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Nematodes (the good)
Nematodes are simple roundworms. Colorless, unsegmented, and lacking appendages, nematodes may be free-living, predaceous, or parasitic.
Many of the parasitic species cause important diseases of plants, animals, and humans. Other species are beneficial in attacking insect pests, mostly sterilizing or otherwise debilitating their hosts.
A very few cause insect death but these species tend to be difficult (e.g., tetradomatids) or expensive (e.g. mermithids) to mass produce, have narrow host specificity against pests of minor economic importance, possess modest virulence (e.g., sphaeruliids) or are otherwise poorly suited to exploit for pest control purposes.
The only insect-parasitic nematodes possessing an optimal balance of biological control attributes are entomopathogenic or insecticidal nematodes in the genera Steinernema and Heterorhabditis.
These multi-cellular metazoans occupy a biocontrol middle ground between microbial pathogens and predators/parasitoids, and are invariably lumped with pathogens, presumably because of their symbiotic relationship with bacteria.
Entomopathogenic nematodes are extraordinarily lethal to many important soil insect pests, yet are safe for plants and animals. These are referred to as beneficial nematodes.
This high degree of safety means that unlike chemicals, or even Bacillus thuringiensis, nematode applications do not require masks or other safety equipment; and re-entry time, residues, groundwater contamination, chemical trespass, and pollinators are not issues.
Most chemical controls require days or weeks to kill, yet nematodes, working with their symbiotic bacteria, kill insects in 24-48 hr. Dozens of different insect pests are susceptible to infection, yet no adverse effects have been shown against nontargets in field studies.
Insecticidal nematodes are virtually without competition from other biological agents for control of soil-inhabiting and plant-boring insects.
Hundreds of researchers representing more than forty countries are working to develop nematodes as biological insecticides. Nematodes are sold in the U.S., Europe, Japan, and China for control of insect pests in high-value horticulture, agriculture, home and garden niche markets.
Insect sampling controllable by nematodes: