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"Entomopathogenic – Save Biocontrol Agents for Sustainable Systems"

Ralf-Udo Elhers Phytoprotection, vol. 79, n° 4, 1998, p. 94-102.

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Document téléchargé le 13 février 2017 04:56 Research Challenges and Needs for Safe Use of Arthropods

Entomopathogenic Nematodes - Save Biocontrol Agents for Sustainable Systems

Dr. Ralf-Udo Ehlers

Institute for Phytopathology, Christian-Albrechts-University Kiel, Dept. Biotechnology & Biol. Control, Klausdorfer Str. 28-36, 24223 Raisdorf, Germany

BIOLOGY . They totally dépend on trans­ mission by the DJ into a stérile environ­ ment like the insect's haemocoel, as and (Rhab- they lack any means for survival in the ditida) are symbiotically associated with soil environment (Morgan et al., 1997) bacteria of the gênera Xenorhabdus and or invasion of insect's haemocoel with- Photorhabdus within the Enterobacteri- out the help of the DJ. Whereas Stein­ aceae in the gamma subdivision of ernema spp. can kill insects even with- purple bacteria (Ehlers et ai, 1988), out their symbiotic bacteria (Ehlers et respectively. Each species al., 1997), Heterorhabditis spp. lack in­ has a spécifie association with one sect pathogenicity in the absence of P. bacterium species (Akhurst & Boemare, luminescens. Bowen & Ensign (1998) 1990; Ehlers & Niemann, in press). Like identified insecticidal proteins produced other nematodes of the order Rhabditi- by P. luminescens with potential to da, Steinernema and Heterorhabditis substitute Bt toxins in transgenic plants. spp. form dauer (enduring) juvéniles (DJs), which are morphologically and Host-finding behaviour of DJs can physiologically adapted for long term differ within a population and can also survival in the soil environment (Wom- be species spécifie. "Hunters" are high- ersley, 1993; Glazer, 1996). DJs can be ly mobile and a large proportion of their isolated from almost ail habitats where population tends to actively seek for soil insects occur. Whereas the few Het­ suitable hosts. In populations of S. gla- erorhabditis species are distributed ail seri and Heterorhabditis spp. the ma­ around the world, the majority of the jority of the individuals show this char- Steinernema species seem to be restrict- acter. The sit-and wait "ambushers" ed to certain geografical régions and often attach to soil particles and nictate, other species, e.g. S. feltiae, are widly waiting for an insect to pass by and distributed (Hominick et al., 1996). The then attack. S. carpocapsae is a species nematode dauer juvéniles (DJ) carry with this behaviour (Gaugler, 1993). Q. Q. between 0to250cellsof theirsymbiont Pénétration of the host insect occurs 3 w in the anterior part of the intestine. The via naturalopeningsordirectlythrough symbiotic bacteria are released into the the insect cuticle (Bedding & Molyneux, r» haemolymph after pénétration of the 1982; Peters & Ehlers, 1994). There are DJ into a suitable host insect. Inside the indications that the pénétration process DJ the bacteria are well protected is supported by proteolytic factors pro­ against detrimental conditions in the duced by the exsheathed dauer juvé­ soil. Neither Xenorhabdus nor Photo­ nile (Roque et al., 1994). Upon reaching rhabdus spp. hâve ever been isolated the haemocoel the DJ is recognized as from soil environments (Akhurst & non-self and insect défense mechanisms Boemare, 1990; Poinar, 1990). Accord- can eliminatethe DJsthrough encapsu- ingly, this phoretic relation seems to be lation (Peters & Ehlers, 1997). Defence of vital necessity for the associated mechanisms against the bacteria also

