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Christine T. Griffin - One of the best experts on this subject based on the ideXlab platform.

  • Conditioning the entomopathogenic nematodes Steinernema carpocapsae and Heterorhabditis Megidis by pre-application storage improves efficacy against black vine weevil, Otiorhynchus sulcatus (Coleoptera: Curculionidae) at low and moderate temperatures
    Biological Control, 2017
    Co-Authors: Adam Guy, Michael Gaffney, Apostolos Kapranas, Christine T. Griffin
    Abstract:

    Abstract Entomopathogenic nematodes (Heterorhabditis spp. and Steinernema spp.) are effective biocontrol agents for several insect pests, but their use is restricted by environmental constraints such as temperature and by their high cost. Use of nematodes against vine weevil (Otiorhynchus sulcatus) is restricted by low temperatures prevailing at the time when control is required. Here we investigate the potential for “conditioning” – storing nematode infective juveniles at 9 °C for at least three weeks prior to application – to improve efficacy, both at low and moderate temperatures. Conditioned Heterorhabditis Megidis were previously shown to give improved control of vine weevil when applied to potted plants at constant 9 °C. Here we show similar results for Steinernema carpocapsae conditioned for 3–6 weeks at 9 °C. We also show that conditioning (3 weeks pre-application storage at 9 °C) improved efficacy of both species against vine weevil in strawberries grown in bags in an unheated glasshouse at 0–12 °C. In a final experiment, we also test whether improved performance of 9 °C-stored H. Megidis compensates for a reduced application rate at a more permissive temperature, 15 °C. Conditioned H. Megidis gave control equal to that of unstored H. Megidis applied at double the rate. Commercial product based on the cold-active species Steinernema kraussei was used as a reference treatment in all experiments. At constant 9 °C, S. kraussei gave control superior to that of both unstored and conditioned H. Megidis and S. carpocapsae, while at constant 15 °C, both conditioned and unstored H. Megidis applied at half the recommended rate gave superior control to S. kraussei applied at full rate. Repetition of experiments with vine weevil larvae of increasing age indicated that success of S. kraussei is more influenced by larval age than that of the other two species, and that this species is more effective against younger (2nd–3rd) than older (4th–7th) instars.

  • Survival, starvation, and activity in Heterorhabditis Megidis (Nematoda: Heterorhabditidae)
    Biological Control, 2006
    Co-Authors: Paul F.l. Fitters, Christine T. Griffin
    Abstract:

    Infective juveniles (IJs) of entomopathogenic nematodes do not feed but have ample stored energy reserves and can survive for several months in soil or in water. Intraspecific variation in survival of Heterorhabditis Megidis has been observed for eight isolates of H. Megidis stored in water at 20 °C for up to 14 weeks with the 50% survival time (ST50) ranging from 5.6 to 12.5 weeks. How important physical and behavioral attributes were in explaining this variation in survival was explored using stepwise regression. Included in the analysis were: initial energy reserves (measured by image analysis densitometry), size (area and length) the time at which 50% of energy reserves were depleted (ET50), and motility (head movements/min in week 0). Energy depletion rate, ET50, is an important predictor of survival, explaining 93.8% of the variation in ST50 among isolates. Energy depletion rate was highest in the first week, a time at which H. Megidis IJs were spontaneously active during storage. By week 5, when IJs had begun to die, some individuals had completely depleted their energy reserves, supporting the hypothesis that death was a result of starvation. In a second stepwise regression, performed to explore what factors contribute to variation in rate of energy depletion, motility accounted for 60.1% of the variation in ET50. With the inclusion of initial energy reserves, length, and area, 88.5% of the variation was accounted for. We conclude that intraspecific variation in survival of H. Megidis in water is due largely to variation in rates of depletion of energy reserves, which in turn is strongly associated with levels of locomotory activity.

