larvae of Cybister fimbriolatus (Say) (Dytiscidae: Coleoptera) in Louisiana. Diagnostic characters ... J, Lake Charles, Louisiana 70601, respectively. We thank.
20 Journal oI Nematology, Volume 10, No. 1, January 1978
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7.
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9. 10.
mum as controls of Meloidogyne incognita and Pratylenchus alleni. J. Nemato]. 7:84-90. JENKINS, W. R. 1964, A rapid centrifugalflotation technique for separating nematodes from soil. Plant Dis. Rep. 48:692. MCBRYDE, M. C. 1936. A method of demonstrating rust hyphae and haustoria in unsectioned leaf tissue. Am. J. Bot. 23:686-689. POWELL, N. T. 1971. Interactions between nematodes and fungi in disease complexes. Annu. Rev. Phytopathology 9:253-274. RONCADORI, R. W., and R. S. HUSSEY. 1977. Interaction of the endomycorrhizal fungus Gigaspora margarita and root-knot nematode on cotton. Phytopathology 67:1507-1511. RUEHLE, J. L. 1973. Nematodes and forest trees: types of damage to tree roots. Annu. Rev. Phytopathol. 11:99-118. SASSER, J. N. 1972. Nematode diseases of cotton. Pages 187-214 in J. M. Webster, ed.
Economic Nematology, Academic Press, New York. 563 p. 11. SEINHORST, J. W. 1950. De betekenis van de toestand van de grond voor her optreden van de aantasting door bet stengelaaltje (Ditylenchus dipsaci Kuhn Filipjev), Tijdschr. PIZiekt. 56:289-348. 12. SCHENCK, N. C., R. A. KINLOCH, and D. W. DICKSON. 1975. Interaction of endomycorrhizal fungi and root-knot nematode on soybean. Pages 607-617 in F. E. Sanders, B. Mosse, and P. B. Tinker, eds. Endomycorrhizas, Proceedings of a symposium held at the University of Leeds, 22-25 July 1974. Academic Press, New York. 13. WILLIS, C. B. 1976. Effects of potassium fertilization and Pratylenchus penetrans on yield and potassium content of red clover and alfalfa. J. Nematol. 8:116-121.
Drilomermis leioderma n. gen., n. sp. (Mermithidae:Nematoda) parasitizin 9 Cybister 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) (Dytiscidae: 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: taxonomy.
Members of the nematode family Mermithidae have rarely been encountered parasitizing beetles in the family Dytiscidae (3). In fact, the only record o[ such an association was made in 1862, by Laboulbiene (1), who recorded a m e r m i t h i d emerging from Dytiscus marginalis L. Thus, it was of some interest when a species of Cybister was found parasitized by a mermithid nematode in Louisiana. T h e present report describes Received for publication 10 June 1977. 1Division of Entomology and Parasitology, University of California, Berkeley, California 94720; and Gulf Coast Mosquito Research Laboratory, ARS, USDA, 803 Avenue J, Lake Charles, Louisiana 70601, respectively. We thank Dr. Paul J. Spangler, National Museum of Natural History, Washington, D.C., for identification of the insect host.
this nematode and discusses its relationship with other members of tile family. M A T E R I A L S AND M E T H O D S Larvae of Cybister fimbriolatus (Say) (Dytiscidae:Coleoptera) parasitized by mermithid nematodes were collected from a pond, about 20 m in diameter and 0.5-1.0 m deep in Chloe, Louisiana. This permanent pond was sometimes nearly dry. Most of the surface was covered with water-hyssop [Bacopa caroliniana (Walt.) Robins], with soft rush (]uncus effusus L.) in the middle and along the borders. Postparasitic stages of mermithid nematodes emerged from
Mermithid from Cybister fimbriolatus: Poinar, Petersen 21
Cybister larvae collected in June 1976 and May 1977. These nematodes were maintained in damp sand at 26-28 C, where they molted, mated, and oviposited. Egg hatching occurred when the damp sand was flooded 2 or more weeks after oviposition. RESULTS Mermithids obtained from C. _timbriolatus were found to be new to science. A description follows below.
