Entomopathogenic Nematodes Steinernema Feltiae Research Articles

Potent Ant Deterrents Emitted from Nematode-Infected Insect Cadavers

Most known species of entomopathogenic nematodes (EPNs) are generalist obligate parasites of insects. They kill their hosts within days after infection and mortality is mainly caused by toxins produced by bacteria that co-infect the hosts and serve as food for the nematodes. EPNs can infect a very broad spectrum of insects and these insects can therefore be expected to have evolved strategies to avoid infection. Indeed, ants are known to avoid feeding on EPN-infected insect cadavers, most likely because they are repelled by semiochemicals that emanate from the cadavers. The source and nature of these repellents are so far unknown. In a series of behavioral and chemical analytical experiments we identified hexadecanal and 2-heptadecanone as two compounds that are emitted by insect larva that are infected by the EPN Steinernema feltiae, but not by uninfected larvae. When spiking honey water with the two semiochemicals, they were confirmed to be highly deterrent to the ant Lasius niger. The environmentally benign hexadecanal and 2-heptadecanone could be employed to ward off ants and possibly other pests. Additional experiments are needed to fully determine their application potential.

Potent Ant Repellents Emitted from Nematode-Infected Insect Cadavers

Most known species of entomopathogenic nematodes (EPNs) are generalist obligate parasites of insects. They kill their hosts within days after infection and mortality is mainly caused by toxins produced by bacteria that co-infect the hosts and serve as food for the nematodes. For the successful infection and preservation of the cadaver the nematodes rely heavily on the bacteria, which, in turn, benefit from the symbiotic association via the effective transmission by the EPN. The bacteria also help to protect the cadavers, which may include the production of repellent compounds. Indeed, ants are known to avoid feeding on EPN-infected insect cadavers, most likely because they are repelled by volatiles that emanate from the cadavers [9-11]. Determining the source and nature of these repellents has proven to be a major challenge. Here, in a series of behavioral and chemical analytical experiments, we identified 2-heptadecanone and 2-hexadecanal as two volatile compounds that are emitted in substantial amounts by insect larvae infected by the EPN Steinernema feltiae, but not by uninfected larvae. When spiking sugar water with the two volatiles, they were confirmed to be highly repellent to the ant Lasius niger. Most probably, the mutualistic bacterium Xenorhabdus bovienii is the source of these repellents, and preliminary assays suggest they also repel other arthropods, such as mosquitoes. If so, the environmentally benign 2-heptadecanone and 2-hexadecanal could potentially be employed to ward off important pests.

Effect of contaminated soil on multitrophic interactions in a terrestrial system

The effect of contaminated soil on multitrophic interactions in a terrestrial system was studied in a mesocosm experiment with European beech, larvae of summer chafer, and entomopathogenic nematodes (EPN). Beech seedlings were grown in non-contaminated forest and garden soil contaminated with potential toxic elements Cd, Pb and Zn, and in the absence/presence of summer chafer larvae. Root morphology and ectomycorrhizal communities were analysed. Volatile organic compounds (VOC) emitted from beech roots were investigated by GC-MS. Humulene, β-caryophyllene, borneol and camphor were selected for chemotaxis assay with EPN Steinernema feltiae, S. carpocapsae and Heterorhabditis bacteriophora. Increased root tip density was observed as a response to soil contamination and root herbivory. Soil contamination decreased ectomycorrhizal species richness. Analyses of VOC yielded 14 different compounds. Results showed that the least mobile nematode species towards the VOC tested was S. feltiae. β-caryophyllene was an attractant for S. carpocapsae and humulene a weak attractant for H. bacteriophora. Beech roots emitted VOC that affected movement of EPN. β-caryophyllene was detected in beech roots regardless of treatment, indicating that VOC that affect movement of EPN are emitted even in the absence of direct root herbivore attack.

