Chemical Free Termite Interdiction                                          

Termite Interceptors

Termite Control without Chemicals

Are Biological Agents Effective Alternatives?


Summary: We explored various biological agents as alternatives to chemical termiticides, evaluating each against seven different selection criteria.  Fungi such as Metarhizium anisopliae and Beauveria bassiana, and bacterial strains in the species Bacillus thuringiensis, appear unsuitable for use in termite interceptors because they evoke complex and efficient avoidance responses that lead termites to permanently abandon contaminated interceptors.  Baculoviruses in the genera Nucleopolyhedrovirus (NPV) and Granulovirus (GV) may have promise in the future, if virulence concerns can be resolved.  Entomopathogenic nematodes (EPN) in the families Steinernematidae and Heterorhabditidae have been found to evoke simple, but ineffective avoidance responses in isolated species of termites, but are ignored by most termite species during IJ incubation in termite cadavers, and (at least in the case of S. feltiae, the EPN most recently evaluated in our lab) tolerated by most termite species without evoking complex avoidance behavior upon IJ emergence..  However, as with other EPN we evaluated, S. feltiae can be relied upon to eliminate termite colonies only if repeatedly inoculated into nematode-optimized termite interceptors that resolve well-known impediments to EPN/termite interaction, such as those that have been described by Dr. Randy Gaugler, Rutgers University.  This limitation is considered a negative by some authorities, but is, in our view, entirely positive, in that it serves as an important indicator of termiticide safety. Were this limitation absent (and, thus, it became possible to eliminate termite colonies with single inoculations of EPN), we would consider their essential virulence an issue of significant concern. Scroll down to read full text of of article.  Next...   Home...


Live biological agents used for insect control include various species of fungi, bacteria, viruses, and nematodes.  All have proven effective as biological agents for the control of insect pests, and should be considered good candidates for biological control of termites.

All classes of biological control agents must be carefully, and fairly, evaluated as candidates for termite control.  Here we focus on those biological agents that are suitable for use in termite interceptors as termite colony inoculants.  To do this job right, a rational set of criteria is needed to select or eliminate each one. As more is learned, these criteria will change, and the list of acceptable biological agents may grow larger or diminish accordingly. 

Evaluation Criteria

The criteria used to select biological control agents to be inoculated into the EntomoBiotic Termite Interceptor, Annunciator, & Inoculator (TIAI) include all the items listed below:

1. The agent must be host specific to the point that it only produces mortality in arthropods.

2. The agent must be virulent enough to produce, under optimum conditions, 100% mortality within an intercepted termite colony.

3. The agent's virulence must be limited to the point that single inoculations are unable to destroy entire colonies.  This prudent criterion is necessary to exclude agents that pose untoward risks to the user and the environment. 

4. The agent must exhibit delayed morbidity and mortality. An agent that works too fast to debilitate or kill exposed insects lack the potential to distribute beyond the inoculation site.

5. Pathological effects caused by the agent must efficiently pass from infected individuals to other members of the termite colony.  Self-limiting diseases that succeed in killing only the individuals directly exposed to the inoculum lack the potential to distribute to the entire colony.

6. The agent must affect all termite castes, even if only certain castes (e.g. workers) are initially exposed to the inoculum directly.

7. The agent must not activate complex, instinctive avoidance responses in members of the termite colony.  Such responses lead to mechanical isolation of infected individuals and abandonment of contaminated food sources, thereby limiting the agent's potential to eliminate the termite colony.  An agent that activates simple, non-instinctive avoidance responses may be considered, as such responses are often ineffective at preventing infections.

Fungi: Beauveria bassiana & Metarhizium anisopliae

Several entomopathogenic fungal agents are well-known for their ability to cause insect disease and limit insect development within established ecosystems. Most propagate via asexual spores (conidia) that, by themselves, provide an excellent means whereby the fungi may be transported throughout a limited habitat, such as the workings of an active termite colony.  Various fungi have been thoroughly investigated as candidates for biological control of termites.  Two, Beauveria bassiana and Metarhizium anisopliae, produce unique variants of muscardine disease in the insects they infect.  Unfortunately, however, both also release repellants early in the infection cycle that alert uninfected termites to their presence.

