Nematodes are tiny, thread-like worms that live all around us and even inside us. Although certain species are harmful, many are beneficial. Entomopathogenic nematodes are parasitic organisms that are certainly harmful to bugs but valuable for gardeners. In particular, Steinernema carpocapsae has several traits that make it an ideal agent for biological control of pests including armyworms, weevils, codling moth, corn earworm, cutworms, cabbage worms, leafminers and fruit flies.
S. carpocapsae is a fast and efficient killer. After a juvenile nematode infects an insect, the worm releases toxic bacteria along with venomous proteins. The insect dies in one to three days. After that, the nematode and bacteria reproduce within the cadaver; hundreds of thousands of nematodes can emerge from a single insect.
The next generations of nematodes (along with their symbiotic bacteria) will either affect new insects or rest in a dormant phase until more prey comes along.
According to ScienceDaily, one of the scientists, Adler Dillman describes the attack as “really science fiction-like…These microscopic nematodes crawl into the host, poop out toxic bacteria and then spit out the venom and turn the host into an insect milkshake."
In a strange twist, you can tell if a dead insect is providing shelter to a similar entomopathogenic nematode called Heterorhabditis bacteriophora because the cadaver will actually glow in the dark! The symbiotic bacteria associated with Heterorhabditis bacteriophora release a dim luminescence.
Steinernema carpocapsae is available commercially. Before investing in the nematode, be aware that is most effective at temperatures between 22C and 28C. Also, the nematodes affect a range of insects including beneficial ones that prey on pests.
Various species of entomopathogenic nematode can be found naturally in healthy soil. According to Penn State University, their numbers are highest in soils with minimal disturbance (particularly in no-till and minimum-tillage systems). They also thrive in soil covered with organic mulch. To nurture beneficial nematodes, take the same approach as you would to foster other soil life—keep the soil covered as much as possible (preferably with living plants), minimize tillage and cultivation, and avoid the use of pesticides and synthetic fertilizers.
Sources:
Using venomous proteins to make insect milkshakes. Sean Nealon, University of California - Riverside. ScienceDaily. April 20, 2017.
Activated entomopathogenic nematode infective juveniles release lethal venom proteins. Lu Dihong, Marissa Macchietto, Dennis Chang, Mirayana M. Barros, James Baldwin, Ali Mortazavi, Adler R. Dillman. PLOS Pathogens. Volume 13. Issue 4. 2017.
Insect-parasitic nematodes for the management of soil dwelling insects. College of Agricultural Sciences Cooperative Extension. Penn State University. 2005.
Biological Control: Nematodes (Rhabditida: Steinernematidae & Heterorhabditidae). David I. Shapiro-Ilan, GA Byron & Randy Gaugler. Cornell University. Online.
- Janet Wallace