Host Specificity of Various Species of Crithidia Leger

Naturally entozoic species of Crithidia are capable of establishing parenteral infections as demonstrated by the behavior of Crithidia harmosa, C. arili, C. acanthocephali, C. fasciculata, C. onco- pelti, and C. luciliae in the hemocoel of Drosophila virilis, Tenebrio molitor, and Acheta domesticus. Drosophila virilis was fatally susceptible to each species of Crithidia. Infections in T. molitor were marked by some intra- and interspecific variation; C. fasciculata was consistently lethal. Multiplication of the flagellates was comparatively limited in A. domesticus. In no instance was there any indication of a consistent type of grouping of the species of Crithidia in relation to the three types of hosts em- ployed, but rather, differences were expressed between each species of flagellate. Cellular defense was initiated by each species of insect in response to Crithidia; encapsulation occurred in some T. molitor and A. domesticus. Peroral introduction of Crithidia with few exceptions was not successful.