View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Érudit Article "Entomopathogenic Nematodes – Save Biocontrol Agents for Sustainable Systems" Ralf-Udo Elhers Phytoprotection, vol. 79, n° 4, 1998, p. 94-102. Pour citer cet article, utiliser l'information suivante : URI: http://id.erudit.org/iderudit/706164ar DOI: 10.7202/706164ar Note : les règles d'écriture des références bibliographiques peuvent varier selon les différents domaines du savoir. Ce document est protégé par la loi sur le droit d'auteur. L'utilisation des services d'Érudit (y compris la reproduction) est assujettie à sa politique d'utilisation que vous pouvez consulter à l'URI https://apropos.erudit.org/fr/usagers/politique-dutilisation/ Érudit est un consortium interuniversitaire sans but lucratif composé de l'Université de Montréal, l'Université Laval et l'Université du Québec à Montréal. Il a pour mission la promotion et la valorisation de la recherche. Érudit offre des services d'édition numérique de documents scientifiques depuis 1998. Pour communiquer avec les responsables d'Érudit : [email protected] 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 bacteria. They totally dépend on trans­ mission by the DJ into a stérile environ­ ment like the insect's haemocoel, as Steinernema and Heterorhabditis (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 nematode 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