Source of trait deterioration in entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae during in vivo culture

Abstract

The stability of traits important for biological control was studied in the entomopathogenic nematode-bacteria complexes Heterorhabditis bacteriophora and Steinernema carpocapsae. Five experimental lines of each species were subcultured for 20 serial passages in Galleria mellonella larvae to assess trait stability. Subculturing impaired performance of both H. bacteriophora and S. carpocapsae. Virulence, heat tolerance and fecundity deteriorated in all H. bacteriophora experimental lines, and four out of five experimental lines deteriorated in host-finding ability. All S. carpocapsae experimental lines deteriorated in heat tolerance and nictation, and four out of five experimental lines declined for reproductive capacity, whereas virulence declined in two experimental lines. Determination of whether trait deterioration was due to changes in nematode, bacteria, or both symbiotic partners was tested by exchanging nematodes or bacteria from control populations with nematodes or bacteria from the most deteriorated experimental lines and assessing trait recovery. The source of deterioration varied according to trait, but only the bacterial partner played a role in trait reductions for every trait and species, whereas the nematode was the main source only for S. carpocapsae nictation. These results emphasise the important role each symbiotic partner plays in the stability and expression of beneficial traits.

Entomopathogenic Nematode Application Technology

“…Trait deterioration can be genetically based (e.g., inbreeding, drift, inadvertent selection), or stem from non-genetic factors (e.g., disease or nutrition) (Chaston et al, 2011;Hopper, Roush, & Powell, 1993;Tanada & Kaya, 1993). Deterioration in EPNs has been observed under laboratory conditions for various traits such as virulence, environmental tolerance, reproductive capacity, and host-finding (Bai, Shapiro-Ilan, Gaugler, & Hopper, 2005;Bilgrami, Gaugler, Shapiro-Ilan, & Adams, 2006;Shapiro, Glazer, & Segal, 1996;Wang & Grewal, 2002). Both the nematodes and their bacterial symbionts may experience trait loss (Bilgrami et al, 2006;Wang et al, 2007).…”

“…Deterioration in EPNs has been observed under laboratory conditions for various traits such as virulence, environmental tolerance, reproductive capacity, and host-finding (Bai, Shapiro-Ilan, Gaugler, & Hopper, 2005;Bilgrami, Gaugler, Shapiro-Ilan, & Adams, 2006;Shapiro, Glazer, & Segal, 1996;Wang & Grewal, 2002). Both the nematodes and their bacterial symbionts may experience trait loss (Bilgrami et al, 2006;Wang et al, 2007). The cause of trait deterioration in EPNs (H. bacteriophora) was reported to be genetically based with inbreeding depression being the prominent issue (Adhikari et al, 2009;Bai et al, 2005;Chaston et al, 2011).…”

Entomopathogenic Nematodes in the Soil Environment: Distributions, Interactions and the Influence of Biotic and Abiotic Factors

“…Indeed, artificial rearing conditions themselves could have an important influence on the development and reproduction of EPNs, alter the dynamics involved, and select for an array of different traits from those that are important in nature. This kind of inadvertent selection has been documented for laboratory cultures of EPNs (Bilgrami, Gaugler, Shapiro-Ilan, & Adams, 2006; and could influence the establishment and persistence abilities of mass-reared nematodes when applied in the field.…”

Intraspecific variation among isolates of the entomopathogenic nematode Steinernema feltiae from Bull Island, Ireland

“…However Bai et al (2005) found that inbred lines of H. bacteriophora can prevent beneficial trait decline by causing greater mortality to host insects than foundation populations. Bilgrami et al (2006) found that the loss of virulence against G. mellonella larvae was the result of bacterial deterioration during subculturing.…”

“…Laboratory culture of EPN may have detrimental effects on laboratory populations due to, for example, selection under artificial conditions and inbreeding depression (Stuart & Gaugler, 1996;Bilgrami et al, 2006). Costa et al (2007) state that factors such as the virulence of the symbiotic bacteria, species of host used, concomitant infection with another organism, and the number of penetrated IJ, can affect the multiplication potential of EPN.…”