94 hâve been described (Gôtz et al., 1981). genicity (Boemare et al., 1996, Ehlers & Providing the insect's défense mecha- Hokkanen, 1996). Besides what has been nisms fail to eliminate the nematode- published in the scientifc literature, bacterium complex, the insect dies 2-4 safety tests hâve been conducted by days after infection. Akhurst & Dunphy the Pasteur Institute (Boemare et al., (1993) and Simoes & Rosa (1996) hâve 1996) and by commercial companies. summarized the current knowledge on Although thèse results hâve not been the pathogenicity mechanisms of the made public, the documentation was nematode-bacterium complex and the provided to the US agency APHIS. No interactions with the défense System of attributes of the nematodes could be host insects. Once established inside identified which would prohibit their use the cadaver, the bacteria proliferate and in biocontrol (R. Georgis, personal com­ produce suitable conditions for the munication; Parkman et al., 1992). nematode to grow and reproduce. The The consensus view of the partici­ nematodes feed on cells of their sym- pants of a combined OECD and COST biont and host tissue. Without the prés­ 819workshopon introduction and com­ ence of the symbiotic bacteria in the mercial use of non-endemic nematodes insect cadaver the nematodes are un- for insect biological control (Ehlers & able to reproduce (Poinar & Thomas, Hokkanen, 1996) was that entomopatho­ 1966). Infective DJs of Stelnernema genic nematodes (EPNs) possess spé­ develop to amphimictic adults and cifie biological and ecological features, Heterorhabditis spp. to self-fertilizing which make their use in biological con­ hermaphrodites. Their offspring either trol exceptionally safe. Ail of the scien- develop to DJs or to a F1 adult génér­ tific évidence available supports the ation. Another adult génération (F2) is conclusion that EPNs are safe to the usually not developed. Instead, in re- environment, as well as to the produc­ sponse to depleting food resources, DJs tion and application personnel, to the are formed. Two to three weeks after gênerai public, and to the consumers of colonisation of the host insect, the DJs agricultural productstreated with EPNs. leave the cadaver searching for new Only a few potential, but very remote target insects in the soil. risks could be identified (Tab. 1 & 2). Therefore it was recommended that EPNs should not be subject to any kind SAFETY AND of registration. REGISTRATION The introduction of non-endemic nematode species, however, should be Entomopathogenic nematodes and their regulated. Species should be accurate- symbionts are environmentally safe and ly identified, détails of the origin, known show no évidence of mammalian patho­ distribution, probable host range and

Table 1. Possible risks to human heaith as identified by the expert group. Scale: 0 = no risk at ail, 1 = remote, 2 = slight, 3 = moderate, 4 = high, 5 = very high risk.

Production & Application Personnel General Public Toxicity Allergenicity Infectivity nematodes bacteria Carcinogenicity Teratogenicity Food and Feed Pathogenicity of hot-adapted strains

95 Table 2: Possible environmental risks of using EPNs, as identif ied by the experts. Risk rating as in Table 1. NTO = Non-Target Organsims

Possible environmental risks Rating

1. Non-target organisms (NTOs) In untreated fields In treated fields - in the soil - in other cryptic environments - on foliage Vertebrates - warm blodded - cold blooded Invertebrates Arthropods - Predators - Parasitoids - Pollinators - Rare or endangered species - Others Non Arthropods - Earthworms - Others Plants

2. Compétitive displacement of native EPN in treated fields - Temporary - Permanent

3. Changes in ecosystem balance - Local temporary suppression of NTOs - Permanent suppression of NTOs

4. Contamination of ground water

5. Gène transfer from exotic symbiotic bacteria to other soil bacteria

6. Biological "pollution" with new EPN species

7. General biodiversity

its safety to the user must be provided COMMERCIAL USE OF EPNs together with an expert opinion based on available information of the possi­ Nematodes can be mass produced in in a a ble impact on non-target organisms. vitro culture. Their symbiotic bacteria 3 Nematodes are bénéficiai animais and can convert protein-rich média into c/> although symbiotically associated with suitable resources for the nematodes. bacteria, in most countries they are not A significant breakthrough in nematode placed in the category of microorgan- biotechnology was the discovery of the isms for pest control. As such they are symbiotic bacterium by Poinar & Tho­ usually exempted from registration re- mas (1965) and the development of in quirements, as documented for the vitro production techniques on solid United States by Gorsuch (1982). This substrates applicable for nematodes of makes the commercial development of both gênera (Bedding, 1981, 1984). nematode products even more attrac­ Since then the commercial use of nem­ tive for industry as large costs related atodes in high value crops in horticul­ with registration can be avoided. ture started. In industrilized countries