Many termite workers may die before muscardine disease is curtailed within the workings of the termite colony. However, complex, instinctive behavioral responses by termites to fungal infections halt the infection's progress before the integrity of the termite colony is seriously threatened. 

During initial stages of muscardine disease, members of the termite colony become hyper-sensitive to evidence of the fungi's presence.  Strong avoidance instincts lead the termites to abandon contaminated tunnels and food sources.  This reactive behavior, which appears to follow the invasion of most virulent fungal pathogens studied to date, mitigates against the use of entomopathogenic fungi as repetitive inoculums in termite interceptors. 

Bacteria: Bacillus thuringiensis (Bt)

The most successful bacterial pathogen presently used in agricultural pest management is a gram-positive, rod-shaped, spore forming soil bacterium, Bacillus thuringiensis  (Bt). Over 800 varieties of this bacterium have been isolated, and all tend to be extremely host-specific.  Typically, as the bacilli are cultured for pesticide production, each bacillus produces a spore, and a crystalliferous protein composed oa spexcific endotoxin that leads to morbidity in the susceptible insects that ingest them. Some Bt strains also produce important exotoxins, along with chitinase and other insecticidal proteins capable of causing morbidity in susceptible insects on contact. In the main, however, ingestion of endotoxins and/or spores is generally required to produce a desired control.

The spore is the propagule for the bacillus. Although it will produce viable bacilli that reproduce in the insect's body, it usually does not proceed to the next step in the life cycle by producing fresh spores capable of extending the infection beyond the infected insect. Some culturing methods are designed to produce the right kind of endotoxins alone, absent the spores. Today, most over-the-counter Bt formulations sold for pesticide use are of the latter form.

The special endotoxin crystals produced during culturing generally comprise the most important active ingredient of Bt-based pesticides. The pesticide is applied to a substrate where the target insect is feeding, and the endotoxin crystals are ingested by immature stages of the target insect. Bt is very host-specific. The endotoxins produced by a particular strain, when introduced into the gut of a broad range of insect genre, will encounter conditions that allow it to produce morbidity in but a select few of them.  If the insect's gut chemistry is appropriate for the endotoxins involved, they will bond to and damage the gut membrane and cause it to become permeable to the endotoxins, the insect's native gut bacteria, and any Bt spores that may be present.  This leads to generalized septicemia and, within several days, death. The disease is generally self-limiting and does not spread beyond the insect that ingested it. Live bacilli are not present if only endotoxins are supplied (absent the spores), and in such cases the bacillus itself often does not participate in causing morbidity or mortality in the target insect.

Experiments with Bt against termite colonies have shown that inoculating Bt into active colony workings will kill most of the exposed termite workers.  The workers are affected only after ingesting cellulose contaminated with the endotoxins.  Soldiers and other castes within the colony are largely unaffected by the disease, as such caste members are fed via liquid food exchange, or trophallaxis, rather than by directly ingesting the endotoxin crystals. None of the forms of trophallaxis employed by termites appears to pass viable endotoxins or spores from a contaminated host termite to the beneficiary of its shared food

Prospects for achieving termite colony nullification using Bt alone are not promising. The cadavers of Bt-infected termites putrefy immediately after death, leading the uncontaminated workers to remove their bodies from the colony workings; if large numbers of dead workers accumulate at specific locations, their bodies may produce sufficient amounts of repellent products of putrefaction to cause their nestmates to abandon those workings and others nearby.  Avoidance responses to this pathogen, though possibly not as complex as those associated with entomopathogenic fungi, may eventually result in temporary abandonment of large, contaminated food sources. Residual quantities of Bt in such food sources may cease to be viable in the interim, so that they present little or no threat to the termites that eventually reoccupy the workings.

