REVISION OF STREPSIPTERA PIERCE. 41 



Social insects. — The remainder of the vespoid hosts fall under this 

 category. They build large nests and observe a division of labor. 

 Triungulinids may with ease pass from their maternal host to the cell 

 of a new larva. Fertilization of the parasites probably takes place 

 among the swarm at the nest. 



Here also fall the formicid hosts, which practice division of labor 

 in subterranean nests. Since little is known of the parasitism of ants, 

 the discussion can go no farther. 



b. Food habits of adult hosts. — Spermophagous insects. — Among the 

 seed-eating insects may be noted only the ants. As the transfer of the 

 triungulinids probably occurs on the ground or in the nests no signifi- 

 cance is noticed in the food habit. 



Predaceous insects. — The ants belong also under the head of pre- 

 daceous insects. Here also may be classed all of the Sphecoidea and 

 the Eumenidflp. These wasps are all philotropic and will be more 

 fully discussed under that heading. 



Herbivorous insects. — This group includes the Gryllotalpidse, 

 Scutellaridse, and Homoptera. Apropos of the Homoptera, Osborn 

 and Ball (1897) write: 



The species of Jassidte have, as a rule, a decided limitation as to food plant, usually 

 holding closely to one species of plant, almost invariably limited to one plant for breed- 

 ing, but feeding more indiscriminately in mature stages. 



This statement may be applied to most, if not all, of the homop- 

 terous hosts thus far recorded. It may be readily seen that where an 

 insect is confined to certain definite food plants the transfer of triun- 

 gulinids can be much more easily accomplished than where the hosts 

 are indiscriminate feeders. 



Philotropic insects. — The majority of the hosts known are flower 

 frequenters, and as such are classed as oligotropic when visiting a single 

 species, genus, or family of flowers, and polytropic when visiting many 

 genera or families of flowers. It is very reasonable to infer that the 

 most ordinary method of transfer of triungulinids takes place at 

 flowers, because of the analogous forms of strepsipterous and rhipi- 

 phorid triungulinids. Most of the wasps are flower visitors, because 

 they may quench their thirst in the nectarine liquids. They are con- 

 sequently polytropic; but the bees are more highly developed and 

 often specially adapted for particular flowers, hence many of them are 

 oligotropic. In this connection the following table may be introduced, 

 giving the range, season, and flower records of the most important 

 hosts of Stylops in North America. The list is compiled from the 

 writings of Charles Robertson, Sigmund Graenicher, T. D. A. Cocker- 

 ell, and Henry L. Viereck, and from records of J. C. Crawford, and host 

 records in possession of the writer, referred to at numerous places in 

 the text. The species are arranged according to season. 



