|Shapiro ilan, David|
Submitted to: Nematology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/24/2006
Publication Date: 10/1/2006
Citation: Bilgrami, A.L., Gaugler, R., Shapiro Ilan, D.I., Adams, B. 2006. Source of trait deterioration in entomopathogenic nematodes heterorhabditis bacteriophora and steinernema carpocapsae during in vivo culture. Nematology. 8:397-409 Interpretive Summary: Insect-killing nematodes are naturally occurring round worms that can be used as environmentally friendly bio-insecticides. The nematodes kill insects with the help of specialized bacteria that are carried in the nematode’s gut. When these organisms are grown continuously in the laboratory or in industrial settings, beneficial characteristics can be lost due to potentially harmful genetic changes. In this study we characterized the loss of beneficial traits in two species of nematodes. We determined that loss of virulence, reproductive capacity, and heat tolerance can occur rapidly in the laboratory. We also discovered that both the bacteria and nematodes play an important role in the loss of beneficial traits. Understanding the cause of trait loss will help overcome the problem, and lead to better usage of biological pest control options such as these nematodes.
Technical Abstract: The stability of traits important for biological control was studied in the entomopathogenic nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae. Five isolines of each species were subcultured for 20 passages in Galleria mellonella larvae to assess trait stability. Subculturing impaired fitness of both the H. bacteriophora and S. carpocapsae nematode-bacteria complexes. Virulence, heat tolerance, and fecundity deteriorated in all H. bacteriophora experimental isolines, and four of five isolines deteriorated in host-finding ability. By comparison, all S. carpocapsae isolines deteriorated in heat tolerance and nictation, and four of five isolines declined for reproductive capacity, whereas virulence had a single isoline showing deterioration. The source of deterioration (nematode, bacteria, or both) varied according to trait, but only the bacterial partner played a role in fitness reductions for every trait and species, whereas the nematode was the main source only for S. carpocapsae nictation. Our results elucidate the important role each symbiotic partner plays in the stability and expression of beneficial traits.