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 Beneficial Insects including Nematodes
Why Use Parasitic Nematodes? August 1, 2003
Entomopathogenic nematodes are very small worm-like organisms [actually parasitic roundworms] that live to kill other insects. The nematodes do not act alone; rather they serve as a delivery service for bacteria that kill the insect. A good way to think of this relationship is to picture a missile with an explosive warhead; the nematode is the "rocket and guidance system" which delivers the bacterium ("warhead").
How do they work?
The "infective juvenile" [usually the 3rd instar] stage locates a host insect, usually an immature form (larva or pupa) in or on the soil, enters the insect through the mouth, anus, or breathing tube. Once inside, the nematode releases the bacteria from its gut, and the bacteria starts growing, ultimately killing the insect. Meanwhile the nematode is feeding on both the multiplying bacteria and the insect. The nematode is also growing, developing into an adult, ultimately going through one or more generations (usually 2-3 life cycles per season) inside the carcass of the insect. As the bacteria and nematodes use the nutrients in the insect host, more infective juveniles (ijs) are produced which load up on the bacteria then emerge from the now long-dead insect and continue the cycle.
Two important entomopathogenic nematode genus are: Steinernema spp. the "ambushers" and the Heterorhabditis spp. the "hunters". If targeting vine weevils, root weevils, white grub or black weevils between late June and mid-September treat with Heterorhabditus spp. If you wanted to treat other pests earlier in the season as well as the above, a Steinernema and Heterorhabditus blend is the way to go.
A few organic farms on Vancouver Island are applying beneficial nematodes each spring as a preventative action. Some are cranberry growers, potatoes, vegetables and berry fruit growers. They are happy with the results, finding pest damage lessened to a degree where it is more acceptable.
There have also been cherry fruit fly and codling moth studies done in Yakima, WA by Dr. L. A. Lacey and others. Copies of these papers are available by request*. The research found that cherry fruit fly larva could be controlled to a certain degree with applications of Steinernema spp., between mid-June to mid-August as the larva drop from the tree.
Field trials for codling moth were done as a spray directly on the logs on in the bins where the diapausing (resting) larvae were located. They found on most trials the emergence was reduced from 31.2% to 83.4% and as high as 93.5% with one strain Heterorhabditus spp. High temperatures and low humidity have a negative impact on efficacy making the best season for control late February to late April. Temperatures would have to be about 12-15º Celsius for daytime application, although there is a new Steinernema strain that works well in cooler climates and is commercially available.
A short list of some pests controlled by nematodes;
Beans & Legumes - armyworm, cucumber beetle, cutworm, lesser cornstalk borer, white grubs
Berries - Banded fruit weevil, cranberry girdler, crown borers, cutworms, raspberry beetle, root weevils, strawberry moths, white grubs
Corn - Beet armyworm, black cutworm, corn rootworm, corn earworm, fall armyworm
Fruit Trees - European apple sawfly, codling moth, peach tree borer, stem borer, white grub
More about parasitic nematodes
*Donna Kimball
Technical Consultant
The Bug Factory
Email: mailto:donnak@thebugfactory.ca
Telephone: 250-468-7912 Fax: 250-468-9484
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