  • Effects of Paenibacillus nematophilus on the entomopathogenic nematode Heterorhabditis Megidis.
    Journal of invertebrate pathology, 2004
    Co-Authors: Michael R. Enright, Christine T. Griffin
    Abstract:

    The insect parasitic nematodes Heterorhabditis spp. are mutualistically associated with entomopathogenic bacteria, Photorhabdus spp. A novel association has been detected between H. Megidis isolate EU17 and the endospore-forming bacterium Paenibacillus nematophilus. P. nematophilus sporangia adhere to infective juveniles (IJs) of H. Megidis and develop in insect hosts along with the nematodes and their symbiont. We tested the effects of P. nematophilus on H. Megidis. The yield and quality (size, energy reserves, and storage survival) of IJs were not affected by co-culture in insects with P. nematophilus. Dispersal of IJs in sand and on agar was inhibited by adhering P. nematophilus sporangia: fewer than 2% of IJs with P. nematophilus sporangia reached the bottom of a sand column, compared to 30% of the control treatment. Sporangia significantly reduced infectivity of H. Megidis for wax moth larvae in sand, but not in a close contact (filter paper) assay. The results suggest that P. nematophilus may reduce the transmission potential of H. Megidis through impeding the motility of IJs.

  • Spontaneous and induced activity of Heterorhabditis Megidis infective juveniles during storage
    Nematology, 2004
    Co-Authors: Paul F.l. Fitters, Christine T. Griffin
    Abstract:

    Infective juveniles (IJ) of three Heterorhabditis Megidis isolates, HF85, EU17 and UK211, were stored in water at 20°C for up to 10 weeks. At 2-week intervals, activity, infectivity, energy reserves and survival were measured. There was no difference between the three isolates in infectivity, which increased significantly over the first 2 weeks and declined gradually thereafter. IJ became inactive during storage. Out of storage, the highest activity was recorded in week 0: nearly all IJ were active within the first minute of observation and remained active for the 20-min observation period. With increasing storage time, an increasing proportion of IJ were inactive in the first minute, reaching 83–96% by week 6. The time taken by 50% of the IJ to become active (AT50) initially increased with nematode age, reaching a maximum of 3–7 min in week 4 or 6 (depending on isolate) but subsequently declined to 2–4 min in week 10. By the time the IJ were becoming more readily activated in weeks 6–8, 75% of the lipid reserves had been depleted, and IJ had started to die. This greater propensity to become active with age may represent a switch to risk-taking behaviour in the face of impending starvation.

  • Phased infectivity in Heterorhabditis Megidis: the effects of infection density in the parental host and filial generation
    International journal for parasitology, 2003
    Co-Authors: Jonathan J. Ryder, Christine T. Griffin
    Abstract:

    Entomopathogenic nematodes can develop through two or more generations in the cadavers of killed insect hosts. Non-feeding infective juveniles from each generation emerge and may spend prolonged periods searching for a new host. The infectivity of the infective juveniles of Heterorhabditis Megidis varies with time after emergence and may not reach a maximum until several weeks have passed. 'Phased infectivity' hypotheses propose that this pattern is adaptive, tending to reduce competition in new hosts. Here we provide further evidence that infectivity is phased in H. Megidis. In addition, we show that the basic pattern is modified by infection density in the parental host and by filial generation. Two general patterns were observed: first, infective juveniles that developed under the least crowded conditions (F(1) infective juveniles produced in hosts infected with 16 parent nematodes) reached maximum infectivity after only 15 days, compared to 27 or 39 days for infective juveniles that developed under more crowded conditions (F(1) produced in hosts infected with 103 or 424 parent nematodes or F(2) infective juveniles). Second, infective juveniles had lower infectivity overall when produced under the most crowded conditions (F(2) versus F(1); highest versus lowest infection density). We propose that while lower overall infectivity is a necessary consequence of limited resource availability during infective juvenile development, the difference in the timing of peak infectivity reflects a shift in the fitness gains associated with being maximally infective either 'early' or 'late'. F(1) infective juveniles emerge several days before F(2) infective juveniles, and we suggest that filial generation and infection density in the parental host function as indicators of the potential risk of competition within new hosts.

