1742 Hymenoptera in America North of Mexico 



blage which evolved from a sphecoid ancestor. Brothers (1975) has concluded that the sphecoid 

 wasps and bees belong to a single superfamily, the Sphecoidea, which according to him consists 

 of two informal groups, the Spheciformes (8 families) and the Apiformes (9 families). However, 

 Lanham (1960) has commented upon the similarities and differences of the Sphecoidea and 

 Apoidea and points out that the presence or absence of the strigil on the hind leg long known to 

 European hymenopterists may be of as much phylogenetic significance as other characters of 

 presumably phylogenetic importance. The value of the strigil in these matters was employed by 

 Boerner (1919) who divides the aculeate Hymenoptera into the Haplocnemata (ants, scolioid 

 wasps, and bees) and the Diplocnemata (sphecoids, pompilids, and vespids) thereby indicating 

 that bees are more closely related to the scolioids than to the sphecoid wasps. The phylogeny of 

 the Aculeata deserves a more thorough study and reevaluation before we can dismiss the possi- 

 bility that the Apoidea is a polyphyletic assemblage having been derived from both scolioid and 

 sphecoid ancestors. 



Most species of bees construct their nests in the ground usually excavating their own tunnels 

 and cells, although many others appropriate preexisting burrows or other cavities in the ground 

 and sometimes modify these to accompHsh their needs. Still many others make their nests above 

 ground. Among these are species that gnaw out their nesting tunnels in wood substrates of vari- 

 ous kinds including hollow stemmed plants, while others appropriate a wide variety of preexist- 

 ing cavities, such as abandoned beetle burrows, hollow trees, old mason wasp nests, old bird 

 nests, empty snail shells and old insect galls, while still others make their nests of wax and other 

 materials such as mud, resin, pebbles, pieces of leaves or petals, plant down, etc., and place their 

 nests either in the open attaching them to branches and so forth or place their nests under 

 eaves, bridges, rocks, cow chips and so on. As a consequence of these habits, many species of the 

 families Megachilidae and Apidae readily accept artificial nesting devices (hives, trap-nests, etc.) 

 which not only has made possible detailed studies of their biologies, but also has made possible 

 the manipulation and management of several species, including the common honeybee, for use in 

 the poUination of agricultural crops or for the production of honey and other useful products of 

 value and benefit to mankind. 



In nesting behavior the vast majority of bees are solitary including all members of the fami- 

 lies Colletidae, Oxaeidae and Melittidae. Except for a few communal species, all members of the 

 family Andrenidae also exhibit sohtary nesting behavior. Similarly most species of the family 

 Megachilidae are solitary in habit, although some nest communally (parasocial behavior) while 

 some are quasisocial and possibly a few are even semisocial in their nesting behavior. Among the 

 remaining three families (Halictidae, Anthophoridae and Apidae), the Halictidae and 

 Anthophoridae, each represented by many solitary species, contain some parasocial and eusocial 

 (primitively social) species as well as some subsocial species in the anthophorid tribe Ceratinini. 

 While most species of the family Apidae live in perennial, highly eusocial colonies, others exhibit 

 solitary, parasocial or primitively social nesting behavior. 



Bees are exceptionally important pollinators of both native vegetation and many agricultural 

 crops. Unquestionably bee-plant (bee-flower) relationships reflect various strategies on the part 

 of both sets of participants and two of the most commonly recognized behavioral modes of pollen 

 collection by bees are oligolecty and polylecty (see reviews by Grant, 1950; Linsley, 1958; and 

 Baker and Hurd, 1968). The intrafloral relationships of bees not only involves their own survival 

 and evolution, but also through coevolutionary interactions with flowers insures the main- 

 tenance and evolution of much of the earth's flora that depends upon entomophilous polHnation 

 for reproduction. These interrelationships are of unus'ial significance to us because we in turn 

 depend upon the earth's flora for our own livelihood and welfare. 



In America north of Mexico there are about 3,500 species of bees. This area represents nearly 

 one-sixth of the earth's land surface and, disregarding ecological diversity, this means that the 

 world fauna of bees approximates 21,000 species. Somewhat more than 2,700 of our species are 

 pollen-collecting bees while slightly more than 700 species (or about 21%) are cleptoparasitic spe- 

 cies. Only about 800 species of bees occur east of the Mississippi River and thus the apifauna of 

 the larger and more ecologically diverse western portion of America north of Mexico is more 

 than three times richer in species. Since it is well established that the apifaunas of arid regions 

 are consistently much richer in species than any other climatic regions, it is not surprising that 

 most of the North American species of bees are to be found in the southwestern United States 

 and adjacent northern Mexico. All eight recognized famihes of bees are present in America 

 north of Mexico and are represented by the following numbers of species: Colletidae (153), Ox- 



