A comparative analysis of entomoparasitic nematodes <i>Heterorhabditis bacteriophora</i> and <i>Steinernema carpocapsae</i>

Abstract

Heterorhabditis bacteriophora and Steinernema carpocapsae are microscopic entomoparasitic nematodes (EPNs) that are attractive, organic alternatives for controlling a wide range of crop insect pests. EPNs evolved with parasitic adaptations that enable them to "feast" upon insect hosts. The infective juvenile, a non-feeding, developmentally arrested nematode stage, is destined to seek out insect hosts and initiates parasitism. After an insect host is located, EPNs enter the insect body through natural openings or by cuticle penetration. Upon access to the insect hemolymph, bacterial symbionts (Photorhabdus luminescens for H. bacteriophora and Xenorhabdus nematophila for S. carpocapsae) are regurgitated from the nematode gut and rapidly proliferate. During population growth, bacterial symbionts secrete numerous toxins and degradative enzymes that exterminate and bioconvert the host insect. During development and reproduction, EPNs obtain their nutrition by feeding upon both the bioconverted host and proliferated symbiont. Throughout the EPN life cycle, similar characteristics are seen. In general, EPNs are analogous to each other by the fact that their life cycle consists of five stages of development. Furthermore, reproduction is much more complex and varies between genera and species. In other words, infective juveniles of S. carpocapsae are destined to become males and females, whereas H. bacteriophora develop into hermaphrodites that produce subsequent generations of males and females. Other differences include insect host range, population growth rates, specificity of bacterial phase variants, etc. This review attempts to compare EPNs, their bacterial counterparts and symbiotic relationships for further enhancement of mass producing EPNs in liquid media.

Lab-scale <i>in vitro</i> Mass Production of the Entomopathogenic Nematode <i>Heterorhabditis bacteriophora</i> Using Liquid Culture Fermentation Technology

“…However, in the case of Heterorhabditis bacteriophora, sexual mating is no concern because the first generation is hermaphroditic. Subsequent generations have amphimictic forms, which cannot easily mate in liquid culture [15,16]. As a result, mass production yield of Heterorhabditis spp.…”

Mass Production of the Beneficial Nematode Steinernema carpocapsae Using Solid State Fermentation

“…To many researchers, beneficial nematodes Heterorhabditis bacteriophora and Steinernema carpocapsae in vitro mass production on a large scale is challenging and cumbersome due to various obstacles [25]. The factors responsible for making nematode mass production difficult are: (a) phase shifting of the bacterial symbiont;…”

Biological Control Technology Utilizing Heterorhabditis bacteriophora and Steinernema carpocapsae

“…Biological control can affect pest biodiversity through predation, parasitism, pathogenicity, and competition (Ghosh, 2011). Entomopathogenic nematodes (EPNs), are highly virulent, kill their hosts quickly, are safe for the environment, humans, and other non-target vertebrates making them an attractive alternative to commercial pesticides (Mahmoud, 2016;Kooliyottil et al, 2013). Both Steinernema and Heterorhabditis nematodes possess three biological traits which render them useful as commercial pesticides: 1) a mutualistic relationship with highly virulent bacterium 2) a broad insect host range, and 3) their safety towards non-target organisms such as plants, livestock, and humans (Gerdes, 2015).…”