148 SEVENTEENTH Report STATE ENtToMoLocist or MINNESoTA—1918 
ferred to as “grub” or “maggot” is generally, but not always (notably 
sawfly larva), footless. The pupal stage is quiescent and exhibits all 
the appendages of the adult enclosed in a pupal sheath. This pupa 
may or may not be contained in a cocoon. In the bees and wasps the 
pupal stage is passed in the comb. Of all the orders of insects, the 
Hymenoptera contains perhaps the most species and amongst them 
some forms which have a most important bearing upon man’s welfare. 
A student of Hymenoptera is impressed with the fact that apart 
from the highly useful activities of the honey bee, the two most 1m- 
portant and useful functions exhibited by the group are those of polli- 
nation or cross-fertilization so necessary in the production of good 
seed and good fruit, and of parasitism, by which characteristic 
the number of injurious insects is materially reduced. 
The modifications of flowers to bring about cross-fertilization by 
insects, and to prevent self-fertilization, are many and striking. In 
an observation covering twenty-six days, 275 species of insects were 
observed to visit the flowers of Pasturaca sativa; of these, 173 species 
belonged to Hymenoptera. Of 115 species of insects visiting milk- 
weed, 52 were Hymenoptera and 42 Diptera. Of 87 species observed 
on the flowers of willow during 7 days, 43 were Hymenoptera. It 
will be noted that this group is an important one in this connection. 
The services of Hymenoptera in the matter of parasitism have been 
referred to above. Suffice it to say that the Hessian fly, Tussock moth, 
scale insects, plant lice and a host of others are kept within bounds by 
the activity of hymenopterous parasites. These are chiefly occupied 
in destroying the tribes of vegetarian insects; 63 species attack a cer- 
tain species of moth; the American Tent Caterpillar is said to be para- 
sitized by 12 species of Hymenoptera, to say nothing of attacks upon 
them by Dipterous parasites. [From a single caterpillar of the Cab- 
bage Moth (Plusia brassicae) over 3,000 individuals of Copidosoma 
truncatellum have been bred by Girard. 
On the other hand, we find in this group, many injurious forms 
such as the larch sawfly and other sawflies and many gall makers. 
IXPLANATION OF COLORED PLATH 1 
Cimbex americana Leach. 
Trogus (Automalus) quebeccensis Prov. 
Perilampus hyalinus Say. 
Tetrachrysis caerulans F. 
Odynerus molestus Sauss. 
Vespula vulgaris L. 
Chalybion caeruleum L. 
AA Or WD 
