardened Karo with their salivary secretions. They 
showed distress symptoms in 1 to 3 minutes after beginning ingestion of the 
bait, and immobility or at least complete loss of co-ordination in 5 to 15 min- 
utes. No flies that fed sufficiently to exhibit distress symptoms were known 
to recover. 
Not only did the hardened bait continue to attract flies throughout the 
summer of 1953; it continued to kill them. Applications of hardened Karo 
containing Bayer L 13/59 were apparently as lethal to house flies in October 
as in June, when they were made. 
Fight ounces of bait applied as thin dribbles in about two dozen places 
on partitions and posts were sufficient to give 94 per cent control in a 20- by 
50-foot calf barn in which fly production was going on in the litter of stalls. 
Less than a quarter ounce applied in thin strips in about a dozen places along 
window ledges and partitions gave better than 93 per cent control in a store, 
20 by 40 feet, that sold dairy products and that was screened but that had 
many customers passing in and out each day; observations indicated that a 
larger amount of bait applied in a greater number of places would have given 
better contrcel. 
Generally, hardened bait gave the best house fly control on those pre- 
mises having a high level of sanitation and effective screening, table 2. In 
the Grade A dairy barns, which had a high standard of sanitation and fly 
exclusion by windows and screens, the hardened bait gave control that ranged 
between 90 and 95 per cent. In most dairy and feeder barns that were un- 
screened, the bait was ineffective because, although it killed many flies, 
other flies quickly moved in to replace most of those that had been destroyed. 
The sheep barn, in which 92.5 per cent control was obtained, was isolated 
from other sources of infestation and had few or no fly-breeding areas on or 
near the premises. In the baited south part of an H-shaped calf barn, not 
listed in table 2, the house fly population was noticeably reduced but not 
adequately controlled, figs. 4 and 5, because flies moved in from the unbaited 
north part of the barn and from outdoors. 
The reason for the unexpectedly strong residual properties of 
Bayer L 13/59 when incorporated in Karo syrup was not investigated. Possibly 
