Insect Parasitic Nematodes Fact Sheet No. 5.573 Insect Series|Home and Garden by W.S. Cranshaw and R. Zimmerman*
Insect parasitic nematodes are small, nematodes. It includes a large number of Quick Facts round worms that complete part of their common but frequently overlooked soil- life cycle in insects. Several species can infesting nematodes that assist in organic • Insect parasitic nematodes kill insects in this process, and some are matter breakdown. are small round worms that marketed as a biological control agent. kill insects but are harmless to The use of insect parasitic nematodes other organisms. to control soil insects, including many Life Cycle • Several species of these turfgrass and garden pests, has received Insect parasitic nematodes are mobile increased attention recent years. Insect and move short distances in search of host nematodes are being parasitic nematodes are also know as insects. Heterorhabditis is more mobile than developed as biological insect predator nematodes, beneficial nematodes Steinernema. Nematodes use carbon dioxide controls. or entomogenous nematodes. They are and perhaps other chemicals produced in • Among the pests effectively sold under such trade names as BioSafe, waste products of insects as cues to find controlled are most turf BioVector, Scanmask, Exhibit, Oti-Nem, and their hosts. Upon entering the insect the insects and several other Guardian. nematodes kill their host by releasing bacteria Insect parasitic nematodes have been into it, strains of Xenorhabdus species that insects that live in soil. studied for potential biological control of are associated with the nematode. The turf pests for more than 50 years. However, bacteria develop within the body cavity of the their increasing availability and rising public susceptible host. The host dies from blood demand for alternatives to insecticides has poisoning within a few days. heightened interest in parasitic nematodes. The dead insect generally maintains Nematodes are a type of roundworm in its original shape and does not decay in a the phylum Nematoda. This is a different normal manner because its body is filled with order of animals from the segmented these specialized bacteria. Associated color worms, such as earthworms and flatworms. changes may occur. For example caterpillars Nematodes are abundant, particularly in parasitized by Heterorhabditis may have a soil. Many feed on bacteria, some attack reddish-brown color. The nematodes develop plants, and others can be parasites of animals. by feeding upon the bacteria and degraded However, each species is usually specific in host tissues. its habits. Insect parasitic nematodes, for The active stage of the nematode that example, develop only in insects or other invades an insect is the juvenile (dauerlarva) arthropods. They do not attack mammals, stage. These infective juveniles are applied for birds or plants. insect control. Steinernema nematodes enter Two genera of insect parasitic nematodes the insect through natural openings, such as have been most actively considered the mouth, spiracles and anus, then penetrate for control of insect pests. Steinernema into the body cavity. Heterorhabditis (previously known as Neoaplectana) has been nematodes use natural openings but also can thoroughly researched, including control enter by piercing the body wall. studies for Japanese beetle conducted in the Once inside the infected insect, 1930s. Recent attention has shifted to include nematodes develop rapidly, in five or the genus Heterorhabditis. Both groups are more days, depending on host quality in the order Rhabdita, the bacteria-feeding and temperature. Normally, one to two © Colorado State University generations occur in a host insect. Thousands Extension. 5/94. Revised 6/13. *W.S. Cranshaw, Colorado State University Extension of nematodes can be produced following a www.ext.colostate.edu entomologist and professor; bioagricultural sciences single infection. Ultimately, the body wall of and pest management; and R. Zimmerman, research the dead host insect ruptures and releases associate, Rogers Mesa Experiment Station, Hotchkiss. 6/2013 the nematodes. Insect parasitic nematodes typically kill their host insect within two to drying and ultraviolet light, three days after invading the body cavity. they are most effective against insects that occur in moist, dark locations. This includes various Safety and Environmental soil insects or borers within Concerns woody plants. Insects on foliage Insect parasitic nematodes do not may be susceptible in laboratory appear to have any significant harmful settings but control is poor in effects on other beneficial organisms or field applications. people. Arthropods appear to be the only Insect parasitic nematodes hosts for these organisms, so plants and are sold in the infective juvenile most wildlife are not likely to be directly dauerlarva stage, which are affected by nematode applications. barely visible to the unaided However, hosts can include some natural eye. They typically are used at enemies of insect pests, as well as the pest rates of 250 million to 2 billion species themselves. per acre (approximately 6,000 They cannot attack or cause disease to 46,000 per square foot). To in birds, mammals or fish. There appear apply, dilute the nematodes in to be minimal effects against noninsect water and drench the soil or arthropods, such as sowbugs and inject them into plants. Regular Figure 1: Life cycle of Steinernema nematodes. millipedes. Earthworms are occasionally spray equipment can be used – 1, 2: invasion and colonization of insect. 3,4: infected after wounding, but there is no nematodes are quite tolerant of pressures development within insect. 