320 ENTOMOLOGICAL NEWS. [July, '14 



tongue appears to have increased or decreased according as 

 the total size of the bee has increased or decreased, not to 

 meet special requirements. Species of Perdita visit the flow- 

 ers of both Verhesina and Bigelovia, but the species on the 

 flowers of the former are much larger than those on the latter. 

 The species of Perdita on Gutierresia are still smaller than 

 those on Bigelovia. The visitors of the Compositae according 

 to Graenicher, are determined by tube-length more than by 

 any other character of the flower ("Wisconsin Flowers and 

 their Pollination," Bull. Wis. Nat. Hist. Soc, 7:42.) Thus 

 it is the tube-length of the flower, not competition, which is 

 the factor limiting the visits of many species of Perdita. The 

 facts related, as well as many others, are well in accord with 

 the views of the writer. (On Perdita, see Cockerel!, "The Bees 

 of the Genus Perdita," Pr. Ac. Nat. Sci. Phil., 48:25-107; 

 "Notes on New Mexican Flowers and their Insect Visitors," 

 Bot. Gaz., 24: 104-6; "A List of the Bees of the Genus Per- 

 dita," Psyche, 18: 134-43. Also Graenicher, "Wisconsin Bees 

 of the Genus Perdita," Can. Ent., 46: 51-7.) 



The female inquiline bees do not gather pollen and nectar 

 for brood-rearing, but like the males of the nest-builders re- 

 quire only nectar for themselves — the males of the honey bee 

 are even unable to feed themselves. Under these circum- 

 stances it should not be expected that they will exhibit the 

 same constancy to flowers as the brood-rearing species. 

 Nevertheless a number of the parasitic bees with a short term 

 of flight visit wholly or largely the Compositae. and under 

 Loew's definition would be called oligotropic species. This is 

 of great interest since it is not claimed that they have acquired 

 this habit as the result of competition. 



According to the theory proposed by the writer certain bees 

 have become oligotropic because of the direct advantage gain- 

 ed, combined with the fact that their flight was synchronous, 

 or nearly so, with the period of inflorescence of the plant to 

 which they restricted their visits. This theory offers an ex- 

 planation of the rise of oligotropism by the observation of ex- 

 isting conditions. There may be and often are accessory fac- 



