Previous workers at Cultus Lake discovered a new species of Schistosome cercaria. In the present attempts to find this cercaria and to elucidate its life cycle, four completely different dermatitis-producing forms were discovered, two of which are considered new species. The other two may be new. Three of the cercariae are described in detail. These are the cercaria of Trichobilharzia adamsi n.sp., Cercaria chilliwackensis n.sp. and Cercaria 10 which may be a new species. The description includes morphology, behavior, snail hosts, dermatitis-producing ability, and observations on the sporocysts of these forms. All were found to be capable of producing Schistosome dermatitis. Therefore two and possibly three more cercariae have been added to the list of known dermatitis-producers. The three cercariae were found in specific areas along the north-west shoreline of Cultus Lake. Attempts were made to complete the life cycle of the three cercariae. Two approaches were adopted. Animals were trapped within the areas at which the cercariae were found, but examination showed that they did not possess adult Schistosomes. Laboratory experiments were carried out in which animals were subjected to the various cercariae and later examined for adult worms. An immature female worm was recovered from a domestic duck which had been exposed to cercariae. The worm, Trichobilharzia adamsi, is described as a new species. Part of the life cycle of this trematode is described. The domestic duck was established as a definitive host under experimental conditions. The specific definitive host of the trematode at Cultus Lake was not determined. The cercaria of T. adamsi is placed in the "ocellata group" on the basis of its morphology. Cercaria chilliwackensis is placed along with Cercaria douthitti in the "douthitti group". Cercaria 10 is very similar to the cercaria of Gigantobilharzia huronensis, and is placed with the latter in the "spindalis group". All three of the cercariae described possess papillar spination. These spines have been described only once in the past as occuring on a dermatitis-producing cercaria. The papillar supination is described in detail. The spines are located in similar patterns on the bodies of the three cercariae. This pattern is carried through to the adult of T. adamsi. Evidence is given of the occurance of papillar spination on cercariae elsewhere in the Province. A modification of the perfusion technique of Yolles et al is described. This was used for the investigation of the experimental animals for adult worms. Further, a new technique using the side-arm flask of McMullen and Beaver is described. The apparatus concentrates Schistosome cercariae in large numbers in a relatively small area. / Science, Faculty of / Zoology, Department of / Graduate

Thesis (Ph. D.)--University of Michigan, 1940. / Caption title. Thesis note on slip mounted on p. 171. "Contribution from the Department of Zoology, University of Michigan." "Reprinted from Transactions of the American Microscopical Society, vol. LX, no. 2, April, 1941." Bibliography: p. 208-210.

Thesis (Ph. D.)--University of Michigan, 1940. / Cover title. "Contribution from the Department of zoology, University of Michigan." "Reprinted from Transactions of the American microscopical society, vol. LX, no. 2, April, 1941." Bibliography: p. 258-260.

The host/parasite association between the pulmonate snail Stagnicola elodes and the digenean Plagiorchis elegans was examined with a view to identifying some of the biotic and abiotic factors that govern parasite egg development, infectivity and survival, the dynamics of cercarial production, as well as host susceptibility to infection, growth, reproduction and mortality. Plagiorchis elegans eggs passed with the feces of the hamster (Mesocricetus auratus) experimental definitive host were unembryonated. Between 0 and 30 C, the rate of embryonation continued to increase with temperature, whereas infectivity and survival were optimal between 10 to 20 C. Light adversely affected embryonation. Parasite acquisition increased with the intensity of exposure and sexual maturity. Infection invariably enhanced pre-patent host growth in a dose-dependent manner. Cercarial production increased with time and reached a plateau. Snails infected prior to sexual maturity released more cercariae than mature individuals. Heavily infected snails tended to die prematurely regardless of age at infection and parasite dose, thereby reducing their total production of cercariae to levels below those of more lightly infected individuals. Even light infections castrated the snail host. Snails infected when immature never reproduced, whereas reproductive snails ceased egg production within days of infection. Similar effects were observed in the incompatible snail host Biomphalaria glabrata, although no cercariae were ever produced. Both enhanced growth and parasitic castration are attributable to the mother sporocyst.

This study documents dynamic changes in the mean abundance and body size of arthropods in an ephemeral pond over the course of a summer in order to understand the nature of interactions that shape this community, and to assess the risks posed by exposure to cercariae of the entomopathogenic digenean, Plagiorchis elegans, a potential control agent for larval mosquitoes. Chironomids were the most abundant, comprising almost two-thirds of all arthropods collected; they were followed by chaoborids, the most abundant predator. Other arthropods, in decreasing order of abundance, were the ephemerids, isopods, amphipods, odonates, dytiscids, and hemipterans. Infections were found only in chironomids and were extremely rare and of low intensity, conceivably due to predation of chaoborids on cercariae and may have protected the community from exposure to these parasites. Findings are discussed in terms of using entomopathogenic digeneans as agents in the biological control of mosquitoes.

This study deals with the cercarial fauna of marine mollusks in the littoral zone and estuaries of the California coast between Duxbury Reef and Fort Ross. The investigation began in June, 1968 at the Pacific Marine Station, Dillon Beach, California and continued through July, 1969, with monthly collections at various localities (see map). Two major objectives were aimed at: first, to continue a survey of the cercariae of the area begun by Fisk (194) and second, to establish a basis for future life history studies.

No description available.

No description available.

Parasites exert substantial costs on their hosts. Thus, natural selection should favour behavioural defenses that reduce hosts’ exposure to parasites. This prediction has rarely been tested for aquatic hosts exposed to parasites. I designed experiments to test if fathead minnows could detect cercariae of the trematode, Ornithodiplostomum sp. and engage in antiparasite behaviours to avoid them. Minnows exposed to cercariae formed 20.1% tighter shoals compared to water controls. Further, minnows greatly reduced their overall activity, but only when they were exposed for a second time. The latter result is important because it provides the first indication that hosts can learn to avoid parasites. Lastly, I tested if epidermal club cells play a defensive role against cercariae. Club cells did not, but other components of the epidermis, probably mucus cells, decreased cercarial infectivity by 61-68%. My results show that fish can detect, learn, and ultimately avoid aquatic larval stages of parasites. / 105 leaves : ill. ; 29 cm.

The effect of Plagiorchis elegans cercariae on the vertical distribution of second, third, and fourth instar larvae of Aedes aegypti in the water column was studied in the laboratory. Under daytime conditions and in the absence of the parasite, larvae divided their time between the top and bottom of the water column. At night larvae spent the majority of their time at rest at the top of the column. In the presence of P. elegans cercariae larvae spent more time at rest at the surface under daytime conditions but increased their active time at the bottom under nighttime conditions. The presence of cercariae elicited escape and grooming responses and tended to reduce and fragment feeding activity.