Drilomerrnis n. gen. (Mermithidae Braun) Diagnosis: Medium-sized nematodes with adult cuticle appearing smooth (lacking cross-fibers) under the light microscope; six head papillae; no mouth papillae; 6 hypodermal cords at midbody; 2 extremely long spicules (longer than 10 times body width at anus), separate and parallel; vagina S-shaped; amphids medium in size, located near head papillae; postparasitic juveniles with a tail appendage. Type species: Drilomermis leioderma n. sp. Description: Medium-sized nematode with mouth shifted to the ventral side of the head; 6 cephalic papillae arranged in one plane; medium flask-shaped amphids, not connected by a commissure, opening just behind the cephalic papillae and situated on the dorsal side of the lateral papillae; S-shaped vagina, very long; spicules extremely long, more than 10 times body width at cloaca, paired, separate, narrow; genital papillae arranged in 3 double rows near cloacal opening; postparasitic juvenile with small tail appendage; female tail bluntly rounded. In the following quantitative description, all measurements are in microns except as specified otherwise. The first figure represents the average value and the range is given in parentheses. Females: (n = 6) (Figs. 3, 4, 7). Length 4.59 (3.82-5.68) cm; greatest width 310 (280-360); distance from head to nerve ring 326 (280-400); length amphidial pouch 13 (11-15); diameter amphidial opening 7 (6-9); length S-shaped vagina 1093 (8001200); %V 44 (36-49); greatest diameter of eggs 83 (65-95); remnant cloacal opening 202 (184-216) from tail tip; vestigial excretory pore (?) 365 (308-423) from head;
distance from tail tip to posterior portion of trophosome 261 (211-323). Male: (n = 10) (Figs. 1, 2, 5, 6, 8). Length 1.76 (1.24-2.71) cm; greatest width 184 (140-220); distance from head to nerve ring 275 (200-323); length amphidial pouch 13 (12-14); diameter amphidial opening 5 (4-6); distance from head to vestigial excretory pore (?) 324 (216-385); length of spicules 2130 (1210-2930); width of spicules 3-4; length of tail 155 (128-192); width of body at cloacal opening 136 (107169). Preparasitie iuvenile: (Fig. 10) (n = 5). Length 1000 (960-1040); greatest width 17 (17-19). Postparasitic juvenile: (n = 5). Tail bearing a small medium tail appendage 44 (21-71) long. Type host: Cybister fimbriolatus (Say) (Dytiscidae: Coleoptera). Type locality: Chloe, Louisiana. Type species and specimen: Holotype (female) and allotype (male) deposited at the Department of Nematology, University of California, Davis, CA. Paratypes deposited in the collection of the senior author. Diagnosis: A combination of characters6 cephalic papillae, 6 hypodermal cords, lack of noticeable cross-fibers in the cuticle, 2 long spicules, and S-shaped vagina-clearly separates 1)rilomermis from other described mermithid genera. The genus Strelkovimermis Rubstov shares the above characters but has paired spicules about equal to the anal body width. The only genus of mermithids characterized by spicules equal to those of Drilomermis is Amphimermis. The latter genus, however, contains spicules characteristically twisted around each other, and the cuticle contains visible cross-fibers. Also, all of the species of Amphimermis have terminal mouths, except A. tinyi Nickle (2), which is incompletely described and for the present must be regarded as a species inquirendarum. Biological observations: Only larvae of C. fimbrioIatus were found harboring D. leioderma in the pond sampled, and the incidence of parasitism in four separate collections ranged from 33 to 80%. Parasitic development probably lasts for 3-5 weeks since collected infected hosts were held in the laboratory for up to 3
22 ]ournal ol Nematology, Volume 10, No. 1, january I978
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M e r m i t h i d from Cybister fimbriolatus:_Poinar, Petersen 23 weeks before the parasites emerged. W h e n hosts h a d m u l t i p l e infections, the n e m a todes e m e r g e d over a p e r i o d of several days. For instance, four n e m a t o d e s escaped from o n e host o n the first 2 days of emergence, a n a d d i t i o n a l five e m e r g e d d u r i n g the n e x t 6 days, a n d two m o r e left o n the n i n t h a n d t e n t h day. T h e host d i e d o n the n i n t h day a n d r e t a i n e d one last n e m a t o d e . A b o n t 4 0 % of the hosts s u r v i v e d e m e r g e n c e of their parasites a n d lived several m o r e days. I n n a t u r e , some of these hosts m a y be able to c o n t i n u e n o r m a l d e v e l o p m e n t , w h i c h is very u n u s u a l since most mermithidparasitized hosts die soon after the n e m a t o d e emerges. Parasite densities averaged 5.2 (1-17) per host (one host w i t h 17 w o r m s d i e d p r e m a t u r e l y ) . T h o u g h o b s e r v a t i o n s were
l i m i t e d (only 15 i n f e c t e d hosts were exa m i n e d ) , p a r a s i t e loads h a d a n o t i c e a b l e effect o n the sex ratios of the e m e r g i n g n e m a t o d e s . Hosts w i t h single or d u a l infections p r o d u c e d o n l y female n e m a t o d e s , whereas hosts w i t h four or m o r e parasites p r o d u c e d a p r e d o m i n a n c e of m a l e postparasites. LITERATURE
CITED
1. LABOULBIENE, J. J. A. 1862. Note sur les helminthes parasites du genre Mermis sortis du corps du Gryllus domesticus et du Dytiscus marginalis. Ann. Soc. Entomol. Fr. 2:576-578. 2. NICKLE, W. R. 1972. A contribution to our knowledge of the Mermithidae (Nematoda). J. Nematol. 4:113-146. 3. POINAR, JR.. G. O. 1975. Entomogenous Nematodes. E. J. Brill, Leiden, 317 pp.
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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.