Ted C. J. Turlings - One of the best experts on this subject based on the ideXlab platform.

  • Diffusion of the maize root signal (E)-β-caryophyllene in soils of different textures and the effects on the migration of the entomopathogenic nematode Heterorhabditis Megidis
    Rhizosphere, 2017
    Co-Authors: M Xavier Chiriboga, Raquel Campos-herrera, Geoffrey Jaffuel, Gregory Röder, Ted C. J. Turlings
    Abstract:

    Abstract Maize roots respond to feeding by larvae of the beetle Diabrotica virgifera virgifera by releasing ( E )-β-caryophyllene ( E βc). This insect-induced root volatile attracts entomopathogenic nematodes (EPN) and thereby helps to protect the roots against herbivore damage. Previous studies suggest that diffusion of E βc occurs through the gaseous rather than the aqueous phase in sand and its diffusion is best at low levels of humidity. However, it remains largely unknown how E βc diffuses in typical natural and agricultural soils. To fully understand the function and efficiency of root-produced E βc as a belowground signal it is important to know how it spreads in real soils and how soil properties affect its diffusion. Using gas chromatography-mass spectrometry analyses, the diffusion of two doses of synthetic E βc (200 ng and 20,000 ng) injected in sand was compared with the diffusion of E βc injected in clay, clay-loam and sandy-loam soils, at 3 moisture levels (5, 10 and 20% water), and at two distances (5 and 10 cm) from the E βc injection point. The diffusion of the compound was measured with a Solid Phase Micro Extraction (SPME) fiber every 30 minutes over a period of 9 hours. We found that, in contrast to the pattern observed for pure sand, E βc diffused best when humidity was high in the three agricultural soils. In subsequent experiments we used glass-trays to create two types of mesocosms to assess the effect of synthetic or root-produced Eβc on the dispersal of the EPN Heterorhabditis Megidis and its infection of sentinel hosts in the trays. The presence of synthetic E βc did not affect the ability of H. Megidis to infect the sentinel host. However, under the test conditions, E βc released from maize roots influenced the migration behaviour of H. Megidis depending on soil type. The results suggest that D. virgifera -damaged maize plants may recruit H. Megidis more efficiently in clay loam soils than in other types of soil. These new insights into the diffusion dynamics and attraction efficiency of the root-produced signal E βc may help efforts to develop novel strategies for the sustainable management of the maize pest D. virgifera .

  • Systemic root signalling in a belowground, volatile-mediated tritrophic interaction.
    Plant cell & environment, 2011
    Co-Authors: Ivan Hiltpold, Matthias Erb, Christelle A. M. Robert, Ted C. J. Turlings
    Abstract:

    Plants attacked by leaf herbivores release volatile organic compounds (VOCs) both locally from the wounded site and systemically from non-attacked tissues. These volatiles serve as attractants for predators and parasitoids. This phenomenon is well described for plant leaves, but systemic induction of VOCs in the roots has remained unstudied. We assessed the spatial and temporal activation of the synthesis and release of (E)-β-caryophyllene (EβC) in maize roots upon feeding by larvae of Diabrotica virgifera virgifera, as well as the importance of systemically produced EβC for the attraction of the entomopathogenic nematode Heterorhabditis Megidis. The production of EβC was found to be significantly stronger at the site of attack than in non-attacked tissues. A weak, but significant, increase in transcriptional activity of the EβC synthase gene tps23 and a corresponding increase in EβC content were observed in the roots above the feeding site and in adjacent roots, demonstrating for the first time that herbivory triggers systemic production of a volatile within root systems. In belowground olfactometers, the nematodes were significantly more attracted towards local feeding sites than systemically induced roots. The possible advantages and disadvantages of systemic volatile signalling in roots are discussed.