96 the labour-intensive solid state produc­ be successfully controlled. The mole tion is often substituted by liquid cul­ cricket Scapteriscus vicinus is controlled ture in bioreactors. Liquid mass pro­ with S. scapterisci in Florida and Geor- duction started with S. carpocapsae, gia (Redmond & Georgis, 1993). White which was scaled up to 80.000 Itr. (Fried- grubs (Scarabaeidae) in turf can be man, 1990). Yields of Heterorhabditis managed by application of Heterorhab- spp. liquid cultures are still highly vari­ ditisspp. (e.g., Georgis &Gaugler, 1991; able (Ehlers et al., 1998). In the future, Klein & Georgis, 1992, Downing, 1994, commercial development will rely sole- Sulistyanto & Ehlers, 1996). In China ly on liquid culture technology as this the peach borer {Carposina nipponen- is the only means for a development of sus) is an important pest of apples and nematode-based products for agricul- pears (Jinxian, 1993), and several hun- tural markets at economically reason- dred hectares are already treated with able priées. S. carpocapsae (Doeleman, 1990). Also in China, this nematode is successfully The art of nematode formulation tech­ introduced to control the cossid car- nology is to define and maintain envi- penterworm Holocerus insularis in ronmental conditions which transfer the shade trees (Huaiwen et al., 1993; Jinx­ DJ into a quiescent state from which it ian, 1993). S. carpocapsae is also used can immediately recover when placed against flea larvae and pupae in soil in into the spraying tank. Formulation the USA. compounds, like clays or biopolymers, hâve the function to immobilize the nematodes, and ail kinds of adjuvants EPNs IN SUSTAINABLE and additives préserve favourable con­ ditions for the nematode. Sufficient gas SYSTEMS exchange and a stable moisture con­ tent hâve to be preserved. Shelf life of Little is known about the impact of nematode based products of a few naturally occuring EPN populations. The months is nowadays achieved at ambi- observations reported so far can be ent températures not exceeding 30°C. divided into relatively balanced host- The DJ is résistant to shear forces and nematode associations and epizootics. can bear pressure of 2,000 kPa (Geor- The association of S. krausseiwWh the gis, 1990), which is why DJs can be false spruce webworm, Cephalcia abi- sprayed with conventional spraying etis, in Central Europe is an example for equipment. a balanced System with a cumulative annual control of approximately 25% In the overall turnover in the biocon- (Mracek, 1986; Eichhorn, 1988). In Aus- trol market, EPNs hâve reached the tria Fùhrer & Fischer (1991) used lime second position after Bacillus thuring- to increase the soil pH in forest Systems iensis based products. Currently seven in order to enhance the host finding of companies in Europe produce EPNs the natural nematode popuation and for commercial application. In 1994 they could increase the nematode in­ world-wide nematode sales surpassed festation of C. abietis. Another example $US 10 million. In Europe and the USA, for an attempt to increase the naturally larvae of the black vine weevil Otio- occurring EPN population by cultural rhynchus sulcatus are controlled in methods is reported by Brust (1991). strawberries, craneberries, ornamentals No-tillage and less intense weed con­ and tree nurseries with Heterorhabditis trol resulted in higher levels of nema­ spp., S. feltiae or S. carpocapsae (Geor- tode infestation, significantly higher gis, 1992). Treatments in citrus planta­ corn yields and less root damage by the tions reduce root weevils (Curculion- corn rootworm Diabrotica undecim- idae) by 50-65% (Downing et al., 1991; punctata howardi. Schroeder, 1990, 1992). Sciarid flies (Sciaridae) in mushroom cultures are Epizootics hâve been observed in reduced by S. feltiae strains by 51- grub populations infested with Heter­ 94% (Grewal & Richardson, 1993; Gre- orhabditis sp. reaching 71% control in wal et al., 1993). Turf insect pests can a sugarcane field (Akhurst et al., 1992)

