20 Journal oI Nematology, Volume 10, No. 1, January 1978

mum as controls of Meloidogyne incognita Economic Nematology, Academic Press, New and Pratylenchus alleni. J. Nemato]. 7:84-90. York. 563 p. 5. JENKINS, W. R. 1964, A rapid centrifugal- 11. SEINHORST, J. W. 1950. De betekenis van de flotation technique for separating nematodes toestand van de grond voor her optreden from soil. Plant Dis. Rep. 48:692. van de aantasting door bet stengelaaltje 6. MCBRYDE, M. C. 1936. A method of demon- (Ditylenchus dipsaci Kuhn Filipjev), Tijdschr. strating rust hyphae and haustoria in PIZiekt. 56:289-348. unsectioned leaf tissue. Am. J. Bot. 23:686-689. 12. SCHENCK, N. C., R. A. KINLOCH, and D. W. 7. POWELL, N. T. 1971. Interactions between DICKSON. 1975. Interaction of endomycor- nematodes and fungi in disease complexes. rhizal fungi and root-knot nematode on Annu. Rev. Phytopathology 9:253-274. soybean. Pages 607-617 in F. E. Sanders, 8. RONCADORI, R. W., and R. S. HUSSEY. 1977. B. Mosse, and P. B. Tinker, eds. Endomycor- Interaction of the endomycorrhizal fungus rhizas, Proceedings of a symposium held at Gigaspora margarita and root-knot nematode the University of Leeds, 22-25 July 1974. on cotton. Phytopathology 67:1507-1511. Academic Press, New York. 9. RUEHLE, J. L. 1973. Nematodes and forest 13. WILLIS, C. B. 1976. Effects of potassium fertil- trees: types of damage to tree roots. Annu. ization and Pratylenchus penetrans on yield Rev. Phytopathol. 11:99-118. and potassium content of red clover and 10. SASSER, J. N. 1972. Nematode diseases of alfalfa. J. Nematol. 8:116-121. cotton. Pages 187-214 in J. M. Webster, ed.

Drilomermis leioderma n. gen., n. sp. (Mermithidae:Nematoda) parasitizin 9 fimbriolafos (Say) (Dystiscidae:Coleoptera) GEORGE O. POINAR, JR., end JAMES J. PETERSEN1 Abstract: The nematode Drilomermis leioderma n. gen., n. sp. (Merrnithidae) is described from larvae of Cybister fimbriolatus (Say) (: Coleoptera) in Louisiana. Diagnostic characters of the genus Drilomermis are: medium-sized nematodes with the cuticle appearing smooth (lacking cross fibers) under the light microscope, six cephalic papillae, without mouth papillae, six hypodermal cords at midbody, 2 extremely long spicules (longer than 10 times body width at anus) which are separate and parallel (not twisted), an S-shaped vagina, medium-sized amphids located near head papillae, and postparasitic juvenile with a tail appendage. D. leioderma possesses a ventrally displaced mouth, very long vagina, and male genital papillae arranged in 3 double rows in the vicinity of the cloacal opening. Even when containing multiple parasites, about 40% of the hosts sulwived emergence of the memithids and lived several more days. In nature, some of these hosts may be able to continue their development, which is unusual since most mermithid-parasitized hosts die soon after the nematode emerges. Key Word: .

