270 Journal of Nematology, Volume 12, No. 4, October 1980 terial parasite of a plant : morphology and Pasteuria-Blastobacter group. Can. J. Microbiol. 19: ultrastrueture. J. Bacteriol. 129:1091-1101. 609-614. 26. Sayre, R. M., W. P. Wergin, and R. E. Davis. 30. Thorne, G. 1940. Duboscqia penetrans n. sp. 1977. Occurrence of Moina rectirostris (Cladocera: (Sporozoa, Microsporidia, Nosematidae), a parasite Daphnidae) of a plant morphologically similar to of the nematode Pratylenchus pratensis (de Man) Pasteuria ramosa (Metchnikoff, 1888). Can. J. Filipjev. Proc. Hehn. Soc. Wash. 7:52-53. Microbiol. 23:1573-1579. 31. Walker. J. T. 1969. Pratylenchus penetrans 27. Shepherd, A. M., S. A. Clark, and A. Kemp- (Cobb) populations as influenced by microorganisms ton. 1973. An intracellular microorganism associated and soil amendments. J. Nematol. 1:260-264. with tissues of Heterodera spp. Nematologica 19: 32. Williams, J. R. 1960. Studies on the nema- 31-34. tode soil fauna of sugarcane fields in Mauritius. 28. Slack, J. M., and M. A. Gerencser. 1975. Nematologica 5:37-42. Actinomyces, filamentous bacteria; biology and 33. Williams, J. R. 1967. Observations on para- pathogenicity. Burgess Publishing Co., Minneapolis. sitic protozoa in plant-parasitic and free-living nem- p. 175. atodes. Nematologica 13:336-342. '29. Staley, J. T. 1973. Budding bacteria of the

Biocontroh The Potential of Entomophilic in Insect Management 1 John M. Webster 2 Abstract: A review of the development of entomophilic nematology and a commentary on the potential of entomophilic nematodes in controlling insect pests. The paper considers some of the major contributions to our knowledge of entomophilic nematology; factors involved in insect pest management and how they are applicable to the use of nematodes; nematodes which are most promising as biological control agents; and problems to be solved to facilitate the use of entomophilic nematodes in insect management. Key Words: Mermis nigrescens, Neoaplectana spp., Romanomermis culicivorax, Deladenus siricidicola, Tetradonema plicans.

"A modern endeavour is to bring insect realized. Why? In the following discussion pests under natural control ..... The I will give some of the reasons. 'natural control' of insects will be most effective if all possible agencies and fac- MILEPOSTS tors are utilized; among these agencies nemas are by no means negligible." Mermis nigrescens, though atypical of the family, is often considered the type or- This is a quotation from Nathan Cobb ganism for entomophilic nematology and (12) in the 1927 USDA Yearbook of Agri- was described by Dujardin in France 137 culture. In recent years, pest management years ago (16). About 20 years later, Sir philosophy has developed in ways that John Lubbock, in Edinburgh (34), pro- avoid harm to useful organisms. As nema- vided biological and taxonomic informa- todes that kill pest insects are usually harm- tion on Sphaerularia bombi that widened less to other organisms, they have enormous contemporary perspectives on the nature of potential for use in place of chemical pesti- nematode-insect associations. Numerous cides in pest management systems. Never- publications in entomophilic nematology theless, more than 50 years after Cobb's followed, especially in Germany, and this statement, this potential has yet to be fully was crowned in the early part of the 20th century by a detailed taxonomic account of Received for publication18 February 1980. the mermithids by Hagmeier (27) of the 1Symposium paper presented at the annual meeting of University of Heidelberg. Cobb (10) entered the Society of Nematologists, Salt Lake City, Utah, U.S.A., 23-26 July 1979. tile arena in 1920 with descriptions of sev- 2Pestology Centre, Department of Biological Sciences, eral new species of entomophilic nematodes Simon Fraser University,Burnaby, Vancouver, Canada. VSA lS6. and followed by his famous observations on I thank Dr. B. P. Beirne of Simon Fraser University the biology and of mermithids and Dr. J. J. Petersen of the United States Department of Agriculture for comments on the manuscript. (I 1,13). During the first half of the 20th cen- Entomophilic Nematodes: Webster 271 tury Cobb in the United States, Filipjev in of research stepped Rachael Carson, whose Russia, Steiner in Germany, and Bovien in book (8) stimulated major shifts in the Denmark made significant contributions to agricultural and social philosophies of the our understanding of the taxonomy of en- industrialized world. Since that time we tomophilic nematodes, and Tom Goodey's have witnessed a plethora of publications in presentation (22) to the Royal Society in entomophilic nematology and this time, 1930 on the biology and taxonomy of the nematologists have focused more on the use tylenchid Tylenchinema oscinellae, a para- of nematodes in insect control rather than site of the flit fly, was, and still is, a fine ex- on their taxonomy. ample of detailed biological observation. Many claim that tylenchids are possible Superimposed on these were Oldham's biological control agents (37,45). However, perspicacious comments in his paper "Hel- the only major success has been that of minths in the biological control of insect Bedding (1,2,4,5), with the Commonwealth pests" published by the former Imperial Scientific and Industrial Research Organiza- Bureau of Agricultural Parasitology (39). tion in Australia, using Deladenus, a Thereafter, interest in the subject waned for tylenchid parasite of the Sirex woodwasp. 