Even if Bt shows little promise as a stand-alone pesticide for termite control, various Bt strains may perform well in combination with other biological agents, especially when used as inoculums in specially-designed termite interceptors.  A synergistic effect may be achieved, for example, by inoculating termite interceptors with a mixture of Bt, entomopathogenic baculoviruses, and/or nematodes. Similar synergistic effects may occur with inoculations of Bt and organic, non-toxic, or least-toxic pesticides such as boric acid, borate salts (e.g., disodium octaborate tetrahydrate), potassium chloride, sodium citrate, etc.


Baculoviruses (NPV & GV)

Baculoviruses used in biological control of insects are mostly members of two subgroups, Nucleopolyhedrovirus (NPV) and Granulovirus (GV). Unlike most viruses, the typical baculovirus is visible under 400-1000X magnification using an ordinary light microscope.  The virus presents as a clear, irregular crystal, much like the appearance of tiny crystals of salt or quartz (NPV), or particles of sand (GV). 

Entomopathogenic viruses are host-specific, obligate parasites that cannot propagate outside of a host's body.  Inside the host, they take control of the genetic material within each cell to clone copies of themselves while destroying the integrity of the host's cell walls, thus liquifying the interior of the organism.  As infected organisms die, their bodies become so fragile that contact by other organisms causes them to rupture.  Fluids from the corpse's interior, containing huge quantities of cloned virus replicas, spill out and expose others to infection. 

The mode of action of the baculoviruses, in general, meets all the criteria we established for use in the EntomoBiotic Termite Interceptor, Annunciator, & Inoculator (TIAI) with one possible exception (limited virulence).  We are presently exploring this venue in greater depth.


Steinernematids and Heterorhabditids

Entomopathogenic nematodes are exempt from regulation by the Environmental Protection Agency. These organisms are known to kill insects, including termites, and have been used to fight agricultural pests for decades. As such, nematodes provide one of the most important methods of pest management on farms in America and throughout the world.  Their role in reducing the use of agricultural chemicals, and lowering exposures to hazardous pesticides for farm workers and consumers, cannot be overstated. 

Nematodes used in insect control produce mortality only in insects, though they are known to produce morbidity in certain other invertebrates. Though otherwise harmless to mammals, certain strains not used for insect control may, under extremely unusual conditions, produce morbidity in mammals as well.  The symbiotic bacteria associated with these nematodes, all of which are species in the genera Xenorhabdus and Photorhabdus, are not mammalian pathogens.  However, a nematode similar to those used in insect control (a close relative to Heterorhabditis indica that has not yet been assigned a species designation) has been isolated in Australia in association with a pathogen, Photorhabdus asymbiotica, var. Kingscliff, that has apparently caused an isolated number of cases of human morbidity there and in the United States. 

These developments do not alter the essential safety of EPN used as biological agents for pest management today.  They do illustrate an essential truth, however, that applies to all pest management processes:  a measure of caution is always wise, even when dealing with materials that are vouched for as safe by the most trusted of authorities.

Entomopathogenic nematodes are virulent enough to produce 100% mortality within an inoculated termite colony, yet their virulence is limited to the point that single inoculations are unable to produce colony nullification. Nullification of the termite colony, to the point where it is unable to infest and damage manufactured structures and botanicals such as living trees and shrubs, is only assured if repeated inoculations of the termite interceptors are carried out over a minimum period of twelve to twenty four months.

Delayed morbidity and mortality are important features of nematode infections. Once a termite is infected, it continues to travel within the termite colony's workings for hours to days afterward, potentially distributing nematodes far beyond the inoculation site. When the infected termite dies, its cadaver does not putrefy, and thus does not produce the chemical markers that trigger, in uninfected nest-mates, removal of the corpse from the colony's workings.  Instead, the cadaver remains inside the colony's operating superorganism, where it incubates a new batch of nematodes.  These emerge later to infect other members of the termite colony.

