Foraging efficacy of the entomopathogenic nematode Steinernema riobrave in different soil types from California citrus groves

et al. 2011

Laboratory experiments were conducted on the behavioral responses of five species of entomopathogenic nematodes (EPNs; Steinernema diaprepesi, Steinernema sp. glaseri-group, Steinernema riobrave, Heterorhabditis zealandica, Heterorhabditis indica) to three species of nematophagous fungi (NF; trapping fungus Arthrobotrys gephyropaga; endoparasites Myzocytium sp., Catenaria sp.). We hypothesized that EPN responses to NF and their putative semiochemicals might reflect the relative susceptibility of EPNs to particular NF species. EPN responses to "activated" NF (i.e., induced to form traps or sporangia by previous interactions with nematodes) versus controls of non-activated NF or heat-killed EPNs were compared in choice experiments on water agar in Petri dishes (dia=9 cm) and in horizontal sand columns (8 cm L×2.7 cm dia). On agar, all EPN species were attracted to all activated NF species except for S. riobrave, which was neutral. In sand, all EPN species were repelled by activated Arthrobotrys but attracted to activated Myzocytium and Catenaria, except H. indica (neutral to Myzocytium) and Steinernema sp. (neutral to Catenaria). EPN behavioral responses appeared unrelated to relative susceptibility to NF except that H. indica exhibited low susceptibility and a neutral response to Myzocytium in sand whereas the remaining EPNs were highly susceptible and attracted. These results indicate potential complexity (i.e., mixed responses, aggregation or group movement) and species specificity in the responses of EPNs to NF, demonstrate that results on agar can differ markedly from those in sand, and underline the potential importance of utilizing natural substrates to properly assess the role of semiochemicals in nematode-fungus interactions.

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Section: Discussionmentioning

confidence: 97%

Substrate modulation, group effects and the behavioral responses of entomopathogenic nematodes to nematophagous fungi

et al. 2011

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“…Soil porosity was found to be positively associated with EPN predation rates in a number of studies (Barbercheck, 1992;Barbercheck and Kaya, 1991;Campos-Herrera and Gutiérrez, 2009;Hara et al, 1991;Hazir et al, 2003;Kaspi et al, 2010;Kung et al, 1990;Liu and Berry, 1995;McCoy et al, 2003;Portillo-Aguilar et al, 1999;Rueda et al, 1993;Stuart et al, 2006;Zhang et al, 1992), and predation of DRW by EPNs during 2 years was much greater in a central ridge orchard on coarse sand than in a flatwoods orchard on finer textured, sandy loam soil (Duncan et al, 2003). In contrast, Shapiro et al (2000) demonstrated greater efficacy by two EPN species against DRW in fine textured compared to coarse textured soils at a standard water potential and speculated that greater water content might have favored EPNs in the finer soil.…”

Section: Introductionmentioning

confidence: 94%

Entomopathogenic nematodes, root weevil larvae, and dynamic interactions among soil texture, plant growth, herbivory, and predation

et al. 2012

Greenhouse experiments were conducted to assess the influence of soil texture on the persistence, efficacy and plant protection ability of entomopathogenic nematodes (EPNs) applied to control larvae of the Diaprepes root weevil (DRW), Diaprepes abbreviatus, infesting potted citrus seedlings. Seedlings were grown in pots containing either coarse sand, fine sand, or sandy loam. Three DRW larvae were added to each of 80 pots of each soil type. 24 h later, 20 pots of each soil type that had received weevil larvae were inoculated with EPN infective juveniles (IJs) of one of the following species: Steinernema diaprepesi, Steinernema riobrave and Heterorhabditis indica. Pots of each soil without EPNs were established as controls with DRW and controls without DRWs. Subsequently, pots with larvae received three additional larvae monthly, and the experiment continued for 9 months. Plant root and top weights at the end of the experiment were affected by both soil (P≤0.0001) and nematodes (P≤0.0001), and nematode species protected plants differently in different soils (interaction P≤0.0001). Soil porosity was inversely related to plant damage by DRW, whether or not EPNs were present; and porosity was directly related to the level of plant protection by EPNs. Mortality of caged sentinel weevil larvae placed in pots near the end of the experiment was highest in pots treated with S. diaprepesi. In a second, similar experiment that included an additional undescribed steinernematid of the Steinernema glaseri-group, soil type affected root damage by DRW and root protection by EPNs in the same manner as in the first experiment. Final numbers of S. diaprepesi and Steinernema sp. as measured by real-time PCR were much greater than those of S. riobrave or H. indica in all soils. Across all treatments, the number of weevil larvae in soil at the end the experiment was inversely related to soil porosity. In all soils, fewer weevil larvae survived in soil treated with S. diaprepesi or Steinernema sp. than in controls with DRW or treatments with S. riobrave or H. indica. The results of these experiments support the hypothesis that EPNs provide greater protection of seedlings against DRW larvae in coarse textured soil than in finer textured soil. However, less vigorous growth of the control without DRW seedlings in the two finer textured soils suggests that unidentified factors that stressed seedlings in those soils also impaired the ability of seedlings to tolerate weevil herbivory.

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“…Such conditions may suppress indigenous EPN populations and temporarily reduce pest control (Duncan et al, 2003aStuart et al, 2008). Moreover, the recognition of habitats favorable for EPN, directly or indirectly via food web interactions, can help determine the conditions under which EPN augmentation is profitable (Kaspi et al, 2010), or what modifications are necessary to improve pest suppression by EPNs (Lewis et al, 1998;Stuart et al, 2008).…”

Section: Introductionmentioning

confidence: 98%

“…Moreover, several species such as S. carpocapsae, S. feltiae and H. bacteriophora are so broadly distributed across different habitats that they have been described as ubiquitous (Hominick, 2002). Nevertheless, EPN spatial patterns, population density, and insecticidal efficacy vary by soil characteristics, agricultural management (Campos-Herrera et al, 2008;Kaspi et al, 2010;Lawrence et al, 2006), prey availability, soil moisture and soil temperature Mráček et al, 2005;Pů ža and Mráček, 2005), as well as pressure from competitors, predators and pathogens Glazer, 2002). Consequently, understanding the role of native and/or augmented EPN in pest suppression requires knowledge about the behavior of food webs in diverse habitats (Strong, 2002).…”

Section: Introductionmentioning

confidence: 98%

Entomopathogenic nematodes, phoretic Paenibacillus spp., and the use of real time quantitative PCR to explore soil food webs in Florida citrus groves

et al. 2011