Beneficial nematodes are used in greenhouses to manage fungus gnats. Some growers have success using them to manage thrips also.
Are my beneficial nematodes alive?
After receiving a shipment of beneficial nematodes, it is important to access their quality before application. To do this, place a small sample of nematodes (5 ml) into a shallow container or Petri dish. Add one to two drops of tepid water, then wait a few minutes (about 10 minutes) and look for the actively moving nematodes. If the nematodes are alive, they will have a snake like movement or will be curled into a circle (“like a doughnut”). If they are dead, they will have a straight arrow-like appearance. You may see some dead nematodes, but most companies supply extra nematodes to compensate for the presences of any dead nematodes.
If using a microscope, it may be easier to see the nematodes if you have a light source from below, or if your light source is from above, placing the dish of nematodes against a black background as seen here.
Note: this photo was taken over one day after the nematodes were applied (it is recommended to apply the solution immediately), which accounts for the presence of the dead nematodes.
For more information see the fact sheet “Biological Control: Using Beneficial Nematodes”.