262 Journal of Nematology, Volume 13, No. 3, July 1981 13. Petersen, J. J. 1973. Role of mermithid nema- quito larvae. Mosq. News 32:312-316. todes in biological control of mosquitoes. Exp. 22. Petersen, J. J., and O. R. Willis. 1974. Ex- Parasitol. 33:239-247. perimental release of a mermithid to 14. Petersen, J. J. 1976. Comparative biology of control Anopheles mosquitoes in Louisiana. Mosq. the Wyoming and Louisiana populations of Reesi- News 34:316-319. mermis nielseni, parasitic nematode of mosquitoes. 23. Petersen, J. J., and O. R. Willis. 1974. Dixi- J. Nematol. 8:273-275. merinis peterseni (Nematoda: Mermithidae): A po- 15. Petersen, J. J. 1979. pH as a factor in para- tential biocontrol agent of Anopheles mosquito sitism of mosquito larvae by the mermithid larvae. J. Invert. Pathol. 24:20-23. Romanomermis culicivorax. J. Nematol. 11:I05-106. 24. Petersen, J. J., and O. R. Willis. 1975. Es- 16. Petersen, J. J. 1981. Observations on the biol- tablishnrent and recycling of a mermithid nematode ogy of Octomyomermis musprani, a nematode para- for the control of mosquito larvae. Mosq. News 35: site of mosquitoes. J. Invert. Pathol., in press. 526-532. 17. Petersen, J. J., and H. C. Chapman. 1979. 25. Platzer, E. G., and B. J. Brown. 1976. Physi- Checklist of mosquito species tested against the ological ecology of Reesimermis nielseni. Proc. Int. nematode parasite Romanomermis culicivorax. J. Colloq. Invert. Pathol., Kingston, Canada, pp. 263- Med. Entomol. 15:408-471. 267. 18. Petersen, J. J., H. C. Chapman, O. R. Willis, 26. Platzer, E. G., and J. E. Eby. 1980. Mer- and T. Fukuda. 1978. Release of Romanomermis mithid in mosquito control: persistence culicivorax for the control of Anopheles albimanus in small experimental ponds. Proc. Calif. Mosq. in E1 Salvador. II. Application of the nematode. Vector Cont. Assoc. 48:40-41. Am. J. Trop. Med. Hyg. 27:1268-1273. 27. Platzer, E. G., and L. L. MacKenzie-Graham. 19. Petersen, J. J., c. D. Steehnan, and O. R. 1978. Predators of Romanomermis culicivorax. Proc. Willis. 1973. Field of two species of Calif. Mosq. Vector Cont. Assoc. 46:93 (Abstr.). Louisiana rice field mosquitoes by a mermithid 28. Platzer, E. G., and L. L. MacKenzie-Graham. nematode. Mosq. News 33:573-575. 1980. Cyclops vernalis as a predator of the prepara- 20. Petersen, J. J., and O. R. Willis. 1970. Some sitic stages of Romanomermis culicivorax. Mosq. factors affecting parasitism by mermithid nematodes News 40:252-257. in southern house mosquito larvae. J. Econ. 29. l'oinar, G. O., Jr. 1975. Entomogenous Nema- Entomol. 63:175-178. lodes. Leiden: E. J. Brill. 21. Petersen, J. J., and O. R. Willis. 1972. Re- 30. l'oinar, G. O., Jr. 1979. Nematodes for Bio- suits of preliminary field application of Reesimermis logical Control of Insects. Boca Raton, Florida: nielseni (Mermithidae: Nematoda) to control mos- CRC Press.

