Page Intro: Heterorhabditis bacteriophora, Steinernema carpocapsae and S. feltiae are larval parasitic nematodes used for the control and management of various soil pests. On this page you will find a description, life-cycle info, benefits, drawbacks, scouting info, advisories, usages, and other good stuff such as ordering.
Description
These nearly-microscopic non-segmented roundworms called nematodes live in the soil and spend their lives exploiting the larvae and/or pupae of over 200 organisms for their own gain. They are entomogenous (en-toh-MAH-jen-us), meaning they develop on or within an insect. Aside from what’s listed here, there are other, less-common parasitic nematodes also commercially available: Heterorhabditis megidis, H. heliothidis (which is said to be synonymous with H. bacteriophora), Steinernema bibionis (a genus which is said to be synonymous with Neoplectana and species which is said to be synonymous with S. feltiae), S. riobravis and S. glaseri. These less-common nematodes will not be detailed here, though. Anyway, the three species discussed should be capable of solving all soil-pest problems which can be dealt with by using nematodes.
- H. bacteriophora (Hb)
- Hb are typically offered as live 3rd stage juveniles, (J-3) infective stage, commonly on sponges but sometimes on other media like vermiculite, are the product of choice when your problems concern lethargic, deeply planted pests: Japanese beetle larvae or grubs (Popillia japonica), for example. The reason: these nematodes boast a deep-moving (1-7"), active-hunting, “cruising” characteristic which make them superior to many other species for the purposes specified.
- S. carpocapsae (Sc)
- Sc are also typically offered as live 3rd stage juveniles, commonly on sponges but sometimes on other media like vermiculite, seem to be the product of choice when your problems concern more active, shallowly occurring pests: fungus gnat or mushroom fly larvae (i.e., Lycoriella, Sciara, Bradysia spp. and others), etc. The reason: these nematodes feature a shallowly-waiting-hunting (0-2"), “ambushing” characteristic which make them superior to many other species for the purposes specified.
- S. feltiae (Sf)
- Sf the largest of the nematodes mentioned, which are also typically offered as live 3rd stage juveniles as well, commonly on sponges but sometimes on other media like vermiculite, seem to be the product of choice when your problems concern, like that above, more active, shallowly occurring pests: fungus gnat or mushroom fly larvae, etc. The reason: these nematodes feature a shallowly-present habit (0-3"), like S. carpocapsae, but an intermediate active-hunting “cruising” characteristic, like H. bacteriophora, which may make them superior to many other species for the purposes specified. In fact, due to there shallow-cruising nature, S. feltiae are said to be the best nematodes for fungus gnat larvae. They tolerate cold better than the others as well.
A mixture of multiple species, such as Hb and Sc (which we offer) combined can be very useful in a single application against a variety or mix of pests or for certain pests which spend their lives doing different things at different depths depending on the time of day — black and variegated cutworms (Agrotis ipsilon and Peridroma sauci, respectively), which lie still by day and hunt on the surface at night, are a good example. An Hb/Sc mix is often used for fungus gnats in larger containers where the gnats are exploiting the container’s drainage holes. The Hb nematodes will work the deeper ground by the drainage holes, while the Sc nematodes guard the surface soils.
Other pests which can be controlled, or at least impacted, with one or more of the species discussed include: apple maggot pupae (Rhagoletis pomonella); black vine weevils (Otiorhynchus sulcatus); cabbage root maggots (Delia spp.); carrot rust flies (Psila rosae); carrot weevils (Listronotus oregonensis); spotted and striped cucumber beetles (Diabrotica undecimpuncata howardi and Acalymma vittatum, respectively); flea beetles (Podagrica uniforma); many fruit borer species (Synanthedon spp.); June/May beetles (Phyllophaga spp.); leafminer spp. pupae (i.e. Liriomyza.trifolii); northern corn root worms (Diabrotica longicornis); onion maggots (Delia antiqua); potato tuber worms (Phthorimaea operculella); squash vine borers (Melittia cucurbitae); strawberry root weevils (Otiorhynchus ovatus) wireworms (Limonius spp.); and many more economically important critters.
