90 Wisconsin Academy of Sciences, Arts, and Letters. 
Andrena thaspii 
Andrena cockerelli 
Andrena milwaukeensis 
Andrena viburnella 
Andrena aWofoveata 
S. Graenicher, Canadian Entomologist, 1903, 
p. 162. 
Andrena fragariana ) 
Andrena wheeleri L S. Graenicher, Entomological News, 1904, p. 64. 
Andrena persimilis \ 
Poly tropic and oligotropic bees. Some bees are in the habit 
of visiting a great variety of flowers, while others may be ob¬ 
served on the flowers of a single or those of a few species only. 
Loew 1 called the former polytropic and the latter oligotropic. 
Robertson ° states that “in the economy of the host-bees (those 
not inquiline) the most important flowers are those from which 
the female gets the pollen upon which her brood is fed.” Ac¬ 
cordingly he proposes to use the term oligotropic for a species 
of bee, of which the female obtains her pollen-supply from a 
single species, or several closely related species of plants, i. e., 
plants belonging to the same genus, or the same natural family, 
and on the other hand to call those bees polytropic that collect 
pollen from plants of different families. In considering the 
relations of our Andrena species to our flowers, I make use of 
the terms oligotropic and polytropic in the same sense as Robert¬ 
son. In the following table the time of flight, or in the case of 
insufficient observation the date of capture of each species is 
given, as also the names of the plants visited for pollen. When 
the bee has been recognized as oligotropic this is stated, other¬ 
wise the species is considered polytropic. Following Robertson’s 
example, I consider in the case of an oligotropic bee the latter 
adapted to the genus if found collecting pollen from more 
than one species of that genus, and to the family if it obtains 
pollen from plants belonging to different genera of that family. 