97 and 80% in the population of the gar- agriculture markets,the production also den chafer Phyllopertha horticola (Pe- becomes a logistic problem. The capac­ ters, 1996). In New Zealand an increas- ity and timing of mass production needs ing infestation reaching 56% after a to be adapted to the market's seasonal one-time release of H. bacteriophora demand (von Reibnitz & Backhaus, was reported in the second year (Jack­ 1994). To make available such quanti­ son & Wouts, 1987). Since four years H. tés of entomopathogenic nematodes, bacteriophora is used inundatively in the technology needs to be reproduc- Germany to control grubs (P. horticola) ible, liquid culture yields need to be in turf. On many plots treated with nem- further increased and DJ quality must atodes the grub population was below be stabilized. the damage threshold in following years (Ehlers & Peters, 1998). Thèse observa­ Significant progress also is needed tion encourage further research to in- in the improvement of the post harvest vestigate the conditions necessary to and application technology. Large nem- obtain long-term effects through nem- atode quantaties can only be handled atode inoculation. when storage technology can guaran- tee a survival of the DJs at high quality. The distribution of EPNs in the field The objective of formulation improve­ seems to be related to the distribution ment is to guarantee a shelf life of of potential host insects. As the distri­ approximately 6 months at ambient bution of soil insect populations are température. This is already achieved usually patchy, the same is recorded with some, but not ail nematode spe­ for nematodes. Those species with a cies. For field use, low volume applica­ wide host range, e.g. S. feltiae, are found tion technology and the lack of irriga­ in almost every second soil sample, tion facilities must also be considered. whereas Heterorhabditis spp. are sel- Currently, nematodes are applied with domly encounted. The latter seem to high volumes of water. Future efforts hâve the potential to cause epizootics will hâve to consider adjuvants and and thus hâve a potential for inocula- additives in order to decrease the tive release. Their potential for long term amount of water necessary for nema­ survival seems to be poor. In contrast, tode application in the field. Research S. feltiae is able to survive for long and development in application tech­ périodes without hosts available and nology will also focus on an overall thus is more abundant, but has not been réduction of the nematode application observed to control more than 20% of density. Many of the nematodes applied a potential host population. never reach a target host (Curran, 1993). Nowadays, EPNs are used inunda­ The improvement of the application tively, however, the reports of natural technology and of the nematode's con­ occurance, their potential for long-term trol potential by genetic means (Burnell control and possible cultaral means of & Dowds, 1996) are possible measures stabilizing their population should en­ to reduce the application density in the courage research to investigate their field. Together with progress in the liq­ potential as antagonists in sustainable uid culture technology this will signifi- Systems. cantly contribute to lower application costs. In conventional agriculture Systems FUTURE PERSPECTIVES biocontrol products can not compete with chemical control measures. There- Currently, the market size in the différ­ fore biologicals are only used in situa­ ent countries seldomly surpasses treat- tion were chemicals fail, either due to ments of 500 hectares. The use in out- résistance of the insect population orto door crops would involve much larger survival in cryptic environments, or areas and consequently a an increase when the chemical control is restricted in liquid culture capacity. Considering by législation. Chemical compounds are the short shelf life of nematodes and to be degraded in the environment the seasonal variation in the demand of within two weeks after application,

98 persistent pesticides hâve been banned. - Another question is whether societ- In contrast, the impact of biologicals ies are willing to support the devel­ can be long lasting. Sustainable agri­ opment of biocontrol agents and will culture and ecological farming practice subsidies costs related tosafety tests? will rely on the potential of biologicals. - Biocontrol in sustainable Systems will They can either develop cultural meth- rely on a spectrum of possible agents. ods to increase and maintain the poten­ Are our politicians prepared to re­ tial of antagonistic populations or, in the case where the antagonist is ab­ duce the costly hurdles which are sent, they will rely on inundative re- currently related with registration of lease. Sustainability will largely dépend microbial agents? on biological régulation of pest popula­ tions and EPNs contribute to the overall antagonistic potential in soil environ- REFERENCES ments. AKHURST, R. J., BEDDING, R. A., BULL, R. EPNs hâve many advantages over M., & SMITH, R. J. (1992) An epizootic of Heterorhabditis spp. (Heterorhabditidae: other control agents. They can be ap- Nematoda) in sugar cane scarabaeida plied with conventional spraying equip- (Coleoptera). Fundamental & applied ment, chemical compounds cannot in­ Nematology, 15, 71-73. terfère with their control potential and AKHURST, R. J. & BOEMARE, N. E. (1990) they are usually exempted from regis- Biology and of Xenorhabdus, tration (Ehlers & Peters, 1995). Like in Entomopathogenic Nematodes in microbial agents nematodes can easily Biological Control (GAUGLER, R. &. be mass produced in liquid culture and KAYA, H. K., Eds) CRC Press, Boca Raton, stored maintaining their control poten­ pp. 75-90. AKHURST, R. J. & DUNPHY, G. B. (1993) tial for considérable time (Ehlers, 1996). Tripartite interactions between symbiot- They hâve a potential in inundative and ically associated entomopathogenic inoculative release and hâve insignifi- bacteria, nematodes, and their insect cant effects on non-target organisms hosts, in Parasites and Pathogens of In- (Bathon, 1996). They are mobile in the sects - Volume 2: Pathogens (BECKAGE, soil environment and can persist for N. E., THOMPSON, S. N. & FEDERICI, years. B. A., Eds). Académie Press, San Diego, pp. 1-23. Other microbiais need registration BEDDING, R. A. (1981) Lowcost in-vitro mass and the costs related with the registra­ production of Neoaplectana and Heter­ tion cannot be justified taking into con­ orhabditis species (Nematoda) for field sidération the size of the potential control of insect pests. Nematologica21, markets. Transgenic plants met the 109-114. same conditions as their development BEDDING, R. A. (1984) Large scale produc­ tion, storage and transport of the insect- is equally expensive and they will be parasitic nematodes Neoaplectana spp. available only in the large scale mar­ and Heterorhabditis spp. Annals of Ap­ kets. As long as registration policy is plied Biology 104, 117-120. not changed, marketing of microbial BATHON, H. (1996) Impact of entomopatho­ control agents is prevented and nema­ genic nematodes on non-target hosts. todes will probably be the number one Biocontrol Science and Technology 6, agents for insect control in soil environ- 421-434. ments. BEDDING, R. A. & MOLYNEUX, A. S. (1982) Pénétration of insect cuticle by infective - The question is whether long-term juvéniles of Heterorhabditis spp. (Heter­ sustainable effects can be measured? orhabditidae: Nematoda). Nematologica Quantification of nematode popula­ 28, 354-359. tions is almost impossible and usual­ BOEMARE, N. E., LAUMOND, C. & MAULE- ly we cannot distinguish between ON, H. (1996) Biology of nematode-bac- terium complex. Biocontrol Science and released and endémie populations. Technology 6, 333-345. Increases in yields of 5% or more are within the confidentiality range of our data.