As mentioned, there are also other nematode species available to biocontrol practitioners. All boast a special, slight advantage over the others but, in actuality, for most practical purposes, the inexpensive Hb/Sc/Sf nematodes get the job done. However, there are some new strains being introduced which allegedly attack hosts which are unaffected by the nematodes mentioned. One example is Phasmarhabditis hermaphrodita; it attacks slugs but currently cannot be found in the United States — commmercially or otherwise. [Intro]
Life-style
The nematode species mentioned physically enter the host (grub, maggot, larva) and kill from within (endoparasitism). Entry is gained via the host’s mouth, anus or spiracles (breathing holes located along the sides of an insect). The Hb nematode, with its well structured and muscular, beak-containing head also has the ability to enter through the host’s soft, side-wall tissue. The Sc and Sf nematodes have more slender heads.
Before they can enter the host, though, it must be found. Both nematode species accomplish this by “tasting” or “sampling” the air [soil air] for the “flavors” of carbon dioxide, mainly, and also methane gas residues and warmth. The Sc nematodes will actually “stand” on the soil’s surface and waver back and forth — tasting, testing, sampling. If they lock onto a scent they will travel a short way to it, lie in wait for it or they might leap to it. In my company’s lab I’ve seen Sc nematodes actually leaping up to a centimeter in a petri dish containing moist peat and vermiculite. And that was cool!
In the case of the Hb and Sf nematodes, they simply search the soil, tracking down their host, slithering along the film of moisture surrounding the medium’s particulate matter, sampling as they go. Sf nematodes can and do stand on end like their Sc cousins, but do so in between movements and only “stand” a little.
Once inside the host, the nematodes settle in, shed a protective cuticle, mature, and begin feeding, defecating and reproducing. In their fecal matter lives a symbiotic bacterium enjoying the perfect harmony of interdependency with the nematodes. The bacterium present in the fecal matter of Hb nematodes is Photohabdus luminescens, in the Sc’s is the bacterium strain Xenorhabdus nematophilus, in the Sf’s the bacterium is X. bovienii. All types poison the host’s blood (called septicemia), thus killing it. The nematodes don’t actually do the killing, they just make it all possible and we all reap the benefits (except the old grub that is).
The life-span of these nematodes is roughly 8 weeks for Hb, 15 for Sc, and slightly more, up to 20 for Sf, all together — assuming the wax worm larva (Galleria mellonella — see Advirories) is the host used. The majority of the population progress through 4 immature stages J-1 thru 4. 1-3 they live in-vivo (inside their host), J-3 they’re ready to hit the road, J-4 and adulthood are spent in-vivo in their new host. Their life-cycle cannot progress beyond stage J-3 until they find a new host. This can artificially lengthen their lives, but for no good cause.
The conditions for optimum performance will be soil temperatures between 79-83°F for Hb with a low end of 65°F, 70-83°F for Sc with a low end of 60°F, and 70-79°F for Sf (which can handle the most cold) with a low end of 59°F. All prefer the soil, soilless medium, rockwool or other substrate, etc., to be moderately moist. But these are optimum conditions, and not necessarily a prerequisite of successful implementation. Please note, however, considerably cooler and warmer temperatures, as well as insufficient moisture levels, will hamper reproduction and development a certain degree.
Temperature can play an interesting role with nematodes, one that can be manipulated to a certain extent. For example: Hb’s bacterium requires a constant temperature of 60°F+ to break dormancy. However, Hb nematodes are active at 65°F. The same’s true for Sc nematodes: the bacterium needs 55°F+, and the nematodes are active at 60 degrees F. For Sf nematodes: the bacterium needs 54°F but the nematodes are active at 59°F. That means that soil temperatures must be monitored and nematodes used when conditions are not too cold, however soil temperatures above 90°F are too high, so they must be used somewhere in between, remembering that Hb nematodes can take the heat better while Sf nematodes deal with cold better. The nematodes can be put into the ground early, as long as no more freezes are expected; anytime indoors. (They will become active when the conditions are right.) In fact, the nematodes discussed here should be used whenever the target pest is in the ground in a susceptible form, usually larval, sometime pupal. Some releases should be made early in the season to catch spring pupating grubs, or later in the year when adults are laying soon-to-hatch eggs, but this all depends on which soil pest you’re dealing with. [Intro]
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