Though initial exposure to the inoculum in the termite interceptor involves mostly workers, all castes in the termite colony are susceptible to nematode infection.  As cadavers in the workings of the colony's superorganism release new batches of infectious juveniles (IJ's), any termites passing nearby--including reproductives and soldiers--become targets for new infections. 

Nematodes do not activate complicated, instinctive avoidance responses in members of the termite colony.  Studies have shown that many termite species, such as Heterotermes aureus, are unable to detect nematodes and take no evasive actions in their presence.  Other studies show that at least three termite species, Reticulitermes tibialis, R. speratus, and Coptotermes formosanus, detect the presence of nematodes in their colony's workings and take simple, though ineffective, evasive action as a result.  A study by Wu, et al., observed that, even though evasive action was taken by members of C. formosanus and R. speratus colonies, the response was so ineffective that nematode infections occurred anyway.  Even if the total number of infections were fewer with these species, repeated inoculations of nematodes into their colonies should, over time, result in eliminating the termite colonies involved.

Taking the Laboratory to the Real World

Important impediments, well-known to the scientific community, impose difficulties for EPN as agents of termite control. Although those difficulties are often cited as reasons why EPN are unsuitable for termite control, many of them actually make EPN more suitable in this role. A few of these difficulties, however, threaten to prevent EPN from performing at all unless they can be mitigated or resolved.  The EntomoBiotic Termite Interceptor, Annunciator, & Inoculator (TIAI) was specially designed to resolve these latter difficulties, and it did that by duplicating laboratory conditions in the field, so EPN could kill termites as well in  residential yards as they do in university research labs.

Admittedly, the barriers to so grand an achievement seemed to us, at first, insurmountable.  Termite biologists have fretted for years about the difficulties they've encountered trying to get EPN to work as well in the ground as they did in a Petri dish. One scientist explained it this way: 

          "In lab exposures, conducted in Petri plates, host-parasite contact is assured, host escape is impossible, and environmental conditions of temperature, moisture, and light are optimal for infection. In the field, behavioral and environmental barriers come into play and restrict host range. An experimental (i.e. lab-derived) host range should not be confused with field activity. Experimental host ranges can be huge. But in the real world there are barriers that can disrupt the infection process, frustrating control efforts and resulting in a far narrower spectrum of insecticidal activity." Dr. Randy Gaugler, Rutgers University, in an earlier version of a paper published by Cornell University on biocontrol and nematodes. The language used in the present version, published at the linked page, differs somewhat, reflecting an evolution in the way academia views the use of EPN as agents for termite control.

Note: Many other scientists have reached similar conclusions.  L. H. Ehler, in 1990, pointed out the superior reliability and consistency of chemicals, over nematodes, for insect control, spurring research into ways to improve their performance; Andrzej Bednarek, also in 1990, linked unpredictable nematode efficacy with poor persistence in the soil; J. Curran, in 1993, reported that 90% of the nematodes applied to soil died within a week; numerous investigations, by these scientists and others, have sought to isolate the various causes of nematode mortality, some focusing on predators and pathogens, others on environmental factors such as temperature, moisture, pH, and the presence or absence of certain chemicals or nutriments. 

In the above, it is worthy of note that Dr. Gaugler didn't assert that EPN cannot work in the field.  Instead, he listed impediments that, at the time, kept them from doing so.  What was needed, one gathers from his remarks, was a means of using EPN that was free of such obstacles, i.e., one that:

        (1) assures host-parasite contact,

        (2) makes host escape impossible,

        (3) insures that environmental conditions of temperature, moisture, and light are optimal for nematode infection of termites, and

        (4) resolves the behavioral and environmental barriers that restrict host range, disrupt the infection process, frustrate control efforts, and result in a narrow spectrum of insecticidal activity. 

To us, the challenge was clear. We asked if we could come up with a means of interfacing EPN and termites in a setting that was free of these obstacles, and the answer was yes, we could, given enough time, study, experimentation, and field testing. Of course, such a means would also have to be economically feasible.  The result took years of work replete with innumerable designs that failed. The first hurdles we had to get over involved selecting the best ways to attack the problem.

