Vol. Xxiv] EXTOMOLOGICAL NK\\S. Ill 



deria cor data}. There is no other species of this genus of 

 bees found here. They are rather small bees with a weak 

 flight. As pollinators of the flowers they are much less im- 

 portant than bumble bees, which are present in large numbers 

 and make their visits very rapidly. The flowers are very 

 abundant and offer pollen, nectar and shelter. The nests of 

 these bees are probably close at hand. These are excellent 

 reasons why they should restrict their visits to the inflores- 

 cence of the pickerel weed. They cannot be influenced by 

 competition with any other species of Halictoides. 



The majority of oligotropic bees flying in summer and 

 autumn, whether they be species of Colletes, Andrena, Per- 

 dita, Panfrrginus or Melissodes, visit exclusively the Com- 

 positae. This course tends to produce competition, not to 

 lessen it. The large and crowded inflorescence consisting of 

 many small flowers which can be quickly and easily visited, 

 the great abundance of pollen and nectar, and the common- 

 ness and wide distribution of many species are the factors 

 which attract these bees. No other family of plants bloom- 

 ing at this season offers equal advantages. Jn a paper on 

 the bees of northwestern Wisconsin, Dr. Graenicher gives a 

 list of 30 oligotropic species, of which 19 get their pollen 

 from the Compositae. Many species of Perdita, according to 

 Professor Cockerell, are found only on the Compositae, 12 

 being taken on the flowers of Bigcloi'ia it'rightii. He fur- 

 ther states that there is a "relationship between the size of 

 the bees, the length-* of their tongues, and the kinds of flow- 

 ers." In Maine 3 species of Colletes, 5 of Andrena. i of Per- 

 dita, i of Pannrcjiinis, and 4 of Melissodes are oligotropic to 

 the Compositae; and at Carlinville, 111., a larger number of 

 species in all these genera (except Perdita} are reported by 

 Mr. Robertson to get their pollen from the inflorescence of 

 this family. The fact that so many species of bees are oligo- 

 tropic to the Compositae would seem alone to refute the the- 

 ory that this habit is an effort on their part to avoid competi- 

 tion by visiting different plant families. 



In conclusion it does not seem difficult to understand how 