Responses of entomopathogenic nematode, Steinernema feltiae to cucurbitacin-containing Nemafric-BL phytonematicide

Cucurbitacin-containing phytonematicides have potent nematicidal effects on plant-parasitic nematodes, but their effects on entomopathogenic nematodes (EPN) are unknown. The objective of our study was to determine the effects of cucurbitacin-containing Nemafric-BL phytonematicide on the viability (survival and mortality) of the EPN Steinernema feltiae. Infective juveniles (IJ) of S. feltiae were exposed to dilutions of the phytonematicide at 0.0, 1.5, 3.0, 4.5, 6.0, 7.5 and 9.0% for 24, 48 and 72 h. Survival and mortality of IJ over increasing concentrations of the test phytonematicide exhibited negative and positive quadratic relations, respectively. Since y-intercepts in mortality curves were higher than zero, observations were adjusted for corrected mortality and subjected to lines of the best fit. Corrected IJ mortality over increasing phytonematicide concentrations exhibited positive quadratic relations, with y-intercept being equivalent to zero. Infective juvenile survival and corrected mortality over increasing Nemafric-BL phytonematicide concentrations exhibited quadratic relations, with survival relations explained by 93, 93 and 90% COD at 24, 48 and 72 h exposure durations, respectively. The optimum concentration for corrected IJ mortality and minimum concentration for IJ survival were almost equivalent. In conclusion, within the tested concentration ranges, the sensitivity of S. feltiae IJ to the phytonematicides was low as shown by the gradual increase in corrected IJ mortality and the gradual decrease in IJ survival, without intersection of the two curves.

Life history trait analysis of the entomopathogenic nematode Steinernema feltiae provides the basis for prediction of dauer juvenile yields in monoxenic liquid culture.

Entomopathogenic nematodes (Steinernema spp.) are used in integrated pest management to control insect pests in cryptic environments. The nematodes are mass produced in monoxenic liquid culture with their symbiotic bacteria Xenorhabdus spp. For a better understanding of nematode population dynamics, the life history traits (LHTs) of the entomopathogenic nematode Steinernema feltiae were assessed at 25°C by observing single pairs of male and female nematodes using a hanging drop technique. To investigate the influence of different food supplies on nematode reproduction, the LHTs were assessed with a daily supply of 5×, 10× and 20×10(9)cellsml(-1) of the nematode's bacterial symbiont Xenorhabdus bovienii in semi-solid nematode growth gelrite (NGG) medium. Increasing bacterial density had a significant positive influence on the average number of offspring produced, which ranged from 359 to 813 per female. The intrinsic rate of natural increase r m, which ranges from 1.10 to 1.19day(-1), was neither influenced by the bacterial density, nor was the mean generation time T (5.12-5.25days) and population doubling time (PDT) (0.64-0.59days). The average lifespan of reproductive females, which ranged from 6.7 to 7.3days, was positively correlated with bacterial density. A positive correlation between female body volume and bacterial density was recorded (R=0.67) as well as a significant positive correlation between female body size and offspring production (R=0.89) in hanging drops. Whether these data can be used to predict nematode yields in liquid culture was tested. The total female body volume calculated as the average female body volume × total number of parental females per millilitre 3days after nematode inoculation was positively correlated (R=0.72) with nematode yields. The total female body volume on process day 3 is thus a good indicator for the estimation of nematode yield at the end of the process (12-15days post dauer juvenile (DJ) inoculation) in both Erlenmeyer flasks and bioreactors. With a mean deviation of 9467DJsml(-1), the error resembles approximately 5% of the final DJ yields.

Hybridisation and selective breeding for improvement of low temperature activity of the entomopathogenic nematode Steinernema feltiae

Steinernema feltiae is used to control overwintering larvae of the codling moth Cydia pomonella L. Application is in autumn when efficacy can be limited by low temperature. The objective of this study was to screen for low temperature activity among wild type populations of S. feltiae, hybridise most active strains and further improve low temperature activity by subjection of a hybrid strain to selective breeding. Significant variation was recorded among 22 S. feltiae strains. The temperature at which 50 % (AT50) and 10 % (AT10) of the dauer juveniles (DJs) were active ranged between 2.9 to 5.8 °C and 0.95 to 3.5 °C, respectively. The mean AT50 of 22 S. feltiae strains was 3.83 °C. The five most active strains were crossed. The hybrid strain HYB01 was more active at low temperature than parental and other hybrid strains with an AT50 of 0.52 °C and an AT10 of 0.09 °C. The tolerance was lost after few reproductive cycles in the insect Galleria mellonella, but was recovered after seven selection cycles with exposure to lowering temperatures. The heritability for the low temperature activity was calculated at h 2 = 0.45. Negative trade-off effects on virulence against C. pomonella and reproduction on the same insect were not reported. The most virulent strain was a commercial strain with an LD50 of 30.2 at 8 °C and 37.2 DJs per cocooned instar at 15 °C, followed by the selected hybrid with 48.1 and 47.4 DJs, respectively. Offspring production reached 15.000 DJs per instar at 8 °C and was only half at 15 °C. The results well document the potential of a breeding programme for enhancement of the activity of S. feltiae at lower temperature with the objective to improve the control potential of overwintering codling moth C. pomonella.