Inundation or Inoculation?

EPN are potentially able to kill termites as effectively as chemical termiticides.  Until the 1990's, the most common method used to control termites was to inundate a band of soil, around structures, with chemical termiticides. Soil inundation with nematodes, however, is not a reliable method of use for this organism, because that method does not enable nematodes to reliably overcome the obstacles Dr. Gaugler listed.

Another termite treatment method is inoculation. Timothy Myles, director of the Urban Entomology Program at the University of Toronto, developed several novel approaches to inoculating termite colonies with toxicants, beginning in the late 1980's. For example, Dr. Myles coated large numbers of individual termite workers with toxic agents, then released them back into the termite colony.  There they intermixed with their nest-mates, who instinctively groomed the coated termites, licking off the toxicant material and consuming part of it while passing the rest to other workers through a process known as trophallaxis. Dispersion of the coated workers through the termite colony, followed by diffusion of their toxicant coatings to their nest-mates, inoculated the entire colony with the toxicant material.

Dr. Myles refers to this highly effective inoculation method as Trap-Treat-Release (TTR). Though so labor intensive as to be impractical for many pest management professionals, TTR introduced inoculation to the pest management community as a progressive method of suppressing and eliminating termite colonies.  It demonstrated an important way to use instinctive termite behavior as an adjunct to other control schemes. It is fair to say we owe Dr. Myles a debt of gratitude of major proportions. Experimenting with the basic TTR concept taught us, and many others, important lessons in termite biology, field collection, and laboratory analysis of collected termite specimens.

Today, the most popular commercial method of inoculating termite colonies uses bait stations that feed toxicants to termites without requiring the practitioner to interface with the termites directly. Termite baiting was first seriously investigated by Ray Beal and Glen Esenther in the 1960's.  Interest in termite baiting remained low, however, until Barbara Thorne (presently professor of entomology, University of Maryland) and James Traniello (presently professor of biology, Boston University) developed a novel termite bait station in the late 1980's.

The device developed by Thorne and Traniello attracted termites to feeding nodes where they could be fed measured amounts of toxic baits.  The bait station they invented featured a removable bait cartridge that could be refilled with bait as it was being depleted by the termites.  Using such bait stations, they tested a fluorinated sulfonamide, sulfluramid, as a bait inoculum, with excellent results.  Based on their experiments, they pronounced the inoculated termite colonies effectively "suppressed" by the use of sulfluramid.  They did not, however, claim termite colony elimination, even though their studies suggested that some the termite colonies they treated had been annihilated in the process.  In those days, immediately following the chlordane ban, such claims would likely have been viewed with considerable distrust.

In the early 1990's, Nan-yao Su, a research entomologist at the University of Florida, used a similar bait station to inoculate termite colonies with the chitin-synthesis inhibitor hexaflumuron.  Dr. Su proved, with enough experimental data to convince even the most ardent skeptic, the utter destruction of large termite colonies using basic inoculation strategies.

Chemical or Biological Inoculants?

The genius of inoculation over inundation is that it needs only minimal quantities of a termiticidal agent to effect the desired control. However, the minimum quantity of agent needed varies as a function of its distribution and its mode of operation.  An agent that achieves rapid distribution, beyond the inoculation site, has greater potential than one that is stationary. On the other hand, an agent that produces putrefying cadavers has a limited potential for distributive poisoning, regardless of its other talents.

