Why some insect-parasitic nematodes are called entomopathogenic nematodes? by Ganpati Jagdale

Entomopathogenic Nematodes- Nematode Information Insect-parasitic nematodes that belong to both Steinernematidae and Heterorhabditidae families are also called as entomopathogenic nematodes because they cause disease to their insect hosts with the help of mutualistically associated symbiotic bacterial pathogens.

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Kill Shore flies (Scatella stagnalis) with Entomopathogenic Nematodes by Ganpati Jagdale

  • The shore fly, Scatella stagnalis (Fallén) (Diptera: Ephydridae) is an important insect pest of greenhouse plants.
  • Larvae of these flies mainly feed on blue-green algae grown on the surface of plant growing media, walls, floors, benches, and pots.
  • But larvae can also cause a serious damage to tender plant tissues thus reducing quality and productivity of plants.
  • The adults are not considered as plant feeders but they are nuisance to people and disseminate pathogens such as Fusarium and Pythium from plant to plant as they disperse through the greenhouse.
  • Currently, most growers rely on chemicals that kill host plants such as blue-green algae to reduce the incidence of shore flies. However, this method has not been proved effective in reducing shore fly incidence.
  • Biological control agents including Bacillus thuringiensis var. thuringiensis (Bt) and entomopathogenic nematodes have been considered as alternatives to chemical pesticides.
  • For successful control of shore flies, entomopathogenic nematodes can be easily applied in water suspension as spray application to the surface of plant growing medium.
  • Entomopathogenice nematodes including Heterorhabditis megidis, Steinernema arenarium and Steinernema feltiae when applied at the rate of 50 nematodes/cm2 can cause 94- 100% mortality of shore flies.

How Entomopathogenic Nematodes kill Shore flies

  • When the infective juveniles are applied to the surface of plant growing substrate, they start searching for their hosts, in this case shore fly larvae.
  • Once a larva has been located, the nematode infective juveniles penetrate into the larval body cavity via natural openings such as mouth, anus and spiracles.
  • Infective juveniles of Heterorhabditis spp also enter through the intersegmental members of the larval cuticle.
  • Once in the body cavity, infective juveniles release symbiotic bacteria (Xenorhabdus spp. for Steinernematidae and Photorhabdus spp. for Heterorhabditidae) from their gut in the larval blood.
  • In the blood, multiplying nematode-bacterium complex causes septicemia and kills shore fly larvae usually within 48 h after infection.
  • Nematodes feed on multiplying bacteria, mature into adults, reproduce and then emerge as infective juveniles from the cadaver to seek new larvae in the potting medium/soil.

For more information on the interaction between entomopathogenic nematodes and leafminers, please read following research and extension publications.

  • Foote, B.A. 1977.  Utilization of blue-breen algae by larvae of shore flies. Environmental Entomology 6, 812-814.
  • Goldberg, N.P. and Stanghellini, M.E. 1990.  Ingestion-egestion and aerial transmission of Pythium aphanidermatum by shore flies (Ephydrinae: Scatella stagnalis). Phytopathology 80, 1244-1246.
  • Lindquist, R., Buxton, J. and Piatkowski, J. 1994.  Biological control of sciarid flies and shore flies in glasshouses. Brighton Crop Protection Conference, Pests and Diseases, BCPC Publications 3, 1067-1072.
  • Morton, A., Garcia del Pino, F., 2007.  Susceptibility of shore fly Scatella stagnalis to five entomopathogenic nematode strains in bioassays. Biocontrol 52: 533-545.
  • Morton, A. and Garcia del Pino, F. 2003. Potential of entomopathogenic nematodes for the control of shore flies (Scatella stagnalis). Growing Biocontrol Markets Challenge Research and Development. 9th European Meeting IOBC/WPRS Working Group "Insect Pathogens and Entomopathogenic Nematodes", Abstracts, 67.
  • Vanninen, I., Koskula, H. 2000. Biological control of the shore fly (Scatella tenuicosta) with steinernematid nematodes and Bacillus thuringiensis var. thuringiensis in peat and rockwool. Biocontrol Sci. Technol.. 13: 47-63.
  • Zack, R.S. and Foote, B.A. 1978.  Utilization of algal monoculture by larvae of Scatella stagnalis. Environmental Entomology 7, 509-511.