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100 GEORGIS, R. & GAUGLER, R. (1991) Predict- MORGAN, J. A. W., KUNTZELMAN, V., TAVE- ability in biological control using ento- NOR, S., OUSLEY, M. A. & WINSTAN- mopathogenic nematodes. Journal of LEY, C. (1997) Survival of Xenorhabdus Economie Entomology 84, 713-720. nematophilusand Photorhabdus lumine- GLAZER, I. (1996) Survival mechanisms of scens in water and soil Journal of Ap­ entomopathogenic nematodes. Biocon- plied Microbiology 83, 665-670. trol Science and Technology 6, 373-378. MRACEK, Z. (1986) Nematodes and other GORSUCH, A. M. (1982) Régulations for the factors controlling the sawfly Cephalcia enforcement of the FIFRA exemption from abietes (Pamphilidae: Hymenoptera), in régulation of certain biocontrol agents. Czechoslovakia. Forest Ecology & Man­ US Fédéral Register 47-23928-23930. agement, 15, 75-79. GÔTZ, P., BOMAN, A. & BOMAN, H. G. (1981) PARKMAN, J. P., THURSTON, G. S. & Interaction between insect immunity and GAUGLER, R. (1992) Proceedings of the an insect-pathogenic nematode with sym- bénéficiai nematode panel, in Proceed­ biotic bacteria. Proceedings ofthe Royal ings ofa USDA/CSRS National Workshop: Society London B212, 333-350. Régulations and Guidelines: Critical Is­ GREWAL, P. S., GAUGLER, R. & SELVAN, S. sues in Biological Control (CHARUDAT- (1993) Host récognition by entomopatho­ TAN, R. & BROWNING, H. W., Eds) Insti- genic nematodes: behavioral responseto tute of Food and Agricultural Sciences, contact with host fèces. Journal of Chem­ Universityof Florida, Gainesville, pp. 173- ical Ecology 19, 1219-1231. 176. GREWAL, P. S. & RICHARDSON, P. N. (1993) PETERS, A. (1996) The natural host range of Effects of application rates of Steinerne- Steinernema and Heterorhabditis spp. ma feltiae (Nematoda: Steinernematidae) and their impact on insect populations. on biological control of the mushroom Biocontrol Science & Technology 6, 389- fly Lycoriella auripila (Diptera: Sciaridae). 402. Biocontrol Science and Technology 3, PETERS, A. & EHLERS, R.-U. (1994) Suscep- 29-40. tibility of leatherjackets {Tipula paludosa HOMINICK, W. M., REID, A. P., BOHAN, D. A. and T. oleracea; Tipulidae: Nematocera) & BRISCOE, B. R. (1996) Entomopatho­ to the entomopathogenic nematode genic nematodes: biodiversity, geograph- Steinernema feltiae. Journal of Inverte- ical distribution and the Convention on brate Pathology 63, 163-171. Biological Diversity. Biocontrol Science PETERS, A. & EHLERS, R.-U. (1997) Encap- and Technology 6, 317-331. sulation of the entomopathogenic nem­ HUAIWEN, Y., GANGYING, Z., SHANAGO, atodes Steinernema feltiae in Tipula ol­ Z. & HENG, J. (1993) Biological control of eracea. Journal of Inverte b rate Pathology tree borers (Lepidoptera: Cossidae) in 69, 218-222. China with the nematode Steinernema POINAR, G. 0., JR. (1990) Biology and tax- carpocapsae, in Nematodes and the Bio­ onomy of Steinernematidae and Heter- logical Control of Insect Pests (BEDDING, orhabditidae in Entomopathogenic Nem­ R., AKHURST, R. J. & KAYA, H. K., Eds) atodes in Biological Control (GAUGLER, CSIRO, East Melbourne, pp. 33-40. R. & KAYA, H. K., Eds) CRC Press, Boca JACKSON, T. A. & WOUTS, W. M. (1987) Raton, pp. 23-61. Delayed action of an entomophagous POINAR, G. 0., JR., &THOMAS, G. M. (1965) nematode Heterorhabditis sp. (V16) for A new bacterium, Achromobacter nem­ grass grub control. Proceeding ofthe 40th atophilus sp. nov. (Achromobacteriace- New Zealand Weed and Pest Control ae: Eubacteriales), associated with a Conférence, 33-35. nematode. International Bulletin of Bac- JINXIAN,W. (1993) Control ofthe fruit moth, teriological Nomenclature and Taxono- Carposina niponensis, using ento­ my, 15, 249-252. mopathogenic nematodes, in Nematodes POINAR, G. O., JR. &THOMAS, G. M. (1966) and the Biological Control of Insect Pests Significance of Achromobacter nemato­ (BEDDING, R., AKHURST, R. J. & KAYA, philus Poinar and Thomas (Achromobac- H. K., Eds) CSIRO, East Melbourne, pp. teriaceae: Eubacteriales) in the develop- 59-65. ment of the nematode, DD-136 KLEIN, M. G. & GEORGIS, R. (1992) Persis- (Neoaplectana sp., Steinernematidae). tence of control of Parasitology 56, 385-390. (Coleoptera: Scarabaeidae) larvae with REDMOND, C. T. & GEORGIS, R. (1993) steinernematid and heterorhabditid nem­ Entomopathogenic nematodes as bio­ atodes. Journal of Economie Entomolo­ pesticides for control of turfgrass insects, gy 85, 727-730. in International Turfgrass Society Re­ search Journal 7, 398-404.