20 years, except for occasional curiosity re- The mermithid parasites of insects have cordings such as that of Muspratt (35), who emerged as the most favoured nematological described mermithids in tree-hole breeding tool for insect control, and significant ad- Culicidae. vances have been made in all aspects of our Despite the mental perambulations of knowledge of this group--on their taxonomy Cobb in 1927, and the enthusiasm and suc- by Rubtsov (48,57) and Welch (55,57), on cesses of the 1930s, little progress was made their biology and ecology by Petersen (40, toward the application of entomophilic 43), and on the physiological and biochem- nematodes in the control of pest insects. An ical relationships with their hosts by Gordon exception to this generalization was the and Webster (23,24), Rutherford (49), and work of Glaser and his colleagues, of the Wtilker (59). However, only one species is New Jersey Department of Agriculture on the verge of commercial application, (United States),who steadily pursued a line namely Romanomermis culicivorax on mos- of research with rhabditid nematodes of the quitoes. Our knowledge of this nematode genus Neoaplectana. This was to provide a comes largely from 10 years of observations valuable base for subsequent applied stud- by Petersen (40-44) and colleagues at the ies. They spent several years examining the United States Department of Agriculture association of N. glaseri with the Japanese Laboratory at Lake Charles. Laird, of the beetle; subsequently they developed in vitro Research Unit on Vector Pathology in culture techniques for this nematode and Newfoundland, Canada has been a strong applied a similar species experimentally in advocate of the use of mermithids to control the field (21). In 1955 Dutky (17), at the biting flies in temperate and tropical cli- USDA Laboratory at Beltsville, pioneered mates (32). the use of the DD-136 strain of N. carpo- capsae for control of pest insects of orchards (17). This was followed in great anticipation INSECT PEST MANAGEMENT by applications of this species to pests of Despite tile long history of agriculture vegetable and field crops, forest crops, and and its success in progressively increasing to turf crops. crop productivity, the goal of optimum eco- During the same period Welch com- nomic production of a crop of high quality pleted his studies, at Rothamsted Experi- remains elusive. To achieve optimum qual- mental Station, England on entomophilic ity and economic production, the develop- nematodes of fruit flies and subsequently, ment of a sound pest management scheme at the Canada Department of Agriculture, is essential for each crop. To do this, a Belleville Laboratory, published a sequence systems approach constructed on a large of papers (eg. 54, 56) that demonstrated the data base should be used to enable simula- potential of nematodes for the control of tion and forecasting of the various biolog- pest insects. Into this gathering momentum ical, economic, and environmental events 272 Journal of Nematology, Volume 12, No. 4, October 1980 that provide information upon which the ogy, the fundamental obstacle to inte- pest manager can make his decision. grated control is epitomized in this Entomologists have been prolific in their conflict of short- and long-term goals. studies of pest biology, but there is a danger that research on modeling insect pest prob- We are now conscious of the energy lems might terminate in the publication of problem but insufficiently responsive to its a set of monographs rather than in the utili- solution. An energy shortage will hamper zation of the results in an interactive, ap- our ability to provide adequate nutrition plied programme. In nematology we have for the world's growing population. The just begun the modeling approach (30) on greater the energy shortage, the greater the plant-parasitic nematodes. Nothing has destruction of arable land and the higher been done using this technique with en- the costs of chemical pesticides. This pro- tomophilic nematodes to aid in an insect vides an additional stimulus to increase our pest management system. understanding of biological control and the Pest management is usually adopted use of pest management (51). Biological only when the traditional chemical control control agents may be added either by "in- methods have failed. Belated attempts in undation," whereby the introduced parasite difficult situations are not those likely to be is applied once in large numbers, or by "in- successful. The use of pest management oculation" (or augmentation), whereby the techniques, as distinct from those of pest parasite is added to the pest's environment control, is still not widespread, probably which is manipulated so as to enhance es- for the following reasons: tablishment of the parasite as a long-term factor influencing the insect population. 