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John Janovy Publications Papers in the Biological Sciences

2-1999

The Life Cycle of a Horsehair Worm, Gordius robustus (Nematomorpha: Gordioidea)

Ben Hanelt University of New Mexico, [email protected]

John J. Janovy Jr. University of Nebraska - Lincoln, [email protected]

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Hanelt, Ben and Janovy, John J. Jr., "The Life Cycle of a Horsehair Worm, Gordius robustus (Nematomorpha: Gordioidea)" (1999). John Janovy Publications. 9. https://digitalcommons.unl.edu/bioscijanovy/9

This Article is brought to you for free and open access by the Papers in the Biological Sciences at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in John Janovy Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Hanelt & Janovy, Life Cycle of a Horsehair Worm, Gordius robustus (Nematomorpha: Gordoidea) Journal of Parasitology (1999) 85. Copyright 1999, American Society of Parasitologists. Used by permission.

RESEARCH NOTES 139

J. Parasitol., 85(1), 1999 p. 139-141 @ American Society of Parasitologists 1999

The Life Cycle of a Horsehair Worm, Gordius robustus (Nematomorpha: Gordioidea)

Ben Hanelt and John Janovy, Jr., School of Biological Sciences, University of Nebraska-lincoln, Lincoln, Nebraska 68588-0118

ABSTRACf: Aspects of the life cycle of the nematomorph Gordius ro­ Nematomorphs are a poorly studied phylum of pseudocoe­ bustus were investigated. Gordius robustus larvae fed to Tenebrio mol­ lomates. As adults they are free living, but their ontogeny is itor (Coleoptera: Tenebrionidae) readily penetrated and subsequently completed as obligate parasites. Despite their cosmopolitan dis­ encysted in the posterior portion of the midgut wall. Parasite develop­ tribution, the details of the nematomorph life cycle remain ment was then arrested in each infected beetle. Upon feeding these cysts poorly understood (Chandler, 1985; Poinar, 1991; Schmidt­ to laboratory-reared Gryllus firmus. worm larvae developed to adults in the cricket hemocoel. In an additional experiment, G. robustus larvae Rhaesa, 1997). Adults of the class Gordioidea, also commonly fed to G. firmus did not develop to adults. These findings are in contrast known as hair worms or gordian worms, are usually found to other studies that found direct infection to be an alternative mode of emerging from coleopteran or orthopteran insects, although a infection. This experiment is the first employing a laboratory-main­ variety of other animals are known to serve as definitive hosts tained stock of hosts to rear nematomorph worms. (for a compiled list see Cappucci [1976]). Hanelt & Janovy, Life Cycle of a Horsehair Worm, Gordius robustus (Nematomorpha: Gordoidea) Journal of Parasitology (1999) 85. Copyright 1999, American Society of Parasitologists. Used by permission.