Mermithid Parasites of Agricultural Pest Insects 1 W. R. Nickl&

Plant and insect nematologists generally mithids, called preparasites, in soil samples agree that nematodes are well adapted to from agricultural fields. They are about 1 the soil environment. And since over 90% nnn in length, narrow, and resemble long of all agricultural pest insects spend at least Tylenchus sp. larvae in their shape and a part of their lives in the soil, a situation moving habits. After infecting their host, exists which favors an encounter between the preparasites continue their development the two organisms. When the encounter in- through the several larval stages and egress volves an insect susceptible to a mermithid from the host insect as fully grown post- nematode, a parasitic relationship may en- parasites which no longer feed. Egress from sue. Additionally, infective stages of several the host insect causes a large hole from species of mermithids climb low-growing which the insect loses its essential fluids and plants to infect susceptible host insects dies. The postparasites, 2-25 cm in length, which feed on the leaves or in stems. Nema- re-enter the soil and move to a depth of tologists can find the infective stage of mer- 15-50 cm, often well beneath the plow layer where the soil is more sterile and free Received for publication 12 December 1980. from fungal parasites and predators. Here aSymposium paper presented at the annual meeting" of the Society of Nematologists, New Orleans, Loulsiana, Au- they molt to adults and mate. In the fall, gust 1980. they often form balls (Fig. 1) consisting of 2Nematology Laboratory, Plant Protection Institute. USDA SEA AR, BARC.West, Beltsville, MD 20705. a female and one or more males. The eggs Mermithids of Agricultural Insects: Nickle 263

Figs. 1-11. Mermithid parasites of agricultural pest insects. 1) Agamermis decaudata females ball in soil from Virginia. 2) Grasshopper from Montana with . 3) Long-horned grasshopper from Maryland with Agamermis decaudata 4) Clover leafhopper from Maryland with Agamerrnis decaudata 5) Japanese beetle grub from Vermont with a Psamrnomerrnis sp. 6) Tent caterpillar from Virginia with a Hexamermis sp. 7) Gypsy moth mermithid of the genus Hexamermis from Europe. 8) Mohagany shoot borer from Costa Rica with a Hexamerrnis sp. 9) Culicoides biting fly from New York with a Heleido- rnermis sp. 10) Armyworm with Hexamermis mermithid from Nicaragua. 11) Ant from Austria with met- mithid (courtesy of H. Kaiser). are sometimes deposited within the ball. In sometimes adult host insects. At least six the spring, when soil temperatures increase variations of this life cycle, have been de- and rain water is available, the mermithid scribed; some are much more complicated. eggs hatch and tile preparasites move to the Observations on penetration of prepara- surface and penetrate the larval, pupal, and sitic stage mermithids into larval army 264 Journal of Nematology, Volume 13, No. , July 1981 worms and root worms show that esophageal sect, extending from the thoracic region to secretions are used to attach the nematode the preultimate abdominal segment. Sixty to the host while other secretions, perhaps percent of the grubs collected from sandy chitinase, along with rasping tooth action soil from the town green at Brattleboro, facilitate penetration. Infection usually Vermont, were infected by this mermithid. culminates in host death. High percentages Poinar and Gyrisco (14) reported that up to of parasitism of certain agricultural pest in- 33% of the alfalfa weevils in parts of New sects by nematodes have been reported (9, York State were parasitized by the mer- 12,13,18). These will be discussed under the mithid Hexamermis arvalis. Cuthbert (3) orders of insects: Orthoptera, Coleoptera, reported that 50-100% of the banded Lepidoptera, Diptera, and other miscel- cucumber beetle larvae collected from fields laneous groups. in Charleston, South Carolina, were para- sitized by a nematode named