Effect of agitation speed on the density of bacteria Photorhabdus luminescens and the population dynamics of nematodes Heterorhabditis megidis in liquid culture

Liquid culture is the most scalable technology for the industrial production of entomopathogenic nematodes. Variability of the recovery after inoculation into cultures of Photorhabdus luminescens remains a persistent problem in the mass production of Heterorhabditis sp. In order to enhance infective juvenile (IJ) recovery and improve nematode population management, we analysed the correlation between the nematode Heterorhabditis megidis (strain KV – 136) development in liquid cultures, the density of bacteria of P. luminescens and the culture agitation speed. Analyses focused on the impact of different agitation speeds (160 rpm and 200 rpm) on the dynamics of population growth of H. megidis in liquid cultures at constant biotic and abiotic parameters (initial dose of nematodes introduced to the culture 2300 IJs/ml, temperature 25°C, the number of bacterial colonies 0.3 × 107/ml). The performed experiments showed that the agitation speed of 200 rpm favourably affected the density of bacteria of P. luminescens (24.14 × 107/ml). High density of bacteria at this agitation speed resulted in an earlier (on the fifth day of the culture) maximum increase in the number of hermaphroditic individuals (1239.6 H/ml) than in the culture at an agitation speed of 160 rpm.

Occurrence of entomopathogenic nematodes in Polish soils

ABSTRACT: Entomopathogenic nematodes ( Steinernematidaeand Heterorhabditidae) were studied in Polish soils according to the: season, habitat and altitude. In total, 167 soil samples were taken from 111 localities in Poland along north-south transect. Entomopathogenic nematodes were isolated from 53 soil samples (31.7%). Nematodes species were identified genetically from 16 samples, and in all other 37 samples nematodes were determined to the genus level. Three species of the genus Steinernema ( Steinernema kraussei, S. feltiae, S. carpocapsae) and one of the genus Heterorhabditis( Heterorhabditis megidis) were recorded. Steinernema feltiaewas the most common species. There was not a significant association between the occurrence of nematodes and season or altitude. The type of habitat significantly (P<0.05) affected the occurrence of nematodes. Nematodes were most frequent in samples collected from coniferous forests (20 findings).

The effect of initial dose on the recovery and final yields of Heterorhabditis megidis (Rhabditida: Heterorhabditidae) in larvae of the great wax moth, Galleria mellonella

The aim of this study was to determine the effect of different initial doses of the infective juveniles (IJs) (50 IJs, 200 IJs, 1000 IJs) of Heterorhabditis megidis Poinar (Rhabditida: Heterorhabditidae) strain IsM15/09 on recovery, final yields and percent final yields in larvae Galleria mellonella ( L.). Percent recovery was not directly related to initial dose. Final yields also did not change with the initial dose. However, percent yields was highly negatively correlated with initial dose of nematodes and was the highest with the 50 IJs dose. Additional point of the study was to investigate whether the nematodes are able to produce progeny from one hermaphroditic individual. The results showed that the invasive larvae resumed growth and transformed into hermaphroditic individuals that reproduced without cross-fertilisation.

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

SUMMARYEntomopathogenic 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.

Scavenging or infection? Possible host choosing by entomopathogenic nematodes

Entomopathogenic nematodes are able to survive by scavenging. We tested Steinernema feltiae, S. affine and Heterorhabditis megidis alone or in different combinations to evaluate the responses of these nematodes when dead or live Galleria mellonella larvae were offered. Steinernema feltiae and S. affine scavenged upon dead G. mellonella larvae and about 30% more dead larvae were penetrated than live ones. By contrast, H. megidis penetrated more live larvae than dead ones. When the nematode species were combined, the results varied among the combinations, but the dead larvae were always used as a host. The behaviour of natural field populations of S. feltiae and S. affine was also compared. Steinernema feltiae showed no difference between scavenging and performing 'normal infections', whereas S. affine scavenged to a reduced amount (around 60% less); this difference could be related to the particular foraging strategy of these nematodes.