140 THE JOURNAL OF PARASITOLOGY, VOL. 85, NO.1, FEBRUARY 1999

Two strategies have been proposed to explain how larvae, TABLE I. Gordius robustus encysted larvae and adults found in Tenebrio emerging from eggs deposited in fresh water, reach their defin­ molitor and Gryllus firmus exposed to larvae and encysted larvae. itive hosts: (I) direct infection with larvae or free encysted (in the environment) larvae; and (2) indirect infection by larvae Exposed to M. molitor* G. firmust encysted within an intermediate host that is consumed by a Larvae 18/27 0/7 definitive host. Experimentation with, and observation of, mem­ Encysted larvae Not done 4/7 bers of various species of nematomorphs over the last 150 yr Controls 0120 0/20:1: have not been able to resolve conclusively the method by which * Number of cysts/total. the aquatic free-living larvae are transmitted to their terrestrial t Number of adults/total. definitive hosts. :j: Number of adults and cysts/total. May (1919) injected orally and systemically larvae of the genus Gordius into grasshoppers to test for direct infection. Of 46 individuals exposed, 11 harbored preadult stages of the par­ most of the larvae were freed, the egg sack was removed. Lar­ asite. May (1919) concluded that gordians are not required to vae were easily concentrated by swirling the water, herein de­ change hosts during their life cycle. However, inadequately fined as infested water, containing 50-100 larvae per drop. timed parallel controls place uncertainty on whether the hosts Tenebrio molitor L. colonies were maintained as described used were not naturally infected. Thorne (1940) conducted a by Clopton and Janovy (1993). Twenty T. molitor larvae were similar experiment but failed to include controls altogether. isolated in 6-L plastic containers on a bedding of bran, covered More recently, direct infections were successful in 3 of 12 man­ with paper towels moistened every 2-3 days. Newly emerged tids exposed to Chordodes japonensis larvae (Inoue, 1962). Do­ adult beetles were starved for 48 hr to encourage uptake of rier (1930) reported the encystsment of larvae in the aquatic liquid. To facilitate infection, individuals were confined to "bug environment. Excystation would occur when placed in contact beds," consisting of microscope slides, the width of which was with host intestinal fluids, thus allowing for infection via gut wrapped in a single layer of 19-mm laboratory tape, adhesive wall penetration (Dorier, 1930, 1935). The production of free side up. Tenebrio molitor individuals were stuck ventral side cysts has not been documented since. up to the tape on this slide and covered by a piece of 17-mm Infection via intermediate hosts was first postulated by Meis­ laboratory tape. Incapacitated individuals were placed under a sner (1856) after noting nematomorph larvae entering and en­ steromicroscope. Using a fine glass pipette, a drop of infested cysting in Ephemeroptera larvae. This observation led Meissner water was placed on the mouthparts. Only those individuals that (1865) to suggest that aquatic insects serve as intermediate were observed to take in all of the water were considered ex­ hosts. Inoue (1962) showed that 21 of 26 mantids became in­ posed; others were discarded. Individuals serving as controls fected when fed Cloeon dipterum (Insecta: Ephemeroptera) lar­ were not infected and were kept in identical conditions as the vae containing cysts of C. japonensis. This led Inoue (1962) to treated group. The degree of infection was determined by re­ conclude that indirect infection through cyst-containing aquatic moving, dissecting, and viewing the whole gut 14-30 days post­ insect larvae is more important than the direct ingestion of ne­ exposure (dpe), mounted in a drop of water. matomorph larvae from the water. Gryllus firmus colonies were maintained in 25.5-L aquaria, The objective of the present preliminary investigation was to lined with paper towels, and containing half of an egg carton. elucidate the life cycle of a nematomorph, Gordius robustus Individuals were reared by feeding ad libitum on water and Leidy, 1851, which is widely distributed in the United States solid commercial cat food, ground to a fine powder. Adults, (Chandler, 1985). Experiments were performed to test the pos­ ultimate, and penultimate instar individuals were used in infec­ sibilities of direct and indirect infection of G. robustus as the tion experiments. Individuals were starved for 24 hr to enhance definitive host. uptake of liquid. To test the direct life-cycle strategy, G. firmus Individuals of G. robustus were collected from Las Huertas individuals were seized by the back legs and fed infested water. creek (35°16/20"N, 106°24/55/'W), located on the northern slope Again, only individuals that were seen to take in all of the water of the Sandia Mountains, Bernallio County, New Mexico. At were considered exposed; others were discarded. Individuals this site, the natural host of G. robustus was Anabrus simplex serving as controls were not infected and were kept in identical Haldeman, 1852 (Mormon cricket; B. Hanelt, pers. obs.). Worm conditions as the treated group. Prior to dissection, each indi­ pairs found copulating were isolated; remaining worms were vidual was observed for signs of pathology. Infection was as­ paired randomly and placed in 1-L plastic containers in well sessed by dissection of crickets 90-100 dpe. water with aeration. Egg strings were collected from each mated To test the indirect mode of infection, G. firmus individuals pair and briefly rinsed in a 1:250 Clorox@ bleach: well-water were placed into 4.5-cm covered petri dishes containing the solution. A 60-ml glass jar, rinsed previously with the bleach dissected fore-, middle, and hindgut, extracted from T. molitor solution, was used to keep a stock of G. robustus larvae stored 28-36 dpe to G. robustus larvae. Only those crickets that com­ in well water. All experiments were conducted with eggs pro­ pletely consumed the beetle gut were considered exposed; oth­ duced from 1 mating pair. ers were discarded. Exposed crickets were kept in 1-L plastic Pieces of egg strings (2-4 mm in length), in which eggs had containers with the same conditions as the colonies. To assess matured, were placed into depression slides with 1 or 2 drops infection, crickets were dissected between 90 and 100 dpe. of tap water. Egg maturity was judged using the color of the Worms were enumerated, sexed, and measured. egg strings; strings became darker as the larvae developed (Val­ Cysts were found in 18 of the 27 T. molitor individuals ex­ vassori et aI., 1988). The sack was teased apart using dissecting posed to G. robustus (Table I). Four of the 7 cyst-exposed G. needles, causing larvae to fall free from the egg string. Once firmus were found to contain G. robustus worms. The 4 hosts Hanelt & Janovy, Life Cycle of a Horsehair Worm, Gordius robustus (Nematomorpha: Gordoidea) Journal of Parasitology (1999) 85. Copyright 1999, American Society of Parasitologists. Used by permission.