Members of the nematode family this nematode and discusses its relationship Mermithidae have rarely been encountered with other members of tile family. parasitizing in the family Dytiscidae (3). In fact, the only record o[ such an as- MATERIALS AND METHODS sociation was made in 1862, by Laboulbiene (1), who recorded a mermithid emerging Larvae of Cybister fimbriolatus (Say) from Dytiscus marginalis L. Thus, it was of (Dytiscidae:Coleoptera) parasitized by some interest when a species of Cybister was mermithid nematodes were collected from found parasitized by a mermithid nematode a pond, about 20 m in diameter and 0.5-1.0 in Louisiana. The present report describes m deep in Chloe, Louisiana. This perma- nent pond was sometimes nearly dry. Most Received for publication 10 June 1977. of the surface was covered with water-hyssop 1Division of Entomology and Parasitology, University of California, Berkeley, California 94720; and Gulf Coast [Bacopa caroliniana (Walt.) Robins], with Mosquito Research Laboratory, ARS, USDA, 803 Avenue soft rush (]uncus effusus L.) in the middle J, Lake Charles, Louisiana 70601, respectively. We thank Dr. Paul J. Spangler, National Museum of Natural His- and along the borders. Postparasitic stages tory, Washington, D.C., for identification of the host. of mermithid nematodes emerged from Mermithid from Cybister fimbriolatus: Poinar, Petersen 21 Cybister larvae collected in June 1976 and distance from tail tip to posterior portion May 1977. These nematodes were main- of trophosome 261 (211-323). tained in damp sand at 26-28 C, where they Male: (n = 10) (Figs. 1, 2, 5, 6, 8). molted, mated, and oviposited. Egg hatch- Length 1.76 (1.24-2.71) cm; greatest width ing occurred when the damp sand was 184 (140-220); distance from head to nerve flooded 2 or more weeks after oviposition. ring 275 (200-323); length amphidial pouch 13 (12-14); diameter amphidial RESULTS opening 5 (4-6); distance from head to vestigial excretory pore (?) 324 (216-385); Mermithids obtained from C. _tim- length of spicules 2130 (1210-2930); width briolatus were found to be new to science. of spicules 3-4; length of tail 155 (128-192); A description follows below. width of body at cloacal opening 136 (107- 169). Drilomerrnis n. gen. Preparasitie iuvenile: (Fig. 10) (n = 5). (Mermithidae Braun) Length 1000 (960-1040); greatest width 17 Diagnosis: Medium-sized nematodes (17-19). with adult cuticle appearing smooth (lack- Postparasitic juvenile: (n = 5). Tail ing cross-fibers) under the light microscope; bearing a small medium tail appendage 44 six head papillae; no mouth papillae; 6 (21-71) long. hypodermal cords at midbody; 2 extremely Type host: Cybister fimbriolatus (Say) long spicules (longer than 10 times body (Dytiscidae: Coleoptera). width at anus), separate and parallel; Type locality: Chloe, Louisiana. vagina S-shaped; amphids medium in size, Type species and specimen: Holotype located near head papillae; postparasitic (female) and allotype (male) deposited at juveniles with a tail appendage. Type spe- the Department of Nematology, University cies: Drilomermis leioderma n. sp. of California, Davis, CA. Paratypes de- Description: Medium-sized nematode posited in the collection of the senior with mouth shifted to the ventral side of author. the head; 6 cephalic papillae arranged in Diagnosis: A combination of characters- one plane; medium flask-shaped amphids, 6 cephalic papillae, 6 hypodermal cords, not connected by a commissure, opening lack of noticeable cross-fibers in the cuticle, just behind the cephalic papillae and situ- 2 long spicules, and S-shaped vagina-- ated on the dorsal side of the lateral clearly separates 1)rilomermis from other papillae; S-shaped vagina, very long; described mermithid genera. The genus spicules extremely long, more than 10 times Strelkovimermis Rubstov shares the above body width at cloaca, paired, separate, characters but has paired spicules about narrow; genital papillae arranged in 3 equal to the anal body width. The only double rows near cloacal opening; post- genus of mermithids characterized by parasitic juvenile with small tail appendage; spicules equal to those of Drilomermis is female tail bluntly rounded. Amphimermis. The latter genus, however, In the following quantitative descrip- contains spicules characteristically twisted tion, all measurements are in microns around each other, and the cuticle contains except as specified otherwise. The first visible cross-fibers. Also, all of the species of figure represents the average value and the Amphimermis have terminal mouths, except range is given in parentheses. A. tinyi Nickle (2), which is incompletely Females: (n = 6) (Figs. 3, 4, 7). Length described and for the present must be re- 4.59 (3.82-5.68) cm; greatest width 310 garded as a species inquirendarum. (280-360); distance from head to nerve ring Biological observations: Only larvae of 326 (280-400); length amphidial pouch 13 C. fimbrioIatus were found harboring D. (11-15); diameter amphidial opening 7 leioderma in the pond sampled, and the (6-9); length S-shaped vagina 1093 (800- incidence of parasitism in four separate 1200); %V 44 (36-49); greatest diameter of collections ranged from 33 to 80%. eggs 83 (65-95); remnant cloacal opening Parasitic development probably lasts 202 (184-216) from tail tip; vestigial ex- for 3-5 weeks since collected infected hosts cretory pore (?) 365 (308-423) from head; were held in the laboratory for up to 3 22 ]ournal ol Nematology, Volume 10, No. 1, january I978

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lOJ Mermithid from Cybister fimbriolatus:_Poinar, Petersen 23 weeks before the parasites emerged. When limited (only 15 infected hosts were ex- hosts had multiple infections, the nema- amined), parasite loads had a noticeable todes emerged over a period of several days. effect on the sex ratios of the emerging For instance, four nematodes escaped from nematodes. Hosts with single or dual infec- one host on the first 2 days of emergence, tions produced only female nematodes, an additional five emerged during the next whereas hosts with four or more parasites 6 days, and two more left on the ninth and produced a predominance of male post- tenth day. The host died on the ninth day parasites. and retained one last nematode. Abont 40% of the hosts survived emergence of LITERATURE CITED their parasites and lived several more days. 1. LABOULBIENE, J. J. A. 1862. Note sur les In nature, some of these hosts may be able helminthes parasites du genre Mermis sortis to continue normal development, which is du corps du Gryllus domesticus et du Dytiscus very unusual since most mermithid- marginalis. Ann. Soc. Entomol. Fr. 2:576-578. parasitized hosts die soon after the 2. NICKLE, W. R. 1972. A contribution to our nematode emerges. knowledge of the Mermithidae (Nematoda). J. Nematol. 4:113-146. Parasite densities averaged 5.2 (1-17) 3. POINAR, JR.. G. O. 1975. Entomogenous Nema- per host (one host with 17 worms died todes. E. J. Brill, Leiden, 317 pp. prematurely). Though observations were

Illll \\\\N FIG. 1-10. Drilomermis leioderma n. gen., n. sp. 1) Ventral view of male head. 2) Enface view of male. 3) Lateral view of female. 4) Lateral view o£ vulvar area. 5) Lateral view of male tail. 6) Ventral view of male tail. 7) Lateral view of female tail. 8) Cross section of male at midbody. O) Lateral view of tail of a parasitic juvenile ready to leave host. 10) Infective-stage juvenile.