101 ROQUE, P., RIBEIRO, C, CRUZ, N. & SIMO- SULISTYANTO, D. & EHLERS, R.-U. (1996) ES, N. (1994) Chemical factors released Efficacy ofthe entomopathogenic nema­ by correlated todes Heterorhabditis megidis and Het- with the pénétration in the insect host, in erorhabditis bacteriophora to control Sixth International Colloquium on Inver- grubs (Phyllopertha horticola and Aph- tebrate Pathology and Microbial Con- odius contaminatus) in golf course turf. trol - Second International Conférence on Biocontrol Science and Technology 6, Bacillus thuringiensis Society for Inverte- 247-250. brate Pathology, Montpellier, p. 277. VON REIBNITZ, C. & BACKHAUS, G. F. (1994) SCHROEDER, W. J. (1990). Entomopatho­ Untersuchungen zum Bedarf biologischer genic nematodes for root weevil control Pflanzenschutzverfahren gegen Otiorhyn- in citrus, in Proceedings ofthe Fifth Inter­ chussjpp. im Gartenbau und zur Kosten- national Colloquium of Invertebrate Pa­ struktur der Produktionsverfahren fur thology and Microbial Control, Society entomopathogen Nematoden (Heter­ for Invertebrate Pathology, Adélaïde, orhabditis). Gartenbauwissenschaft 59, p. 267. 199-206. SCHROEDER, W. J. (1992) Entomopathogenic WOMERSLEY, C. Z. (1990) Dehydration sur- nematodes for control of root weevils of vival and anhydrobiotic potential, in En­ citrus. Florida EntomologistlS, 563-567. tomopathogenic Nematodes in Biologi- SIMOES, N. & ROSAS, J. S. (1996) Pathoge- cal Control (GAUGLER, R. & KAYA, H. K., nicity and host specificity of ento­ Eds) CRC Press, Boca Raton, pp. 117-138. mopathogenic nematodes. Biocontrol Science & Technology 6, 403-411.

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