Pheromermis myopis sp. n. (Nematoda: Mermithidae), a Parasite of Tabanus punctifer (Diptera: Tabanidae)

Abstract

Pheromermis myopis sp. n., which parasitizes larvae of the horse fly, Tabanus punctifer Osten Sacken, is described from northern California. This is the first mermithid species to be described from a North American tabanid. The eggs of P. myopis are unembryonated when laid but develop into infective stage juveniles in approximately 3 weeks at 20 C. Eggs hatched when ingested by 3rd instars of an experimental mosquito host, Culex pipiens pipiens L., and the mermithid juveniles penetrated the gut wall of the mosquito larvae and attempted to encyst in their tissues. Because none of the eggs of P. myopis hatched when kept in water for 4 months, we believe that this species probably has an indirect developmental cycle involving a paratenic host. Previous records of Mermithidae (Nematoda) as parasites of Tabanidae (Diptera) have been cited by Poinar (1975). Recently, Rubtsov and Andreeva (1974) described Paramermis tabanivora and Gastromermis macrosoma from Hybomitra sp. and Tabanus autumnalis L., respectively. In addition, Paramermis hybomitrae was described from Hybomitra arpadi Szilady (Rubtsov and BeyBienko, 1974) and Amphibiomermis turgenica from Hybomitra sp. (Rubtsov and Vakker, 1973). While studying the immature stages of Tabanidae in northern California, one of us (RSL) observed nematodes in larvae of Tabanus punctifer Osten Sacken. The present paper describes this nematode and discusses some aspects of its life history. MATERIALS AND METHODS Parasitized larvae of Tabanus punctifer and free-living mermithids were collected from the border of a stock pond located at Castle Rock Park in Walnut Creek, Contra Costa County, California, 1975-77. The pond was spring fed and normally contained water throughout the year. About half of the pond's border was adjacent to fields containing cattle. The remainder of the edge contained cattail (Typha sp.). The pond was approximately 20 m in diameter and 1 m deep in the center. Larvae of T. punctifer and mermithid nematodes were extracted from moist soil bordering the pond by handsorting samples taken with a trowel. Other invertebrates also were extracted from soil above the pond margin by handsorting Received for publication 27 September 1977. * Division of Entomology and Parasitology, University of California, Berkeley, California 94720. t Vector and Waste Management Section, California Department of Health, Berkeley, California 94704. samples or placing them in Berlese funnels for several days. The tabanid larvae and their invertebrate associates were examined for the presence of mermithids with a dissecting microscope. Larval tabanids were identified by comparison with previously published descriptions and figures (Webb and Wells, 1924; Lane, 1975) and confirmed by rearing several specimens to adults. Parasitized tabanid larvae were maintained individually in petri dishes containing approximately 1 cm of mud in the bottom. Upon emergence of the parasite, the tabanid was removed for observation and the nematode kept in the original container until it had molted and reached the adult stage. Adult nematodes then were placed in water for mating and oviposition. For descriptive purposes, the nematodes were fixed in TAF and processed to glycerin using the simple evaporation method (Poinar, 1975). Laboratory infections were acheived by placing nematode eggs with 3rd instars of the northern house mosquito, Culex pipiens pipiens L. (Diptera: Culicidae).