1) Growers have relied on the apparent Few cases of crop protection have occurred instant success from repeated use of as a result of inundative application. This relatively cheap, convenient chemical is probably because a successful parasite pesticides that have been marketed exhausts its supply of hosts, suffers high by companies willing to provide help mortality, and then is unable to suppress and advice on their application. the multivoltine pest individuals that were 2) Good growers have used sound cul- at the nonsusceptible stage at the time of tural practices that have helped to release. Using nematodes, the inundation minimize pest damage, but do not, on method may have an advantage where there their own, facilitate optimum crop is an inexpensive labour force to produce production. very large numbers of parasites at a rela- 3) Biological control methods which tively low cost. The inoculation method have been recommended have not al- using nematodes has been hampered by our ways been integrated with other con- inadequate knowledge of the enviromnental trol methods or with the interactive factors governing the establishment of such ecology of the crop and pest. Their a parasite population within the pest insect consequent failure extended the poor population. reputation of such techniques. For nematodes to be used successfully in 4) Our knowledge of the interaction of pest management schemes in either the in- insect pest populations and associated undative or inoculative fashion, adequate nematodes with their environment is understanding of a number of conditions insufficient to provide the data base are necessary (50): necessary for pest management de- cisions. I) Seasonal coincidence of the parasite 5) The goal of integrated control is to and host. obtain a high sustained yield with the 2) Ecological coincidence of the parasite least use of energy whereas, unfortu- and host. nately, most agricultural policies aim 3) Physiological acceptance by the host at maximizing short-term yields with of the parasite at the time of entry the associated great use of energy. As and during the parasite's endogenous Corbet (14) pointed out at the 1972 development. International Congress of Entomol- 4) Environmental tolerance by the para- Entomophilic Nematodes: Webster 273 site sufficiently long to locate and kill d) It maintains itself in the field for long its host (inundative application) or periods in the absence of the insect to establish itself as a parasite (in- host by feeding on its normal associ- oculative application). ate, the fungus. Hence, the problem 5) Biological competitiveness with other of synchrony of parasite and insect parasites and predators in the host's host life cycles at application is mini- ecosystem. mized. 6) Dispersal of the parasite in the inocu- e) The natural dispersal of Deladenus is lative application adequate to ensure readily achieved by the parasitized establishment. host. 7) Mass culture of the parasite inexpen- sively and rapidly, and the ability to A relatively minor unfavourable at- store these cultures. tribute of this nematode is that culture must be established in the field by the rather time- Four species of entomophilic nematode consuming inoculation of individual trees. came close to satisfying these conditions, and However, as a parasite introduced into a at present are being exploited on an experi- pest population by inoculation techniques, mental or commercial basis. it shows considerable promise, and evidence 1. Deladenus siricidicola is a parasite of to date suggests that DeIadenus is associated the woodwasp, Sirex noctilio, which is a with a decrease in Sirex-infested timber to pest of Pinus radiata. Since its introduction an acceptable level. into Australia from Europe, Sirex has be- 2. Neoaplectana carpocapsae has, through come a serious pest in the states of Tas- its strains and closely related species, a very mania and Victoria, where it has killed wide host range. Fourteen species of Neo- thousands of hectares of trees. After 10 years aplectana have been recorded from natural of laboratory and field research, first in infections in insects, and several of these Europe and later in Australia, Deladenus have been cultured on a large scale by a was released at a Sirex-infested location in variety of techniques (45). The ensheathed 1973 (2,4). The levels of parasitism of Sirex dauerlarvae of Neoaplectana species enter by this nematode increased rapidly, and this the insect's haemocoel and feed on the in- was followed by a decrease in the number troduced bacterium (Achromobacter nerna- of Sirex-killed trees. By 1977 no Sirex- tophilus) causing a lethal specticaemia in infested trees were located in the original the insect. 