372 THE AMERICAN NATURALIST. |. [Vor. XXXIV. 
grua Walk. At the time the Iris flowers opened, these larvae 
were well grown. They then forsook the leaves, on which 
they had been feeding hitherto, for the daintier floral diet. 
Chetopsis enea Wied. and its Train.— This little bud- 
destroying ortalid fly deserves special mention, because in cer- 
tain situations it does more to prevent fruiting than all other 
insect enemies combined. Furthermore, its attack comes earli- 
est; its larva enters the pedicel at the base of the flower bud 
and bores downward into the common flowering stem (pe- 
duncle), killing not one bud, but the cluster of two or three 
arising at that point. Thus the flowers are killed before they 
open and are left to decay. 
Walking through a pasture near Lake Bluff, Ill., one day, I 
was led to examine some large clumps of flags by the very bad 
odor of their Chaetopsis-killed flowers. In clumps of several 
hundred plants each, not a single flower had been permitted 
to open. Finding Chetopsis larve still present in some of the 
pedicels, I collected a hundred or more terminal branches of 
the flower clusters and placed them on end in a jar, with a 
little water, some gravel, earth, etc., in the bottom, covered 
the jar with fine netting, and set it aside to await develop- 
ments. 
My little jar yielded, not a single species, but a little com- 
munity — a succession of interdependent forms, such as one 
often finds among insects with a brief life history, able to take 
advantage of a transient food supply. First there appeared a 
number of pomace flies (Drosophila phalerata Meig), which had 
probably been attracted to the buds by the souring of their 
saccharine juices. Next appeared the ortalids (Chetopsis «nea 
Wied.), the cause of all the trouble. These I found left the 
stems when full-grown larva and pupated on the wet soil in the 
bottom of the jar. By this time the rotting buds were teeming 
with oscinid larvae and studded all over the outside with pupe, 
from which soon issued swarms of the minute fly, Oscznzs soror 
Macq. With these also appeared a small number of beetles 
(undetermined) and a few parasitic Hymenoptera (Spalangia 
drosophile Ashm. and Heptamerocera sf.?). Finally, after the. 
decaying buds had been completely overrun with mycelial 