Filipjevi- ORTHOPTERA mermis leipsandra by Poinar and Welch (15). Most of the insects parasitized by this Much of the early work in mermithid nematode died before they pupated, which parasites of agricnltural insects concerned is the normal situation. Of the 219 insects Mermis nigrescens and Agamermis decau- studied, 86% were last-instar larvae when data on grasshoppers (2,4). In the spring, the mermithids emerged, 6% were pre- after a rain or when the dew is heavy, M. pupae, 7% were pupae, and 1% were nigrescens females, which are about 8 cm in adults. Infected larvae became slightly length, move out of the soil and crawl onto swollen and assumed a characteristic light the existing vegetation to lay their eggs. The tan color. They were sluggish, their move- eggs may then be ingested by grasshoppers ment was uncoordinated, and well-devel- feeding on the vegetation. Ingested eggs oped mermithids could be seen through the batch within the gut of the insect and the body wall. preparasites penetrate into the body cavity In cooperative research with Dr. where they enlarge (Fig. 2). Farmers and R. Schroder, Beneficial Insect Introduction home gardeners occasionally send in these Laboratory, Beltsville Agricultural Re- grasshopper mermithids which they find on search Center, and Dr. J. Krysan, Northern their vegetables for identification along Grain Insects Research Laboratory, Brook- with a request for control measures for these ings, South Dakota, we are studying a nematodes. It is contended that mermithids South American mermithid parasite of corn are important in the control of grasshopper root worms. This is the first caged field re- populations in the eastern part of the lease of an exotic nematode. Research is United States (J. Christie and G. Thorne, also being done at Beltsville, Maryland, on personal communication). At Beltsville, A. a Hexamermis from Colorado potato beetle decaudata also was found to parasitize new sent from Austria by Dr. H. Kaiser, Uni- hosts in nature, such as long-horned grass- versity of Graz. It is part of a Small Farms hoppers (Fig. 3), crickets, wolf spiders, and Research Project at BARC. We are running leafhoppers (Fig. 4) (Nickle, unpublished some studies on ladybugs and other bene- data). ficial Coleopterans and have met with APHIS and have set up requirements for COLEOPTERA a field release of this introduced insect para- Mermithids are parasitic on leaf- and sitic nematode. root-feeding beetles. Sixty percent of the LEPIDOPTERA June beetles in parts of the USSR are in- fected by Psammomermis spp. (16). Sixty Mermithids can be found in caterpillars percent of the .Japanese beetle grubs (Fig. and other larval lepidopterans. They were 5) from lawns in the northeastern United found by Kaburaki and Imamura (6) in states were found by Klein et al. (8) to be 76% of the rice borers, Chilo simplex, in parasitized by a similar mermithid nema- Japan. We found a Hexamermis sp. from tode. This mermithid is about 20 cm in tent caterpillars (Fig. 6) on Prunus from length and can be seen coiled inside the in- New Jersey to Virginia. Artyukhovsky (1) Mermithids of Agricultural Insects: Nickle 265 reported that up to 60% of the gypsy moth gynes are parasite-induced forms that are caterpillars were parasitized by a Hexa- shaped halfway between workers and mated mermis sp. south of Moscow. We period- female ants. Mermithostratiotes are female ically receive living specimens of this nema- forms with heads shaped like those of tode from the USDA European Parasite soldier ants. Mermithogynes and mermither- Laboratory but have not established a gates have swollen abdomens, whereas their permanent culture as yet. We now have heads and thoraces remain normal or are re- living postparasites (Fig. 7) of gypsy moth dttced in size. mermithids from Europe. Nickle (10) in- fected the fall armyworm with a Hexa- CONCLUSIONS rnermis mermithid nematode (Fig. 10). Plant nematologists would be interested in Mermithid nematodes have the potential