400 hectare site (5). In forests within 2-13 Favourable attributes of this group of kilometres of this site Sirex maintained its entomophilic nematodes are the following: level of attack, but recently Deladenus has started to spread naturally into these in- a) They can be cultured readily with fested areas. Bedding maintains (personal their associated bacterium, on agar communication) that wherever Deladenus slants, or mass produced in GaIleria parasitism has reached 70-95 % in the seeded rnellonella larvae (3,4,5,53). areas no serious outbreaks of Sirex remain. b) They may be readily stored for several Favourable attributes of this nematode months in an aerated, diluted forma- parasite are the following: lin solution at about 4°C. c) They can be conveniently applied as a) Large numbers are readily cultured in an "inundative" agent as either an the laboratory on the fungus (Amyl- aqueous spray (46,52,56) or by mixing ostereum chailletii) upon which it with a bait and placing on infested normally feeds during its alternate foliage. free-living cycle in the field. d) They are unharmed by many insecti- b) It is easily transported to seeding sites cides and in this respect are well either in Sirex-infested timber or as suited for integrated control meas- nematode cultures on fungal plates. ures. For instance, when the effective- c) It is not exposed to desiccation as the ness of N. carpocapsae was tested nematodes are inoculated into the against HyIernya on tobacco, it was timber. found to be as effective as diazinon 274 Journal of Nematology, Volume 12, No. 4, October 1980 but somewhat less convenient to ap- grams of infective R. culicivorax material ply (9). was required (44). Unfortunately, even this quantity did not kill all the mosquitoes in A major disadvantage of this group is the area. Although some people may be that if they do not penetrate their host im- satisfied with 60% control of some agricul- mediately, they are vulnerable to desicca- tural pests, medical entomologists require tion unless evaporation retardants are closer to 98% mortality of insect vectors of added to the aqueous suspension. A wide disease in order to obtain a period that is range of such retardants-fire retardants sufficient to break the transmission cycle. (52), glycerine (36), and oil/wax mixtures The ease with which mosquito larvae are (3)-have been tested to minimize nematode cultured is the basis for the success of mass desiccation. There are a large number of culture of R. culicivorax. However, in vitro records of field applications of Neoaplectana culture of mermithids would be preferable in a wide variety of habitats. Often this has because a nutrient balance at a level con- resulted in statistically significant decreases ducive to the optimum sex-ratio, rapid de- in the number of pests but economically in- velopment, and high nematode fecundity significant decreases in the pest population can be more easily maintained in culture and a failure to prevent crop depredation media. All these factors are likely influenced (25). Despite our incomplete knowledge of by the dynamic availability of nutrients. We the value of this genus in decreasing pest populations, N. carpocapsae is being pro- know, for instance, that female locust hosts duced commercially in France for applica- generally contain more nutrients than males tion against insect pests. and nymphs, and that developing Mermis 3. Romanomermis culicivorax, or Ree- nigrescens remain longer, grow larger, and simermis nielseni as it was formerly known, are more likely to become female in female is lethal to most species of mosquitoes which locusts. This implies that emergence from breed in permanent and semi-permanent the host may be influenced by the availabil- habitats. We now have a substantial pool of ity of a limiting nutrient or by the build-up knowledge on in vivo culture methods and of a toxic product in the haemocoel because on the environmental conditions necessary of the diminished ability of tile parasitized for survival of the pre- and post-parasites host to excrete (23). Our knowledge of the and for optimum infection of the host (2, nutrient requirements of mermithids (24) 41). Considerable progress has been made by and of their effect on the physiology and Nickle to satisfy government legislative biochemistry of the insect host (15,23,26,49) bodies in the United States so as to facilitate should ensure the successful culture of field application (38). mermithids on a synthetic medium. R. Favourable attributes of R. culicivorax culicivorax has been maintained in culture as a biological control agent are these: for several weeks on an in vitro medium (19), but growth and development was ab- a) It can be readily