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

Abstract

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.

Pine weevils modulate defensive behaviour in response to parasites of differing virulence

“…Hypotheses concerning the adaptations of entomopathogenic nematodes frequently include members of both genera as representatives of the group (e.g. Kruitbos et al 2010). …”

Behaviour and Population Dynamics of Entomopathogenic Nematodes Following Application

“…S. carpocapsae IJs move both vertically, reaching depths of 15-20 cm in soil (Ferguson, Schroeder, & Shields, 1995) and laterally: about 4 % of S. carpocapsae IJs ("sprinters") dispersed faster than the fastest H. bacteriophora (Bal, Taylor, & Grewal, 2014). Dispersal by S. carpocapsae IJs appears to be strongly influenced by substrate, being much greater in pure peat than in pure sand (Kruitbos, Heritage, Hapca, & Wilson, 2010). In nature, IJs emerge in their thousands from the depleted natal host and should have experienced strong selection to move away from these overcrowded conditions.…”

“…EPN can disperse and find hosts in these highly organic media (Ansari & Butt, 2011;Nielsen & Lewis, 2011). Kruitbos et al (2010) compared pure sand and pure peat as media for EPN dispersal and host-finding, and found contrasting responses for two species; the ambush forager S. carpocapsae displayed host-finding behaviour in peat but not in sand, while the reverse was true for the cruise forager H. megidis. S. carpocapsae also dispersed better in peat than in sand.…”

The impact of entomopathogenic nematodes on a non-target, service-providing longhorn beetle is limited by targeted application when controlling forestry pest Hylobius abietis

“…Moreover, there is evidence to suggest that the dispersal of IJs, including those of S. carpocapsae, depends to a large degree on substrate texture (Georgis and Poinar, 1983;Molyneux and Bedding, 1984;Portillo-Aguilar et al, 1999;Jabbour and Barbercheck, 2008). In laboratory assays, S. carpocapsae IJs moved through peat soil as effectively as IJs of cruiser species Heterorhabditis megidis (Kruitbos et al, 2010) and they moved through R. bifasciatum frass as effectively as IJs of H. downesi (C. Harvey, unpublished data). Steinernema carpocapsae IJs (as well as those of S. feltiae and H. megidis) have been found to aggregate in response to vibrations (Torr et al, 2004) and frass galleries within the wood may provide routes for IJs to follow to the feeding insects at their terminus (Lindegren et al, 1981), just as plant roots can serve as routeways to host insects .…”