Just a quick tidbit of interesting info to share…
A recent reader question about predatory nematodes (and their usefulness in a worm bin) reminded me of the fact that I came across an interesting scientific journal article that discussed interactions between Eisenia fetida (our good friend the Red Worm) and Steinernema feltiae.
You may recall that I was quite pleased with the initial effectiveness of S. feltiae against a serious population of fungus gnats that had developed in my vermicomposting systems (see Steinernema feltiae – Fungus Gnat Killer). I also tested them against fruit flies (see Steinernema feltiae VS The Fruit Flies), but didn’t end up with any conclusive results unfortunately.
One of the things I wondered about in the case of adding the nematodes to a worm bin is the potential competition/predation from the bin inhabitants, including the Red Worms themselves. A composting system tends to have a much more diverse ecosystem than that found in regular soil or inert growing media – where these nematodes are usually applied. Undoubtedly the sheer numbers of the nematodes being added certainly helps to explain their initial effectiveness, but it seemed as though something was decreasing their overall potency over time (although, that being said, I should mention that I have not had a really bad infestation since then).
This article (see reference section below for more info) seems to support one of the hunches I had – that Red Worms do indeed kill off nematodes via passage through their digestive system. The researchers were actually wondering if earthworms could improve the effectiveness of the nematodes by helping to disperse them, but found that the opposite was true. The digestive enzymes of E. fetida are simply too potent to allow safe passage of the nematodes through their gut.
Definitely something to think about, especially if your vermicomposting systems have high worm densities (although, with high enough worm densities the threat of serious gnat/fruit fly invasions will be greatly reduced).
Campos-Herrera, R., Trigo, D., and C. Gutiérrez. 2006. Phoresy of the entomopathogenic nematode Steinernema feltiae by the earthworm Eisenia fetida. Journal of Invertebrate Pathology, 92: 52-54.