78 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



cysts of an unidentified small furcocercaria : and 

 many instances of heavy, severely damaginfj 

 Parorchis acanthits infection. Apparently no 

 other parasites are known. 



The only immediately available prospect for 

 development as a biolojrical control of Thah ap- 

 peared to be Parorchis acanthus, which is known 

 to damajre the drill severely and whose reported 

 adiilt hosts include several species of ojulls and 

 terns occurring in this area. Therefore, a study 

 of this parasite and its effect on the drill was 

 initiated. 



A preliminary report (1957) summarized avail- 

 able information on the life cycle, known liosts, 

 morphological descriptions, synonymy and en- 

 demic localities, and gave preliminary data on 

 experimental infection of drills, and incidence and 

 pathology of natural infections in Thavi. 



The present paper is a final report on P. acan- 

 thus and gives further information on life cycle, 

 experimental infections, and incidence and pa- 

 thology of natural infections in Gulf coast drills. 



Field collections of drills were made by Dr. 

 Abraham Fleminger, then at Bureau of Commer- 

 cial Fisheries Biological Laboratory, Galveston, 

 Texas; Dr. A. K. Sparks, then at Texas A. & M. 

 Research Foundation Laboratory, Grand Isle. 

 Louisiana; "William Demoran, Gulf Coast Re- 

 search Laboratoi-y, Ocean Springs, Mississippi; 

 and Eugene Holzapfel and others, Aransas Pass, 

 Texas. 



William D. "Wood, manager, Sanibel National 

 "Wildlife Refuge, Florida, supplied a number of 

 young laughing gulls used in infection studies. 



Consultations witli Dr. H. "W. Stunkard were 

 helpful during a part of the study. 



MATERIALS AND METHODS 



Specimens of T. haemastov%a from various local- 

 ities in Florida, Alabama, Mississippi, Louisiana, 

 and Texas, were examined for natural P. acanthus 

 infections by dissection or by isolation in individ- 

 ual di.shes of sea water. 



For morphological studie.s, both living and fixed 

 and stained material prepared by standard para- 

 sitological techniques were used.^ 



= Fixatives; G (Gilson). Z (Zenker), PFA-S (Allen's PFA-3 

 modification of Bnnin). Stains: DH-AzB-E (Delafield's hema- 

 toxylln-Azure B-Eosln Y), WH-AsB-E (Weigert's aeld-lpon- 

 chlorlde-hematoxylln-Azure B-Eosln Y). 



Juvenile herring gulls (La-rus argentatus) , ring- 

 billed gulls (i. deJawareTislt) and juvenile laugh- 

 ing gulls (Z. atriciJla) were used as experimental 

 hosts of adult womis. Experimental infection of 

 gulls was accomplished as follows. Cercariae were 

 permitted to encyst in a finger bowl of sea water 

 and become metacercariae. Tlie cysts, carefully 

 scraped from the bottom of a finger bowl with a 

 scalpel and suspended in a small amount of sea 

 water, were pipetted directly into the stomach of 

 a fasting bird by means of a stiff Vs-inch-bore 

 polyethylene tube carefully passed down the 

 esophagus. The tube was flushed with a few milli- 

 liters of sea water and carefully removed. The 

 bird was then returned to its cage and given its 

 daily feeding. Alternatively, cysts or adult worms 

 were introduced dii'ectly into the cloaca. 



Attempts to infect least tern {Sterna albifrons) 

 nestlings were made by feeding encysted metacer- 

 cariae with a pipette immediately before giving 

 the birds food. 



All gulls were fed chopped fish that had been 

 frozen and stored at 0° F. for several weeks to 

 prevent infecting the birds with fish-borne hel- 

 minths. Least tern nestlings were fed beef-base 

 dog food, later supplemented with bits of fish. 



If repeated examinations of cloaca and bursa 

 Fabricii over a period of weeks were consistently 

 negative, the gulls and terns were concluded to be 

 free of natural infection. The same method was 

 used to detect experimental infections, which, in 

 most cases, were subsequently confinned by 

 autopsy. 



Drills were infected experimentally by 24-hour 

 exposure of individuals to freshly hatched mira- 

 cidia in 4-inch bowls containing 100 ml. of sea 

 water. These drills were kept as long as 3 days 

 in 4-inch bowls with food and daily changes of 

 sea water, or for periods as long as 10 weeks in 

 battery jars with running sea water and adequate I 

 food. 



Thais specimens for histological study were 

 killed at various intervals after exposure to infec- 

 tion and fixed in Gilson's, Zenker's, Bouin's, or 

 Allen's PFA-3 solutions or Smith's modification 

 of Bouin's solution. Gilson's, Zenker's, and Allen's 

 PFA-3 gave best results. Specimens were paraf- 

 fin-embedded, sectioned at 7/* or 10^ and stained 

 routinely by a Delafield's hematoxylin-azure B- 

 eosin Y technique. "With the azure-eosin mixture 

 adjusted to pH 4.1 to 4.95 with Mcllvaine-Lillie 