  • How maize root volatiles affect the efficacy of entomopathogenic nematodes in controlling the western corn rootworm?
    Chemoecology, 2010
    Co-Authors: Ivan Hiltpold, Ulrich Kuhlmann, Stefan Toepfer, Ted C. J. Turlings
    Abstract:

    Because the ferocious maize pest Diabrotica virgifera virgifera LeConte can adapt to all currently used control strategies, focus has turned to the development of novel, more sustainable control methods, such as biological control using entomopathogenic nematodes (EPN). A good understanding of the biology and behaviour of these potential control agents is essential for their successful deployment. Root systems of many maize varieties emit ( E )-β-caryophyllene (EβC) in response to feeding by larvae of the beetle D. v. virgifera . This sesquiterpene has been shown to attract certain species of EPN, thereby enhancing their control potential. In this study, we tested the effect of this root-produced volatile on the field efficacy of the three EPN Heterorhabditis bacteriophora, Heterorhabditis Megidis and Steinernema feltiae against D. v. virgifera larvae in southern Hungary. By comparing beetle emergence and root damage for two maize varieties, one that emits EβC and one that does not, it was found that root protection by H. Megidis and S. feltiae was higher on the emitting variety, but this was not the case for H. bacteriophora . Overall, all three nematode species showed good control potential. We conclude that, if properly applied and in combination with the right maize variety, the release of these nematodes can be as effective as other control methods.

  • Belowground Chemical Signaling in Maize: When Simplicity Rhymes with Efficiency
    Journal of Chemical Ecology, 2008
    Co-Authors: Ivan Hiltpold, Ted C. J. Turlings
    Abstract:

    Maize roots respond to feeding by larvae of the beetle Diabrotica virgifera virgifera by releasing ( E )-β-caryophyllene. This sesquiterpene, which is not found in healthy maize roots, attracts the entomopathogenic nematode Heterorhabditis Megidis . In sharp contrast to the emission of virtually only this single compound by damaged roots, maize leaves emit a blend of numerous volatile organic compounds in response to herbivory. To try to explain this difference between roots and leaves, we studied the diffusion properties of various maize volatiles in sand and soil. The best diffusing compounds were found to be terpenes. Only one other sesquiterpene known for maize, α-copaene, diffused better than ( E )-β-caryophyllene, but biosynthesis of the former is far more costly for the plant than the latter. The diffusion of ( E )-β-caryophyllene occurs through the gaseous rather than the aqueous phase, as it was found to diffuse faster and further at low moisture level. However, a water layer is needed to prevent complete loss through vertical diffusion, as was found for totally dry sand. Hence, it appears that maize has adapted to emit a readily diffusing and cost-effective belowground signal from its insect-damaged roots.

  • Simultaneous feeding by aboveground and belowground herbivores attenuates plant-mediated attraction of their respective natural enemies.
    Ecology letters, 2007
    Co-Authors: Sergio Rasmann, Ted C. J. Turlings
    Abstract:

    Herbivore-damaged plants emit volatile organic compounds that attract natural enemies of the herbivores. This form of indirect plant defence occurs aboveground as well as belowground, but it remains unclear how simultaneous feeding by different herbivores attacking leaves and roots may affect the production of the respective defence signals. We employed a setup that combines trapping of volatile organic signals and simultaneous measurements of the attractiveness of these signals to above and belowground natural enemies. Young maize plants were infested with either the foliar herbivore Spodoptera littoralis, the root herbivore Diabrotica virgifera virgifera, or with both these important pest insects. The parasitic wasp Cotesia marginiventris and the entomopathogenic nematode Heterorhabditis Megidis were strongly attracted if their respective host was feeding on a plant, but this attraction was significantly reduced if both herbivores were on a plant. The emission of the principal root attractant was indeed reduced due to double infestation, but this was not evident for the leaf volatiles. The parasitoid showed an ability to learn the differences in odour emissions and increased its response to the odour of a doubly infested plant after experiencing this odour during an encounter with hosts. This first study to measure effects of belowground herbivory on aboveground tritrophic signalling and vice-versa reemphasizes the important role of plants in bridging interactions between spatially distinct components of the ecosystem.