RESEARCH NOTES 141

TABLE II. Adult Gordius robustus recovered from Gryllus fimlUs ex­ This study has been the first to rear adult nematomorphs in posed to encysted larvae. laboratory-maintained stocks of intermediate and definitive hosts. In the future, this domestication will hopefully lead to­ Number of worms Length of worms* Individual/ ward a fuller understanding of the life cycle of this largely sex Males Females Males Females unstudied group. We thank A. J. Zera for providing us with laboratory-reared 1. Female 3 3 168 228.7 G. firmus and S. V. Brant for critically reading this manuscript. 2. Female 0 I 230 We also thank 2 anonymous reviewers whose suggestions im­ 3. Female 0 I 154 4. Male I 2 174 209.5 proved this paper, and Cedar Point Biological Station where the early stages of this research was conducted. * Calculated as mean, in mm. LITERATURE CITED BARETH, c. 1974. Presence de kystes et de larves de Gordiaces chez plusieurs especes de Campodes cavernicoles (Diploures, Campod­ contained a total of II worms. The length of worms ranged eides). Annales de Speleologie 29: 657-662. from 157 to 230 mm (Table II). Males were generally smaller BLAIR, D. 1983. Larval horsehair worms (Nematomorpha) from the tis­ than females. No control animals contained cysts or worms. sue of native freshwater fish in New Zealand. New Zealand Journal Although worms removed from hosts looked mature, none mat­ of Zoology 10: 341-344. ed. Development of the reproductive systems of the worms was CAPPUCCI, D. T. 1976. The biology of Gordius robustus Leidy with a host list and summary of the public health importance of the Gor­ not assessed. dioidea. Ph.D. Dissertation. University of California, San Francis­ Larvae stored in tap water at 4 C remained viable for at least co, San Francisco, California, 240 p. 5 mo (data not shown). One batch of eggs produced by a single CHANDLER, C. M. 1985. Horsehair worms (Nematomorpha, Gordioidea) mating pair of adult G. robustus consistently produced cysts in from Tennessee, with a review of taxonomy and distribution in the United States. Journal of the Tennessee Academy of Sciences 60: T. molitor over this period of time. Behavior of both' infected 59-62. and uninfected crickets seemed identical. Each cricket resisted CLOPTON, R. E., AND J. JANOVY, JR. 1993. Developmental niche structure capture; none was lethargic or otherwise suffering from obvious in the gregarine assemblages parasitizing Tenebrio molitor. Journal pathology. All infected crickets lacked gonads and fat bodies. of Parasitology 79: 701-709. The necessity of an encysted stage in the hairworm life cycle DORIER, A. 1930. Classe des Gordiaces. In Traite de zoologie, vol. 4, P. P. Grasse (ed.). Masson, Paris, France, p. 1201-1222. has been a point of confusion. Muller (1920) contended that ---. 1935. Sur Ie passage a la vie laterte des larves de Gordiaces. encysted larvae occur because they are "verirrt," lost, or Comptes Rendus de l'Academie des Sciences, Paris 200: 492-494. strayed. More recently, Pennack (1989) speculated that larval INOUE, I. 1960. Studies on the life history of Chordodes japonensis, a encystment within a host is indicative of an abnormal host, species of Gordiacea II. On the manner of entry into aquatic insect­ larvae of Chordodes larvae. Annotationes Zoologicae Japonenses although further development is possible if ingested by the cor­ 33: 132-141. rect host. These statements, along with the results of Inoue ---. 