Vol. XXV] ENTOMOLOGICAL NEWS. 73 



and inconvenient flowers. It would be distinctly disadvantage- 

 ous for it to limit itself to some particular flowers and exceed- 

 ingly unlikely that it would do so. The ecological specializa- 

 tion exhibited by Anthedon, Verbenapis and other oligotropes 

 is a fairly certain indication of the pressure of competition. 



I think that the long-tongued pygidial bees were developed 

 as competitors of the bumblebees, the first on the ground and 

 the most polytropic of bees. I think this explains why they 

 have a comparatively short and rapid flight and so frequently 

 oligotropic habits. In a similar way the Andrenidae, Panur- 

 gidae and related groups which are so often oligotropic were 

 probably preceded by the Halictidae, the most polytropic of 

 short-tongued bees. There are forty species of Halictidae fly- 

 ing throughout the season. In the spring there are the females 

 which have passed through the winter, but later both sexes of 

 the regular brood are flying so that the maximum is late. There 

 are ninety-four other short-tongued bees occupying the same 

 region. It would be a hard matter for all of these bees to fly 

 throughout the season and compete with the Halictidae. In- 

 stead they have short times of flight and are distributed 

 so that not more than fifty-two are flying in any month 

 and these only in the spring when the Halictidae are least 

 abundant. And these bees are the least abundant when the 

 Halictidae are the most abundant and most active. The early 

 maximum, the short flight, the non-competitive phenological 

 distribution, and the frequently oligotropic habits indicate that 

 these bees have managed to hold their own only by dividing 

 up the remaining field and occupying the most favorable cor- 

 ners left by their perennial polytropic competitors. 



To the list of local oligotropes add: Petalostemon viola- 

 ceus: Colletes albescens, robertsonii ; Strophostytes angnlosa: 

 Megachile strophostylis ; Papilionaceae: Meg. generosa, 

 Cinathodon georgicus, Anthidium psoraleae, Synalonia atri- 

 ventris, fuscipes ; Sali.v : Andrena salicacea, macoupinensis ; 

 Nymphaeaceae : Chloralictus nymphaearum ; Cassia chamae- 

 crista: Melissodes atripes ; Ipomoca pandurata: Cemolobus 

 ipomoeae. 