Martin J. Downes - One of the best experts on this subject based on the ideXlab platform.

  • Biological control of black vine weevil Otiorhynchus sulcatus in Ireland using Heterorhabditis Megidis
    Biological Control, 2007
    Co-Authors: Theodora Lola-luz, Martin J. Downes
    Abstract:

    Abstract Heterorhabditis Megidis (UK211) was applied against black vine weevil (BVW, Otiorhynchus sulcatus ) in potted plants in a polyethylene (2002) or glasshouse (2003) and in field planted strawberries (2003). Both potted and field strawberries were artificially infested with BVW larvae. In a 2002 pot planting in the polyethylene house, a single drench application of 25,000 H. Megidis infective juveniles per plant in 50 ml of water in mid September, reduced the number of BVW larvae to 1.8/20 plants. A second application in early October gave a reduction of 0.2/20 plants and in the third application, the following March no live weevils were recovered, compared to the control which had 8.2 larvae/20 plants. In a 2003 pot planting in a glasshouse, similar treatments gave a reduction of 5.2, 5.4 and 0.8 larvae/20 plants, respectively, compared to the control where 26.2 larvae/20 plants were recovered. In an artificially, BVW infested field trial, similar treatments gave a reduction to 2.2 larvae/20 plants in the single September treatment, and 2 larvae/20 plants in the single October treatment. The double (September and October) application reduced BVW larvae further to 1.6/20 plants and the triple (September, October and April) application to 0.4 larvae/20 plants, compared to the control where four larvae corresponded to every 20 plants. There was, therefore, little difference between the single and double autumn treatments indoors or in the field, and it mattered little whether the single application in the field was made in September or October under the conditions of 2003. Early spring application gave a significant reduction in BVW in each of the three experiments.

  • Control of Black Vine Weevil larvae Otiorhynchus sulcatus (Fabricius) (Coleoptera:Curculionidae) in grow bags outdoors with nematodes
    Agricultural and Forest Entomology, 2005
    Co-Authors: Theodora Lola-luz, Martin J. Downes, Richard Dunne
    Abstract:

    1 Outdoor trials were carried out during 2001–02 on strawberries grown in commercial growing bags naturally infested with black vine weevil larvae (BVW) Otiorhynchus sulcatus in Co. Wexford, Ireland. 2 The two nematode isolates used in these trials were Heterorhabditis Megidis (UK211) and Heterorhabditis downesi (K122), both laboratory cultured. Growing bags received nematodes either once (May 2001), twice (May and October 2001) or three times (May, October 2001 and May 2002). Ten days after each application date, nine blocks (of the total 27) were randomly selected, destructively assessed and discarded. 3 The single application (May 2001) resulted in a mortality of black vine weevil larvae, of 93.4% with H. Megidis and 51.3% with H. downesi, compared with the control treatment at that date. Respective figures after the double application (May 2001 and October 2001) were 78.9 and 77.6% and after the triple application (May 2001, October 2001 and May 2002) the figures were 93.7 and 88.1%. 4 Results from these trials clearly indicate that entomopathogenic nematodes are good alternatives to chemical control of the black vine weevil on strawberries grown in growing bags in Ireland.

  • Effect of Timber Condition on Parasitization of Pine Weevil ( Hylobius abietis L.) Larvae by Entomopathogenic Nematodes under Laboratory Conditions
    Biocontrol Science and Technology, 2002
    Co-Authors: Ignacio Armendáriz, Martin J. Downes, Christine T. Griffin
    Abstract:

