The influence of habitat quality on the foraging strategies of the entomopathogenic nematodes Steinernema carpocapsae and Heterorhabditis megidis

Institute of Biological and Environmental Sciences, University of Aberdeen, Cruickshank Building, Aberdeen, AB24 3UU, UK.
Parasitology (Impact Factor: 2.56). 10/2009; 137(2):303-9. DOI: 10.1017/S0031182009991326
Source: PubMed


Entomopathogenic nematodes (EPN) are soil-transmitted parasites and their foraging strategies are believed to range from 'ambush' to 'cruise' foragers. However, research on their behaviour has not considered the natural habitat of these nematodes. We hypothesized that EPN behaviour would be influenced by soil habitat quality and tested this hypothesis using 2 EPN species Steinernema carpocapsae (an 'ambusher') and Heterorhabditis megidis (a 'cruiser') in 2 contrasting habitats, sand and peat. As predicted from previous studies, in sand most S. carpocapsae remained at the point of application and showed no taxis towards hosts, but in peat S. carpocapsae dispersed much more and showed a highly significant taxis towards hosts. H. megidis dispersed well in both media, but only showed taxis towards hosts in sand. In outdoor mesocosms in which both species were applied, S. carpocapsae outcompeted H. megidis in terms of host finding in peat, whereas the opposite was true in sand. Our data suggest that these 2 EPN may be habitat specialists and highlight the difficulties of studying soil-transmitted parasites in non-soil media.

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    • "The bioassay investigating temperature response of S. carpocapsae against H. arator adults was similar but used higher nematode dose, had a longer exposure time, and used peat, a medium known to favour host finding by S. carpocapsae (Kruitbos et al., 2010). The same 3 cm diameter 6-chamber multi-well plates were used, but were filled with moist peat, a medium known to favour host finding by S. carpocapsae (Kruitbos et al., 2010). One thousand S. carpocapsae infective juveniles were added to each well, and plates were incubated for two-weeks at the appropriate temperature. "
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    ABSTRACT: The African black beetle (Heteronychus arator F.) is a pest of pastures in the North Island of New Zealand. Except during dispersal activity, adult beetles live in the soil and feed at the base of grass stems during spring and fall and to a lesser amount over-winter. Larvae develop over summer months feeding on the grass roots. We tested three life-stages of H. arator (first and third instar larvae and adults) for susceptibility to the four entomopathogenic nematode (EPN) species present in New Zealand: Steinernema carpocapsae, Steinernema feltiae, Heterorhabditis bacteriophora and Heterorhabditis zealandica. All H. arator stages were found to be susceptible to EPN, but different life-stages varied in susceptibility to EPN species. Based on our laboratory assays, we chose to target adult beetles using S. carpocapsae. We ran three field experiments, one in spring and two in fall but the EPN did not reduce beetle numbers in any experiments. Field temperatures were cool, but within the stated thermal niche breadth of S. carpocapsae for killing hosts. Sampling on nematode-treated plots revealed several susceptible lepidopteran larvae clearly infected with S. carpocapsae but no infected H. arator. We tested the hypothesis that the effective niche breadth for killing hosts may vary with host-susceptibility. We studied the temperature response of S. carpocapsae against Galleria mellonella and H. arator at 12.5, 15, 18, 20 and 25. °C. While S. carpocapsae caused significant mortality of G. mellonella at all temperatures, no H. arator mortality was seen at 12.5 or 15. °C despite using a high nematode rate and incubating for two weeks. Our data highlight the importance of testing susceptibility of different insect life stages at the temperatures likely to be encountered in the field following nematode application.
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    • "Their presence and abundance is associated with a number of biotic and abiotic soil characteristics, including soil texture, temperature and moisture (Lawrence et al., 2006), as well as a combination of additional physical, chemical and biotic conditions (Hoy et al., 2008). Applied EPNs have been found to disperse more actively in soils high in organic matter than they do in mineral soils (Kruitbos et al., 2010; MacMillan et al., 2009; Wilson et al., 2012) and their persistence is strongly correlated with high soil moisture (Grant and Villani, 2003; Jabbour and Barbercheck, 2008). The persistence of EPN populations after they have been applied as a biological insecticide also depends on the availability of invertebrate hosts within the soil environment (Susurluk and Ehlers, 2008). "
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    • "Torr et al. (2004) showed that S. carpocapsae had strong response to a wide range of vibrational cues. Recently Kruitbos et al. (2010) stated that S. carpocapsae is adapted to being active in habitats other than mineral soils (e.g., peat, leaf litter, bark or wood). Our results support this finding and also fit with the habitat preferences of this species; S. carpocapsae prefer woodlands where their soil habitats have much higher organic matter contents (Hominick, 2002). "
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