cultured on a mass normal. scale in mosquito larvae. Like other mermithids, R. cuIicivorax b) The gravid females and eggs are read- frequently has a patchy distribution and ily stored and transported to sites of greatly fluctuating population levels. Rub- field application. It is ideally used as stov (47) maintains that this is associated an "inoculative" agent but can be with an inability to reproduce and disperse effective as an "inundative" agent in rapidly. Poor dispersion results because the isolated habitats. mermithid usually kills its host before the c) It has a narrow host range, and its host matures. Mermithids ensure survival of lethal potential is restricted almost their species by balancing such factors as entirely to the culicids. However, poor dispersal against innate ability to in- there are records of laboratory infec- crease rapidly, and by responding to the tions of blackflies. influence of environmental factors, such as An example of the level of production inadequate food supply, with sex determina- necessary was a recent field trial against tion during ontogeny. Our understanding of anophelines in E1 Salvador where 700 kilo- the mechanisms of population density regu- Entomophilic Nematodes: Webster 275 lation in mermlthids remains incomplete. ical control agent to have cleared the whole Perutilimermis cuIicis was considered a pos- screening process (31). The United States sible alternative to R. culicivorax because it Environmental Protection Agency has al- is a parasite of adult mosquitoes which lowed commercialization of this mermithid would overcome the dispersal problem. on the basis that it is not a pesticide; rather However, its potential is limited because its it is a multicellular parasitic organism that host range is restricted to one mosquito does not vector bacteria or viruses but kills species. its host insects by making a hole in the There are many records of field applica- cuticle (during its own exit) resulting in tion of this nematode, but our knowledge of loss of haemocoelic fluid (38). its effect on the long-term decrease in mos- 4. Tetradonema plicans is a parasite of quito poptdations is limited because obser- sciarid fly pests of mushrooms. It possesses vations were terminated too soon. However, many attributes favourable for a biological Nickle (38) recently claimed that the R. control agent. It is a member of the culicivorax released in mosquito breeding Mermithoidea, and, like the mermithids areas in Maryland (United States) have themselves, one nematode sterilizes and kills perpetuated and caused 50-100% mortality the host (18). The female produces up to in the mosquito population after surviving 12,000 eggs; the life cycle is short; it can be two winters and minimum temperatures of readily cultured in vivo on sciarid flies --19 C. Petersen (personal communication) reared on horse dung (29); and the eggs can reports field infections persisting up to 6 be stored for several months at 10°C. Hence, years after application. it could be a useful agent against pests with R. culicivorax is unlikely to be an effec- short life cycles on rapidly growing crops, tive biological control agent in the vast especially in the humid and intensively mosquito-infested areas in the northern lati- managed environment of mushroom houses tudes, especially for spring Aedes species. (28). Despite the advantages of this nema- The temperatures in the snow-melt pools tode over many others as a biological con- are below the threshold for preparasite ac- trol agent, it has not been used extensively tivity. Hence, application rates of prepara- on a commercial basis. sites (50,000/m e) to achieve even a 30% infection under favourable conditions are THE FUTURE impractical with present mass culture tech- In the last 50 years we have moved from niques (20). species descriptions and biological record- Mermithids should be fully integrated ings of entomophilic nematodes to a fund into pest management programmes if their of knowledge on the taxonomy and biology full potential as biological control agents is of a wide range of species and the ability to to be realized. They are resistant to many culture and apply some of them in the lab- insecticides and are more host-specific than oratory and field to kill insects. chemical insecticides (33). We know that these nematodes cause There are now two reports that labora- insect mortality in field populations and tory-reared mosquitoes have developed re- exert some control over insect populations, sistance to a nematode biological control but it is difficult to determine accurately the agent. Anopheles quadrimaculatus larvae effect on an insect population. The estimate showed a twofold reduction in susceptibility o1 efficacy of the nematode as a biological to Diximermis peterseni after about 104 control agent depends on determining generations (58), and Culex pipiens quin- either the number of nematode-parasitized que[asciatus developed