Experimental studies on morphological variation in the cestode genus Hymenolepis. 1. Morphology and development of the cysticercoid of H. nana in Tribolium confusum

Abstract

1. 1. The growth and development of the cysticercoid of Hymenolepis nana, as observed in experimentally infected Tribolium confusum, have been described. 2. 2. Attempts to induce hatching of the egg of H. nana, in vitro, were unsuccessful. Eggs hatched in the mid-gut of T. confusum within 2 hours after ingestion. Liberation of the hexacanth embryo seemed to be dependent upon hook action as well as upon some property common to both the invertebrate and vertebrate hosts. 3. 3. Development of the embryo to an infective cysticercoid required about 192 hours in beetles maintained at a constant temperature of 28 degrees C. The scolex was retained within the capsule throughout the developmental period. 4. 4. Cysticercoids also completed their development in the larva of T. confusum and survived metamorphosis of this insect. 5. 5. Experimental infections were successfully established in Tribolium castaneum, Dermestes ?lardarius, Sitophylus oryza and Galleria mellonella, but not in Periplaneta americana, Passalus cornutus nor Tenebrio molitor. The infections in D. lardarius, S. oryza and G. mellonella constitute new intermediate host-records for this species. 6. 6. Except for size of the cercomer, no differences in the morphology of cysticercoids from the different insect species were observed. Size of the cercomer appeared to be correlated with the size of the insect hemocoele. 7. 7. A crowding effect was manifested when 50 or more cysticercoids were present in T. confusum. 8. 8. Starvation of T. confusum before and during development of the cysticercoid had no apparent effect on the prevalence of infection, but significantly more abnormal cysticercoids were found in starved as compared with non-starved beetles.