Erratum to: Central European Journal of Biology, Volume 7, Issue 1

Abstract Paper by Hussein et al. “Effectiveness of the entomopathogenic nematode Steinernema feltiae in agar gel formulations against larvae of the Colarado potato beetle, Leptinotarsa decemlineata (Say.) (Coleoptera: Chrysomelidae)” in Volume 7, Issue 1, 77–82 9 / February 2012; DOI: 10.2478/s11535-011-0090-0 contains an error in the title. The correct title is presented below.

Genetic improvement of the desiccation tolerance and host-seeking ability of the entomopathogenic nematode Steinernema feltiae

Entomopathogenic nematodes (EPNs) from the genus Steinernema (Steinernematidae) are used for biological control of insect pests. The infective stages of these nematodes are intolerant of extreme environmental conditions. Genetic improvement has been suggested as an approach for improving their ability to overcome these limitations. In this study, we bred a heterogeneous population of the EPN Steinernema feltiae Filipjev for desiccation tolerance (both rapid and slow) and enhanced host-seeking ability. We selected for tolerance of rapid desiccation by exposing infective juveniles (IJs) to ambient conditions (22–25°C; 50–65% r.h.) for 100 min. A survival rate of 80–90% was reached after ten selection cycles. To select for tolerance of slow desiccation, we exposed IJs to 97% r.h. for 72 h, followed by further exposure to 85% r.h. for an additional 72 h. A high survival rate (>85%) was obtained after 20 selection cycles. We selected for enhanced downward dispersal by forcing IJs to move through a sand column to reach larvae of last-instar Galleria mellonella placed at the bottom of the column. After 25 selection cycles, the majority (>75%) of these nematodes were found at the layer close to the insects. No reduction in fitness was detected in the selected populations. Nevertheless, the nematode population selected for enhanced downward dispersal displayed significantly higher infectivity than the foundation population. The population selected for slow desiccation was more tolerant of heat stress than the foundation population. These findings establish the basis for improvement of this nematode for use as a biological control agent under field conditions.

Combining the botanical insecticides NSK extract, NeemAzal T 5%, Neemix 4.5% and the entomopathogenic nematode Steinernema feltiae Cross N 33 to control the peach fruit fly, Bactrocera zonata (Saunders)

Botanical insecticides based on azadirachtin and the entomopathogenic nematode Steinernema feltiae were evaluated for their control of the peach fruit fly, <i>Bactrocera zonata</i>. Laboratory bioassays determined the potential of combinations between the biological control agent S. feltiae and the botanical insecticides NSK, NeemAzal T 5%, Neemix 4.5% against 3rd instar larvae of <i>B. zonata</i>. Of 25 treatment combinations between azadirachtin from NSK extract and <i>S. feltiae</i>, 18 gave synergistic responses, 4 were additive, none antagonistic and 3 without any response. The same number of combinations with NeemAzal T 5% showed 19 synergistic responses, 1 additive, none antagonistic and 5 without any response. Combinations of Neemix 4.5% and S. feltiae showed 11 synergistic responses, 5 additive, 3 antagonistic and 6 without any response. The combined use of botanical insecticides based on azadirachtin, especially NSK extract and NeemAzal T 5%, with the entomopathogenic nematode <i>S. feltiae</i> may offer an integrated approach to increase the efficacy of control of the peach fruit fly, <i>B. zonata</i>, by entomopathogenic nematodes.

Entomopathogenic nematodes for the biological control of crustaceans (Porcellio scaber Latr.) and millipedes (Blaniulus guttulatus Bosc.) in greenhouse

The effect of entomopathogenic nematodesSteinernema feltiae applied in dose 80 nematodes/cm2 of soil on non-insect pests: crustaceans and millipedes were assessed in greenhouse. No differences were got between number of plants damaged by these pests when nematodes were added to the soil 8 days after vegetables sowing. When the plants were sown after nematodes application number of seedlings damaged were two in case of millipedes, or three in case of crustaceans, times less than in the check withoutS. feltiae. About 50% and higher cumulative mortality of these pests was observed between 2–8 week after nematodes application. The nematodes multiplied well in the millipedes and crustaceans bodies.