1962. Studies on the life history of Chordodes japonensis, a (1962), suggest that intermediate hosts are possible in the hair species of Gordiacea III. The modes of infection. Annotationes worm life history but not required. In the present preliminary Zoologicae Japonenses 35: 12-19. investigation, we found that G. robustus larvae did not infect MAY, H. G. 1919. Contributions to the life histories of Gordius robustus (Leidy) and Paragordius varius (Leidy). Il1inois Biological Mono­ G. firmus (direct), whereas encysted G. robustus larvae did (in­ graphs 5: 1-119. direct). This result indicates that the encysted larvae, thus the MEISSNER, G. 1856. Beitrage zur Anatomie und Physiologie der Gor­ intermediate hosts, are required for successful infection of G. diaceen. Zeitschrift fUr wissentschaftliche Zoologie 7: 1-144. firmus. MOLLER, G. W. 1920. Beobachtung an Gordius. Zoologisher Anzeiger 51: 225-229. The likelihood of a terrestrial beetle, such as T. molitor, com­ PENNACK, R. W. 1989. Fresh-water invertebrates of the United States. ing into contact with aquatic nematomorph larvae is unknown, Protozoa to Mollusca, 3rd ed. John Wiley and Sons, Inc., New especially because the larvae are not agile swimmers and sink York, New York, 628 p. in water (B. Hanelt, pers. obs.). Thus, it is possible that ne­ POINAR, G. O. 1991. Hairworm (Nematomorpha: Gordioidea) parasites of New Zealand wetas (Orthoptera: Stenopelmatidae). Canadian matomorphs are extreme generalists at the intermediate host Journal of Zoology 69: 1592-1599. level and have the capacity to enter and encyst in a variety of ---, AND J. J. DOELMAN. 1974. A reexamination of Neochordodes aquatic hosts, some of which might come into contact with the occidentalis (Montg.) comb. n. (Chordodidae: Gordioidea): Larval definitive host species. This scenario is plausible due to the penetration and defense reaction in Culex pipens. Journal of Para­ sitology 60: 327-335. recorded findings of nematomorph cysts in a wide variety of SAWYER, R. T. 1971. Erpobdellid leeches as a new host for the nema­ hosts ranging from arthropods (e.g., Bareth, 1974) and annelids tomorph, Gordius sp. Journal of Parasitology 52: 258. (e.g., Sawyer, 1971) to vertebrates (e.g., Blair, 1983). Therefore, SCHMIDT-RHAESA, A. 1997. Freshwater fauna of central Europe, volume although a tenebrionid beetle can serve as an intermediate host, 4/4. Gustav Fisher Verlag, Stuttgart, Germany, 128 p. it might not do so in nature. Alternatively, nematomorph larvae THORNE, G. 1940. The hairworm, Gordius robustus Leidy, as a parasite of the mormon cricket, Anabrus simplex Haldeman. Journal of the are known to enter readily and encyst in aquatic insect larvae Washington Academy of Sciences 30: 219-231. (Meissner, 1856; Inoue, 1960; White, 1969; Poinar and Doel­ VALVASSORI, R., G. SCARI, M. DE EGUILEOR, L. 01 LERNIA, P. MAGNETTI, man, 1974). Although not established, nematomorph cysts AND G. MELONE. 1988. Gordius villoti (Nematomorpha) life cycle could survive the metamorphosis of aquatic larvae, which in relation with caddis fly larvae. Bollettina di Zoologia 55: 269­ 278. would then serve as vehicles to span the gap between the aquat­ WHITE, D. A. 1969. The infection of immature aquatic insects by larval ic and terrestrial environments. Paragordius (Nematomorpha). Great Basin Naturalist 29: 44.