knowing that the infective stage, which was to suppress popuIations of agricultural pest 1 mm in length, grew to a postparasitic ittsects including grasshoppers, several beet- nematode 20 cm in length (Fig. 11) in only les and caterpillars, and some leafhoppers, 20 days inside the armyworm caterpillar. ants, anti other insect groups. The moist soil Nickle and Grijpma (11) found up to 25% habitat is ideal for the life cycles of mer- of the shoot borers, Hypsipyla grandella mithid nematodes. The effect on insects (Zeller) (Pyralidae), (Fig. 8) were infected parasitized by mermithids is usually death. by Hexamermis albicans at the end of the Most agrictdtural pest insects spend some wet season in Costa Rica. They list 70 other time in the soil where they would be sus- species of Lepidoptera wltich are para- ceptible to parasitism by mermithids when sitized by mermithids. temperature and moisture are favorable. Infective stage mermithids resemble plant DIPTERA parasitic nematodes in appearance and be- havior. Mosquitoes and black flies are only Mass rearing and release of mermithids marginally important in agriculture and are with potential as biocontrol agents should dealt with elsewhere in this symposium. continue. Importation of exotic mermithids Some Culicoides spp., which transmit blue from abroad should also be undertaken for tongue and other virus diseases of cattle, future releases on agricultural pests. sheep, and deer, are parasitized by mer- mithids in the genus Heleidomermis (Fig. LITERATURE CITED 9). Mermithids also parasitize tabanids. 1. Artyukhovsky, A. K. 1953. Infection of Por- thetria dispar caterpillars with the nematode Hexa- OTHER INSECT ORDERS mermis alhicans (Siebold, 1848) Steiner, 1924. Pp. 31-33 in K. I. Skriabin 75th Anniv. Comm. Vol. Kaburaki and Imamura (7) reported Contributions to Helminthology. that the mermithid nematode, Agamermis 2. Cobb, N. A., G. Steiner, and J. R. Christie, unha, played an important role in the 1923. Agamermis decaodata Cobb, Steiner, and Christie; a nematode parasite of grasshoppers and natural control of certain rice leafhoppers other insects. J. Agric. Res. 23:921-926. in Japan. Parasitism and resultant death 3. Cuthbert, F. P., Jr. 1968. Bionomics of a occurred in 70% of the entire population mermithid (Nematoda) parasite of soil-inhahiting of Sogota [urcifera and 41% of the total larvae of certain Chrysomelids (Coleoptera). J, Invertebr. Path. 12:283-287. popultion of Nilaparvata oryzae. In Belts- 4. Glascr, R. W., and A. M. Wilcox. 1918. On viIIe, the clover leafhopper was a good host the occurrence of a Mermis epidemic amongst grass- of our local Agamermis decaudata follow- hoppers. Psyche 25:12-15. ing early spring rains (personal observa- 5. Gouht, ~V. 1747. An Account of English Ants, tions). London. 6. Kaburaki, T,, and S, hnamura. 1932. A new Ants are often parasitized by mermithids mermithid-wnrm parasitic in the rice borer, with (Fig. l l). ]n 1747, Gould (5) noted mer- notes on its life history and habits. Prec. Impcr. mithids parasitizing the ants, Lasius flavus, Acad. 8:109-112. in England. Wheeler (17) described dis- 7. Kaburaki, T., and S. hnamura. 1932. Mer- mithid-worm parasitic in leafhoppers, with notes on tinct morphological alterations induced in its life history and habits. Proc, Imper. Acad. 8: ants parasitized by mermithids. Mermitho- 139-141. 266 Journal of Nematology, Volume 13, No. 3, july 1981