resistance to R. insects or the changes in the insect popula- culicivorax after 300 generations (42) but tion size over a given period. Neither of not after 100 (38). these methods is adequate to be of major The World Health Organization of the use in the large data base needed for insect United Nations has now developed a set of pest management. guidelines for screening the efficacy and Studying one factor at a time is the sci- safety of potential biological control agents. entist's usual approach to a complex prob- R. culicivorax is the only mosquito biolog- lem. In this way the contribution of each of 276 fournal of Nematology, Volume 12, No. 4, October 1980 the components of the complex can be eval- Proc. Int. Colloqium Invertebrate Pathology, King- uated and, hence, over time the whole prob- ston. 4. Bedding, R. A., and R. J. Akhurst. 1974. Use lem understood, i suggest that it is time to of the nematode Deladenus siricidicola in the bio- start putting the pieces together to see how logical control of Sirex noctilio in Australia. J. the parts interact. Future studies must be Aust. Ent. Soe. 13:129-135. on pest and parasite populations and on 5. Bedding, R. A., and R. J. Akhurst. 1977. Eval- uation of nematodes. In 1976-77 Annual Rept., pp. their interactions with one another and with 108-109. Division of Entomology, C.S.I.R.O. other factors in their ecosystem. Only then 6. Beirne, B. P. In press. Biological control-- shall we learn enough about the checks and benefits and opportunities. In: Perspectives in world balances affecting a particular host-parasite agriculture. Commonwealth Agricultural Bureaux, Slough, England. population to make informed decisions as 7. Brown, B. J., and E. G. Platzer. 1977. The to whether to inundate or inoculate the effects of temperature on infectivity of Roman- host's environment with a nematode para- omermis culicivorax. J. Nematol. 9:166-172. site, and when to do it. We are deficient in 8. Carson, R. 1962. Silent Spring. Houghton Mifflin, New York. our knowledge of the biological competitive- 9. Cheng, H. H., and G. E. Bucher. 1972. Field ness of nematodes when they are introduced comparison of the Neoaplectanid nematode DD-136 into a pest population. The commercial and with diazinon for control of Hylemya spp. on economic competitiveness between the pro- tobacco. J. Econ. Entomol. 65:1761-1763. duction of chemical pesticides and the mass 10. Cobb, N. A. 1920. One hundred new nemas. pp. 217-343. In Contributions to a science of nem- culturing of pathogenic nematodes is a sig- atology. Waverley Press, Baltimore. nificant obstacle. So also is the registration 11. Cobb, N. A. 1926. The species of Mermis. hurdle for all new insecticides, whether J. Parasit. 13:66-72. chemical or biological. Unfortunately, the 12. Cobb, N. A. 1927. Nemas sometimes aid man in his fight to control insect pests. USDA Yearbook great pressure on agricultural land and the of Agric.:479-480. need to rear disease-free plant and 13. Cobb, N. A., G. Steiner, and J. R. Christie. populations encourages an opportunistic 1923. Agamermis decaudata Cobb, Steiner and short-term pest control route which ignores Christie. A nema parasite of grasshoppers and other long-term implications. Such attitudes mili- insects. J. Agric. Res. 23:922-926. 14. Corbet, P. S. 1973. Application, feasibility tate against the use of pest management and and prospects of integrated control. In Insects, slow the introduction of nematode biolog- studies in population management, eds. P. W. Geier, ical control agents of insects. An organized C. R. Clark, D. J. Anderson, and H. A. Nix. pp. evolution fi'om nationally financed projects 185-195. Ecol. Soc. Aust. (memoirs 1), Canberra. 15. Craig, S. M., and J. M. Webster. 1974. In- to larger scale multinational ones may help hibition of molting of the desert locust, Schistocerea overcome some of the human as well as bio- gregaria, by the nematode parasite Mermis nigres- logical problems (6). cens. Can. J. Zool. 52:1535-1539. If we can alleviate these man-made pres- 16. Dujardin, F. 1842. Memoire sur la structure anatomique des Gordius et d'un autre helminthe, sures the potential for the successful use of le Mermis, qu'on on confondu avec eux. Ann. d. sc. entomophilic nematodes in pest manage- nat. 18:129-151. ment is high. We know several candidate 17. Dutky, S. R., and W. S. Hough. 1955. Note nematodes for insect management which we on a parasitic nematode from codling moth larvae, Carpocapsae pomonella (Lepidoptera, Olethreuti- can mass produce and apply. Let's take up dae). Proc. helminth. Soc. Wash. 57:244. Cobb's (10) enthusiasm and do itl 18. Ferris, J. M., and V. R. Ferris. 1966. Observa- tions on Tetradouema plicans on entomoparasitic nematode, with a key to the genera of the family LITERATURE CITED Tetradonematidae (Nematoda: Trichosyringida). Ann. Entomol. Soc. Amer. 59:964-971. 