University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln 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] Follow this and additional works at: https://digitalcommons.unl.edu/bioscijanovy Part of the Parasitology Commons 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.