140 Annals Entomological Society of America [Vol. VII, 
infestation. Leaves with broken petioles were found floating 
about early in the season before the galls had begun to turn 
yellow, but the greatest havoc from this cause was produced 
during the first week of August of the past year when the 
larve were pupating. At this time in one of the badly infested 
lily beds approximately 40% of the leaves were broken off 
and were floating about in a semi-decayed condition. 
The possibility of other insects playing a part in causing 
this deterioration of the petioles and the change in the color 
of the leaves was taken into account and, while other enemies 
were present, it was possible to observe many leaves and 
petioles which were infested only by the larva of H. confluens 
and which showed the same effects as those which happened to 
be affected by more than one enemy. 
All of the lily beds in the immediate vicinity of Douglas 
Lake were examined and the degree of infestation observed. 
There was considerable variation in this respect since some were 
only slightly infested while in others the percentage of infesta- 
tion was as high as 50 or 60. None were entirely exempt. 
It was found that the heaviest infestation occurred in a lily 
bed which was located at the end of a point which formed one 
-side of a protected bay and was thus exposed to the wind and 
- wave action to a greater extent than any of the other lily beds. 
In this particular case the infestation was almost twice as great 
in this exposed lily bed as in another in the protected bay only 
about one hundred feet away. The infestation in the lily 
beds in the beach pools and the sphagum bogs, which are 
protected from the action of the wind and waves, was very 
slight. The writer is not prepared at the present time to 
account for this distribution, but merely gives the facts for 
this particular region, realizing that the distribution just 
described may not agree with that of other regions. 
It thus appears that the larva of Hydromyza confluens 
is a serious enemy to Nymphaea americana since every petiole 
which contains even one larva is doomed. Three summers 
of work on insects infesting waterlilies in the Douglas Lake 
region has convinced the writer that, although there is a rather 
large number of species which attack this plant, yet Hydromyza 
confluens has only one rival for first place as the greatest enemy 
namely, the larve of Bellura melanopyga, one of the Noctuide, 
which also plays havoc in the lily beds. 