    The large pine weevil ( Hylobius abietis L.) is one of the most important pests in coniferous reforestation in Europe. Larvae develop in the stumps of recently felled trees; the emerging adults feed on the bark of seedlings and may kill them. The ability of the entomopathogenic nematodes Heterorhabditis Megidis and Steinernema carpocapsae to invade pine weevil larvae in Sitka spruce ( Picea sitchensis ) buried in moist sand was evaluated. Overall, four times as many H. Megidis as S. carpocapsae invaded pine weevil larvae. The two species of nematode differed in their response to timber condition. The number of S. carpocapsae invading pine weevil larvae was twice as high in billets inoculated with the wood-rotting fungus Phlebiopsis gigantea as in fresh timber, while the number of H. Megidis invading was reduced by 25%. Invasion into non-feeding insects (larvae of the wax moth Galleria mellonella ) contained in timber disks was also affected by timber quality, indicating that nematode behaviour was affecte...

  • Application of the most probable number method to estimations of entomopathogenic nematode populations in soil
    Annals of Applied Biology, 1997
    Co-Authors: Birgit Hass, Christine T. Griffin, John G. Keating, Martin J. Downes
    Abstract:

    The calculation of most probable numbers (mpn) was used for the estimation of numbers of infective entomopathogenic nematodes in soil. The mpn concept was first introduced in bacteriology as a means of estimating numbers of organisms in a substrate without a direct count, in cases where direct enumeration could not be applied. In the work reported here, soil samples infested with infective juveniles (IJs) of Heterorhabditis Megidis (isolate HF85) were diluted with uninfested soil and the diluted soils were baited with mealworm larvae (Tenebrio molitor). The mpn of infective units of IJs in the undiluted soil was calculated. The mpn calculation was found to be applicable to entomopathogenic nematodes in soil under particular conditions. It could be successfully applied to data for the response of soil units but not to the data based on the response of individual insects, as the latter did not confirm to a Poisson series. The calculated mpn represented between 2.9 and 7.1% of the initial inoculum of IJs. It was suggested that IJs might act as a group in infecting an insect host. Using the data for Tenebrio mortality on parasitisation, the mpn based on quantal response of the mealworms would therefore not give the true density of IJs in the soil sample but the effective density, or the quantity of infective units. Although the biological significance of the infective unit needs further clarification, mpn was found to be a useful parameter for use in comparative experiments.

Ulrich Kuhlmann - One of the best experts on this subject based on the ideXlab platform.

  • Influence of soil on the efficacy of entomopathogenic nematodes in reducing Diabrotica virgifera virgifera in maize
    Journal of Pest Science, 2010
    Co-Authors: Stefan Toepfer, B. Kurtz, Ulrich Kuhlmann
    Abstract:

    The use of entomopathogenic nematodes is one potential non-chemical approach to control the larvae of the invasive western corn rootworm ( Diabrotica virgifera virgifera LeConte, Coleoptera: Chrysomelidae) in Europe. This study investigated the efficacy of Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), Heterorhabditis Megidis Poinar, Jackson and Klein (Rh., Heterorhabditidae) and Steinernema feltiae Filipjev (Rh., Steinernematidae) in reducing D. v. virgifera as a function of soil characteristics. A field experiment was repeated four times in southern Hungary using artificially infested maize plants potted into three different soils. Sleeve gauze cages were used to assess the number of emerging adult D. v. virgifera from the treatments and untreated controls. Results indicate that nematodes have the potential to reduce D. v. virgifera larvae in most soils; however, their efficacy can be higher in maize fields with heavy clay or silty clay soils than in sandy soils, which is in contrast to the common assumption that nematodes perform better in sandy soils than in heavy soils.