8. Klein, M. G., W. R. Nickle. P. R. Benedict, logical control of insects. Boca Raton, Florida: and D. M. Dunbar. 1976. Psammomermis sp. C.R.C. Press. (Nematoda: Mermithidae): A new nematode para- 14. Poinar, G. O., Jr., and G. G. Gyrisco. 1962. site of the Japanese beetle, Popillia japonica Studies on the bionomics of Hexamermis arvalis (Coleoptera: Scarabaeidae). Proc. Helm. Soc. Wash. Poinar & Gyrisco, a mermitbid parasite of the 43:235-236. alfalfa weevil, Hypera postica (Gyllenhal). J. Insect 9. Nickle, W. R. 1974. Nematode infections. Pp. Path. 4:469-483. 327-376 in G. E. Cantwe]l, ed. Insect diseases. New 15. I'oinar, G, 0., Jr., and H. E, Welch. 1968. A York: Marcel Dekker. new nematode, Filipjevimermis leipsandra sp. n. 10. Nickle, W. R. 1978. On the biology and life (Mermithidae), parasitic in Chyrsomelid larvae history of some terrestrial mermithids parasitic on (Coleoptera). J. Invert. Pathol. 12:259-262. agricultural pest insects. J. Nematol. 10:295 (Abstr.). 16. Polozhentsev, P. A. 1952. New Mermithidae 11. Nickle, W. R., and P. Grijpma, 1974. Studies of sandy soil of pine forests. Trudy Helmintb. Lab. on the shootborer, Hypsipyla grandella (Zeller) 6:376-~82. (Lep.. Pyralidae) XXV. Hexamermis albicans (Sie- 17. Wheeler, W. M. 1928. Mermis parasitism and bold) (Nematoda: Mermithidae) a parasite of the intercastes among ants. J. Exp. Zool. 50:165-237. larva. Turrialba 24:222-226. 18. Welch, H. E. 1963. Nematode infections. Pp. 12. Poinar, G. O., Jr. 1975. Entomogenous 363-392 in E. A, Steinhaus, ed. Insect pathology. nematodes. Leiden: E. J. Brill. New York: Academic Press. 13. Poinar, G. O., Jr. 1979. Nematodes for hip-

Mermithid Nematodes: Physiological Relationships with their Insect Hosts 1 Roger Gordon ~ Abstract: This paper assesses our state of knowledge of physiological processes involved in the relationships between insects and their mermithid nematode parasites. Three major components of the host-parasite relationship(s) are reviewed: effects of mermithids on host physiology, effects of host physiology on mermithids, and the physiology of the nematodes themselves. Mermithids induce an array of changes in host physiology, and the effects on host metabolism and endocri- nology are discussed at some length. Few studies have been done to ascertain the effects of the host on the parasites from a physiological standpoint. Whereas host immunity mechanisms against mermithids have been described at the ultrastructural level, the physiological basis of such responses is not known. Mermithids are atypical nematodes, both structurally and physio- logically. In the absence of a functional gut, nutrients are absorbed across the outer cuticle and stored in a trophosome. The transcuticular mode of feeding, storage within the trophosome, and metabolism of storage products are discussed. The usefulness of physiological information toward expediting in vitro culture of these nematodes is discussed, and problems that need to be ad- dressed are defined. Key words: cuticle, fat body, Filipjevimermis leipsandra, Gastromermis boophthorae, hemolytnph, immunity, Mermis nigrescens, mermithid nematode, Neomesomermis flumenalis, Romanomermis culicivorax, trophosome.

Mermithid nematodes (Enoplida: Mer- sterile. The potential of mermithids for mithidae) have considerable potential for insect biocontrol, however, has yet to be biocontrol of insect pests. The insect host realized. Only one species of mermithid, the invariably dies when the juvenile nematode mosquito parasite Romanomerrnis culici- completes its parasitic development and vorax, has been mass cultivated on the scale exits from the host's hemocoel (the para- needed to permit field trials and for this an site's microenvironment). When adult fe- in vivo procedure was used (29). Several male insects are infected, they are rendered authorities (28,46) have advocated the es- tablishment of in vitro cultivation pro- Received for publication 9 February 1981. cedures because they are potentially 1Symposium paper presented at the annual meeting of the Society of Nematologists, New Orleans, Louisiana, Au- cheaper, more efficient, and easier to main- gust 1980. tain than in vivo methods. However, at- 2Department of Biology, Memorial University of New- foundland, St. John's, Newfoundland, Canada AIB 3X9. tempts to culture mermithids in vitro (8) Continuing financial support from the Natural Sciences /lave met with limited success. and Engineering Research Council of Canada (Grant No. A6679) is gratefully acknowledged. The paucity of information about the