1. Bedding, R. A. 1968. Deladenus wilsoni n.sp. 19. Finney, J. R. 1976. The in vitro culture of and D. siricidicola n.sp. (Neotylenchidae), entomo- the mermithid parasites of mosquitoes and black- phagus-mycetophagous nematodes parasitic in siricid flies, pp. 225-226 In Proe. Int. Colloquium Inverte- woodwasps. Nematologica 14:515-525. brate Pathology, Kingston. 2. Bedding, R. A. 1972. Biology of Deladenus 20. Galloway, T. D., and R. A. Brust. 1976. Field siricidicola (Neotylenchidae) an entomophagous-- application of the mermithid nematode, Roman- mycetophagous nematode parasitic in siricid wood- t~mermis culicivorax Ross and Smith, for the control wasps. Nematologica 18:482-493. of mosquitoes, Aedes spp., in spring in Manitoba. 3. Bedding, R. A. 1976. New methods increase Manitoba Entomologist 10:18-25. the feasibility of using Neoaplectana spp. (Nem- 21. Glaser, R. W., E. E. McCoy, and H. B. Girth. atoda) for the control of insect pests, pp. 250-254. 1942. The biology and culture of Neoaplectana Entomophilic Nematodes: Webster 277 chresima, a new nematode parasite in insects. Proc. 40. Petersen, J. 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Effect of the Nemetode Contortylenchus brevicomi on Gellery Construction and Fecundity of the Southern Pine Beetle 1 A. E. MacGuidwin, G. C. Smart, Jr., R. C. Wilkinson, and G. E. Allen 2 Abstract: Field-collected Dendroctonus frontalis were reared in a controlled environment. Male-female beetle pairs retrieved from galleries 1, 2, or 5 wk after introduction into pine bolts were examined for nematode parasites. Data were obtained for each pair on gallery length, egg niche construction, egg viability, and progeny survival. In a separate study, beetle pairs were reared under laboratory conditions for 10 wk. The number of emerged adult progeny of each pair was recorded. Contortylenchus brevicomi, a nematode parasite, was found in 25% of all beetles that established galleries. After 2 and 3 wk, female beetles infected with the nematode had pro- duced fewer eggs and shorter galleries than did uninfected females. Uninfected females mated with nematode-infected males showed similar trends, although the differences in the 2- and 3-wk tests were not significant. Progeny survival or egg viability was not affected by nematode para- sitism of either parent beetle. Unikaryon minutum, a microsporidian parasite found in 65% of all colonizing beetles, had no effect on measured variables. The lower fecundity of beetles parasitized by C. brevicomi continued throughout the insect's reproductive cycle. After 10 wk, nematode-infected beetle pairs produced fewer emerged adult progeny than did uninfected pairs. Key Words: Dendroctonus frontalis, population dynamics, nematode-insect interaction.

The nematode Contortylenchus brevi- nematode progeny exit the host as fourth- comi (Massey) Rtihm parasitizes Dendroc- stage larvae. Adult males and preparasitic tonus lrontalis Zimmerman, the southern adult females are found within beetle gal- pine beetle, in 11 southern states (6,9, un- leries. Males are short-lived and die soon published data). Despite the widespread oc- after mating; impregnated females enter im- currence of the C. brevicomi-D. Irontalis mature stages of the beetle. interaction, the effect of nematode infection Nematode parasitism affects the flight on the distribution and abundance of south- ability (1,3), gallery construction (12), ern pine beetle populations is not known. emergence (1,11), and longevity (1,12) of C. brevicomi females parasitize all stages some bark beetles. Reduced fecundity as a of the southern pine beetle but do not com- result of nematode parasitism has been ob- mence oviposition until the beetle host served also in several species of bark beetles reaches maturity. C. brevicomi resembles (1,11,12,14). Contortylenchus elongatus (Massey) Nickle The purpose of this study was to deter- in life cycle (7). According to Nickle (10), mine the effect of C. brevicomi infection of many adult female nematodes and several D. [rontalis on the gallery construction, egg thousand eggs and larvae may be present production, egg viability, and progeny sur- in the hemocoel of an infected host. The vival of beetles reared for l, 2, or 3 wk under laboratory conditions. Also investigated was Received for publication 2 November 1979. the effect of nematode parasitism on the 1Based in part on an M.S. thesis submitted to the Uni- versity of Florida by the senior author. Supported in part number of progeny produced in one genera- by SEA CSRS Grant No. 580-15-3. tion by the southern pine beetle. 2Graduate Research Assistant and Professors, respectively, Department of Entomology and Nematology, University of Florida, Gainesville, FL 32611. We gratefully acknowledge the assistance of Dr. John MATERIALS AND METHODS Cornell, LF.A.S. Statistician, University of Florida, Gaines- ville, FL 32611. Beetles used in these tests emerged from Florida Agricultural Experiment Stations Journal Series No. 2022. one loblolly pine (Pinus taecla) tree brought