178 SEVENTEENTH Report STATE ENTOMOLOGIST oF MINNESoTA—1918 
produce galls; but that probably gall growths are due in part at least 
to reactions between physiological processes of the plant tissue and the 
growing larva, which may absorb the sap at that particular part of 
the plant. 
Amongst gall flies, we find the occurrence of parthenogenesis dur- 
ing the summer; in fact, in many species the males have never been 
discovered. Out of many thousand galls of Cynips districtra and C. 
folii (28,000 or more) about 14,000 flies were raised; but all females. 
The fact has been thoroly established that in many of these in- 
sects we have an alteration of generations, one of the two being par- 
thenogenetic ; individuals of one generation are like their grandparents, 
not their parents. 
Packard says in this connection, “When we see a single oak hung 
with countless galls, the work of a single species, and learn how 
numerous are its natural enemies, it becomes evident that the demands 
for a great numerical increase must be met by extraordinary means 
like the generations of the summer broods of Plant Lice.” 
Referring again to the guest gall flies also found in galls, it may 
be said that frequently they resemble very closely the fly that makes 
the gall. In this connection, it may be stated that from a single species 
of gall, as many as 30 different kinds of insects (largely guest gall 
flies) have been obtained. 
Gall flies appear to be closely allied to the Chalcids and resemble 
them strikingly. Their bodies are flea-like; trochanters usually com- 
posed of a single joint; wings usually with a characteristic venation. 
See ice 63: 
FIGITIDAE 
Dorsal abdominal segments extending down along the sides and meeting beneath, 
enclosing or concealing the ventral segments or all the ventral segments except a part 
of the apical one. 
One species in this family is parasitic on the cabbage louse. 
Pseudocoelus gilletii Ashm. has been reared in Minnesota from 
puparia of Pegomyia brassicae. This is a most extensive family, well 
represented in North America. Without exception, as far as known, 
the species are all parasitic, principally upon larvae of Diptera, tho 
some prey upon aphids ard one is known to attack the larva of the 
lace-winged fly. 