5: exit from dead evidence to suggest that insect parasitic found in many sprayers. insect and invasion of new host. Drawing courtesy of University of Illinois. nematodes harms earthworm populations in field applications. Steinernema Insect parasitic nematodes have Steinernema is the most widely Steinernema for control of white grubs. been exempted from federal and state researched species for insect control. It is Several species are sold including registration requirements (Vol. 47, Fed. the most readily available for yard and Heterorhabditis bacteriophora, H. megadis, Reg. 23928, 1982), greatly facilitating their garden use because it is easier to rear and and H. indica. development and distribution for insect handle. In field applications,Steinernema Heterorhabditis also effectively controls control. This means that insect parasitic carpocapsae tend to be most effective many nursery pests that feed in the root nematodes, like predatory and parasitic against caterpillar larvae. In laboratory and zone, such as black vine weevil and citrus- insects, can legally be used on all crops field trials, it has controlled sod webworms, infesting root weevils. without restriction. cutworms and certain borers (raspberry crown borer, carpenter worm). It also has Effects of Environment Insect Parasitic been effective against billbug larvae in Colorado State University trials. Other on Performance Nematodes for research indicates that adult billbugs may of Nematodes Insect Control be controlled as well. Effective use of nematodes for insect Insect parasitic nematodes are a Another species, Steinernema feltiae control depends on environmental biological insecticide similar to Bacillus is effective against certain fly larvae. It is conditions during and after application. thuringiensis-based insecticides. A wide sometimes used to control fungus gnats and Adequate moisture is the most important range of insects are susceptible to these other soil dwelling insects of greenhouse- factor. Insect parasitic nematodes require nematodes, at least in laboratory studies. grown plants. free water to move and are susceptible Various caterpillars and large beetle larvae Steinernema are less effective against to death by drying. High humidity and are among the more susceptible groups of white grubs, root maggots, rootworms and free water are the primary conditions for insects. Wax moth larvae, commonly sold black vine weevil. Unfortunately, some effective use of insect parasitic nematodes. as fish bait, are commonly used in rearing commercial products make claims of Insect parasitic nematodes also are insect parasitic nematodes. effective control of some pest species based susceptible to extreme temperature Maggots, crickets, grasshoppers and on research conducted solely in artificial conditions. For example, short exposure to termites appear less susceptible to the environments, these often do not reflect high temperatures (above 90 to 95 degrees commonly available strains of these performance in the field. F) can be lethal to commonly available nematodes. However other nematode strains of Steinernama carpocapsae. Low strains may hold future promise against Heterorhabditis temperatures (below about 55 degrees) these pests. Heterorhabditis is less commonly inactivate most Heterorhabditis species. One of the greatest factors to determine available because it is more difficult to rear Strain and species differ in temperature susceptibility under field conditions is the and more susceptible to environmental sensitivity. environment where the pest insect occurs. extremes. However, field trials consistently In soil applications, nematode Because the nematodes are susceptible to show that this genus outperforms movement to the target pest depends on even more damaging to insect parasitic Steinernema are effective against nematodes, and effects are persistent. caterpillar larvae, sod webworms, (Most of the pesticides that are seriously cutworms, certain borers, and billbug destructive to nematodes are no longer larvae. registered for use in turfgrass.) Heterorhabditis controls black vine weevil, citrus-infesting root weevils and Storage and Handling white grubs. Most insect parasitic nematodes Effective use of nematodes for insect packaged for sale have a shelf life of several control depends on environmental weeks or even months if refrigerated. Steinernema carpocapsae is particularly conditions during and after tolerant of storage conditions, a major application. reason for its ready availability. Systems to Most insect parasitic nematodes dry Steinernema nematodes for extended packaged for sale have a shelf life storage have been developed, a process that of several weeks or even months if can increase storage life and reduce the refrigerated. need for refrigeration. Regardless, insect parasitic nematodes can be killed or inactivated by extreme temperatures. Never allow them to freeze conditions of the soil and thatch. Adequate or be exposed to high temperatures (above moisture is essential and pretreatment about 90 degrees). irrigation is recommended. Irrigation may Information is still lacking regarding the also cause soil insects, such as white grubs, persistence of insect parasitic nematodes to move higher in the soil where they may in turfgrass under Colorado conditions. be more easily found by the nematodes. Native nematodes do occur in the state. Nematode movement is more extensive One of the most spectacular is Mermis in sandy soils with large pore size than nigrescens, often over 4 inches long, which in clay soils. Nematode penetration may is a common parasite of grasshoppers. For be expected to be poor in “tight” soils more information see fact sheet 5.610, common to some regions. Extensive thatch accumulation may also prevent nematode Weird Worms: Horsehair Worm and the penetration into the turf root zone where Grasshopper Nematode. white grubs feed. A post-treatment Commercially available strains have irrigation may help push nematodes originated from the southern United through the thatch layer. States or other mild climates. Those that Insect parasitic nematodes appear reproduce can produce multiple cycles compatible with many chemicals used of infection during the growing season. in lawn and garden care. Nitrogen However, it is likely that extremes of cold, fertilizers are nontoxic to Steinernema drying or high summer temperatures carpocapsae, as are insecticidal soaps would kill off nematodes under and wetting agents. Insecticides show Colorado conditions. variable effects on nematode survival, Furthermore, various soil organisms, with most having little effect. For example, including predatory mites, feed on the carbamate insecticides carbaryl nematodes and may reduce populations to (Sevin) and bendiocarb (Turcam) appear ineffective levels. In addition, there is some to be moderately toxic, particularly to dispersal of insect parasitic nematodes Heterorhabditis. Among tested turfgrass either through their own movements or by insecticides, chlorpyrifos (Dursban) is insects and mites. one of the most toxic to insect parasitic At present, there are no reliable nematodes. Mercurial fungicides are guidelines on nematode persistence.
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