  • How maize root volatiles affect the efficacy of entomopathogenic nematodes in controlling the western corn rootworm?
    Chemoecology, 2010
    Co-Authors: Ivan Hiltpold, Ulrich Kuhlmann, Stefan Toepfer, Ted C. J. Turlings
    Abstract:

    Because the ferocious maize pest Diabrotica virgifera virgifera LeConte can adapt to all currently used control strategies, focus has turned to the development of novel, more sustainable control methods, such as biological control using entomopathogenic nematodes (EPN). A good understanding of the biology and behaviour of these potential control agents is essential for their successful deployment. Root systems of many maize varieties emit ( E )-β-caryophyllene (EβC) in response to feeding by larvae of the beetle D. v. virgifera . This sesquiterpene has been shown to attract certain species of EPN, thereby enhancing their control potential. In this study, we tested the effect of this root-produced volatile on the field efficacy of the three EPN Heterorhabditis bacteriophora, Heterorhabditis Megidis and Steinernema feltiae against D. v. virgifera larvae in southern Hungary. By comparing beetle emergence and root damage for two maize varieties, one that emits EβC and one that does not, it was found that root protection by H. Megidis and S. feltiae was higher on the emitting variety, but this was not the case for H. bacteriophora . Overall, all three nematode species showed good control potential. We conclude that, if properly applied and in combination with the right maize variety, the release of these nematodes can be as effective as other control methods.

  • Assessment of establishment and persistence of entomopathogenic nematodes for biological control of western corn rootworm
    Journal of Applied Entomology, 2007
    Co-Authors: B. Kurtz, Ralf-udo Ehlers, Stefan Toepfer, Ulrich Kuhlmann
    Abstract:

    The use of entomopathogenic nematodes (EPN) is potentially one ecological approach to control the invasive alien western corn rootworm (Diabrotica virgifera virgifera LeConte, Col., Chrysomelidae) in Europe. This study investigated the establishment and the short- and long-term persistence of Heterorhabditis bacteriophora Poinar (Rhabditida: Heterorhabditidae), Heterorhabditis Megidis Poinar, Jackson and Klein (Rh., Heterorhabditidae) and Steinernema feltiae Filipjev (Rh., Steinernematidae) in three maize fields in southern Hungary, using the insect-baiting technique. All three EPN species equally established and persisted in maize fields. The timing of application (April or June) did not influence the establishment of EPN species. EPNs persisted for 2-5 months, i.e. they survived up to and throughout D. v. virgifera larval occurrence in the soil. Results demonstrate that D. v. virgifera larvae can potentially be controlled by EPNs during the same year of EPN application but no long-term control effect is expected under intensive maize cultivation practices.

P.h. Smits - One of the best experts on this subject based on the ideXlab platform.

  • Behavioural response of Heterorhabditis Megidis towards plant roots and insect larvae
    BioControl, 2002
    Co-Authors: M.i.c. Boff, R.h.w.m. Van Tol, P.h. Smits
    Abstract:

    The behavioural response of infective juveniles (IJs) of Heterorhabditis Megidis (strain NLH-E87.3) to cues from roots of strawberry ( Fragaria x ananassa Duch.), thuja ( Thuja occidentalis L.) and to larvae of the black vine weevil, Otiorhynchus sulcatus , was studied. Choice assays were conducted in an Y-tube olfactometer filled with moist sand. Infective juveniles were activated by the presence of intact roots of both strawberry and thuja plants. Some nematodes aggregated in the compartments with roots but most moved away from the roots to the opposite side. Given a choice, IJs showed a preference for strawberry roots above O. sulcatus larvae. No difference in preference was observed between thuja roots and O. sulcatus larvae. The combination of strawberry roots with vine weevil larvae was preferred above roots alone. In the assays with thuja roots and larvae versus thuja roots alone, however, IJs were stimulated to move but showed preference for the opposite compartment away from the arms with roots and larvae. Nematodes responded differently to mechanically damaged roots as opposed to roots damaged by vine weevil larvae. In assays with damaged thuja roots, IJs were most attracted by the roots damaged by larvae, whereas in the strawberry assays IJs showed a clear preference for the mechanically damaged roots. When challenged with a choice between strawberry and thuja roots, IJs moved preferentially to strawberry than to thuja roots. A preference for the combination of strawberry roots plus larvae over the thuja roots plus larvae was also observed.

  • Plants protect their roots by alerting the enemies of grubs
    Ecology Letters, 2001
    Co-Authors: R.w.h.m. Van Tol, M.i.c. Boff, A.t.c. Van Der Sommen, J. Van Bezooijen, Maurice W. Sabelis, P.h. Smits
    Abstract:

    Plant roots in the soil are under attack from many soil organisms. Although many ecologists are aware of the presence and importance of natural enemies in the soil that protect the plants from herbivores, the existence and nature of tritrophic interactions are poorly understood. So far, attention has focused on how plants protect their aboveground parts against herbivorous arthropods, either directly or indirectly (i.e. by getting help from the herbivore’s enemies). This article is the first in showing that indirect plant defences also operate underground. We show that the roots of a coniferous plant (Thuja occidentalis) release chemicals upon attack by weevil larvae (Otiorhynchus sulcatus) and that these chemicals thereby attract parasitic nematodes (Heterorhabditis Megidis).

  • Host influences on the pathogenicity of Heterorhabditis Megidis
    BioControl, 2001
    Co-Authors: M.i.c. Boff, G.l. Wiegers, P.h. Smits
    Abstract:

    The infectivity of infective juveniles(IJs) of Heterorhabditis Megidis (strain NLH-E87.3) produced on small, medium and large larvae of Galleria mellonella , and on medium and largelarvae of Otiorhynchus sulcatus was tested underlaboratory conditions against G. mellonella and O. sulcatus larvae. Infective juvenilesoriginating from small G. mellonella exposed toan initial dose of one IJ were more infectious thanthose from small cadavers exposed to a dose of 30 IJs.Independent of the initial inoculum size, IJs fromsmall cadavers of G. mellonella were moreinfectious than those from medium and large cadavers.At a dose of one IJ per larva, IJs originating frommedium size O. sulcatus cadavers were moreinfective against G. mellonella than against O. sulcatus larvae. Large G. mellonella larvae were less susceptible to all IJ batches thanmedium and small sized larvae.

  • Effects of Density, Age and Host Cues on the Dispersal of Heterorhabditis Megidis
    Biocontrol Science and Technology, 2001
    Co-Authors: M.i.c. Boff, P.h. Smits
    Abstract:

    Agar plate assays were used to assess the effect of density, incubation time and age of nematodes and the presence of insect hosts on the dispersal of infective juveniles (IJs) of Heterorhabditis Megidis (strain NLH-E87.3). IJs dispersed faster and further at high densities than at low densities. Dispersal was also influenced by the age of the IJs. Individuals stored for a period of 1.5 and 4.5 weeks showed to be more active than those stored for 2.5 and 3.5 weeks. The presence of a host insect enhanced the dispersion of nematodes. The increasing in the incubation period showed that IJs responded positively to host cues from Galleria mellonella but poorly to cues from Otiorhynchus sulcatus larvae.

  • Influence of Insect Larvae and Plant Roots on the Host-finding Behaviour of Heterorhabditis Megidis
    Biocontrol Science and Technology, 2001
    Co-Authors: M.i.c. Boff, G.l. Wiegers, P.h. Smits
    Abstract:

    We studied the host-finding and dispersion behaviour of Heterorhabditis Megidis (strain NLHE 87.3) in the presence of Galleria mellonella or Otiorhynchus sulcatus larvae and strawberry roots. In large Petri dishes (19 cm diameter) filled with moist sand (8% w/w), and incubated at 15°C over 24 h, infective juveniles (IJs) responded positively to the presence of G. mellonella , to roots of a single strawberry plant and to O. sulcatus larvae in direct contact with roots of a single strawberry plant. A neutral or negative response was observed when IJs were presented with only O. sulcatus larvae or a combination of several strawberry plants with O. sulcatus larvae, either in contact or not in contact with the roots. IJs responded strongly to the combination of plant roots and feeding larvae indicating that the tritrophic interaction formed by IJs - O. sulcatus larvae - strawberry plants may be an infochemical-mediated interaction.