Sulfluramid, hexaflumuron, and a host of other chemical toxicants, appear to be excellent inoculums for termite control because they feature delayed morbidity and mortality, and are efficiently distributed and diffused by termites that ingest them.  However, the potential effects of any chemical pesticide on non-target organisms, such as humans and other mammals, should raise concerns in the minds of thinking persons.  It is sobering to observe a colleague afflicted by a chemically-induced disease, yet--and here I speak as a practitioner who has actively worked in this field for over twenty seven years and seen, in the process, sad things I never expected to see--examples of that are not uncommon within the pest management community.  Similarly--and, again, speaking from experience--learning after a long period of use that a chemical initially touted as being "as safe as table salt" has unexpected, serious toxic effects is another experience that pesticide applicators have had with surprising regularity over the past three decades.  It is wise, therefore, to be cautious, and not to trust in the safety of chemicals, especially if they belong to new, exotic classes, about which little is known.

Many authorities agree that whenever an efficacious non-chemical pesticide can be substituted for a chemical one, choosing the non-chemical substitute is generally the better course, especially if it is biologically based. The best minds in entomology consistently return to the biological arena to search for novel ways to make biological pesticides work better.  In the process, they often make exciting discoveries (e.g., TTR).  In between their exhilarating finds, they write of the problems they can and cannot overcome, and theorize about the features that ideal biological pesticides should have. It was apparently while so engaged that Dr. J. Kenneth Grace envisioned what he called the ideal microbial termite control agent.  It would function, he wrote, as "a self-replicating time-bomb, akin to a computer virus" See J. Kenneth Grace, Sociobiology Vol. 41A, 2003, in an article entitled Approaches to Biological Control of Termites.

Dr. Grace made his ideal termite control agent microbial, but it seems doubtful that he intended to exclude macrobials like EPN, many of which are (just barely) visible to the naked eye.  Consider the way such a macrobial termite control agent might behave:

          • At first, it hides inside its hosts so that other termites are not alerted to its presence. 

          • For some period of time afterward, the infected hosts unwittingly distribute the hidden agent by traveling from the inoculation site to other parts of the termite colony (as in TTR, per Dr. Myles, but with biologicals instead of chemical toxicants). 

          • After a pre-determined time, the agent kills its host.

          • Immediately, or some time later, it emerges to infect new termites. Again, this is similar to the way things work in TTR, where residual chemicals continue to intoxicate new termites who groom coated nest-mates, or who, via proctodeal feeding ingest toxicants defecated by others, or who become exposed to the toxicant by contacting the remains of dead termites; it differs from TTR, however, in that the agent reproduces inside the colony, resulting--over a period of days--in larger amounts of agent than the human user inoculated. 

Inoculation is at least one mode of treatment that potentiates what Dr. Grace described.  In order to work via this mode, however, the agent has to be non-repellant, with a delayed mortality that allows its distribution through the colony.  Either an epizootic (i.e., epidemic) or delayed mortality with such an agent would, in combination with non-repellency, have the potential to destroy the colony.

Though Dr. Grace mentions nematodes in his paper, he focuses on their failure as soil inundation agents, rather than on their potential as inoculants.  That focus is an outgrowth of the fact that an effective delivery mechanism for nematode inoculations of termite colonies did not exist at the time. Our research has taken the concerns voiced by Dr.'s Gaugler, Myles, Lewis, Grace and others, to heart, and led to the development of the EntomoBiotic Termite Interceptor, Annunciator, & Inoculator (TIAI).  By seeking to resolve the problems described by these distinguished authorities, we developed this device into an effective inoculation vehicle that is as effective as any of the chemical-based termite baits presently on the market. 



Links to Articles on Nematodes Used as Pesticides:

Randy Gaugler, Rutgers University, discusses entomopathogenic nematodes: This dynamic and evolving article includes considerable detail on the biology of various entomopathogenic nematode species.  Dr. Gaugler also discussed, in versions of the article published prior to February 2007, some of the difficulties scientists have encountered while attempting to maximize the effectiveness of these nematodes in the field.  As of February 2007 some of those details are no longer published, possibly in response to the advances we have made with the EntomoBioticâ„¢ Termite Interceptor..

Carmen Ugarte et al, University of Illinois, discusses the way bacteria-feeding nematodes in the soil serve to improve the availability of soil nitrogen:

University of Nebraska, Department of Nematology: Links to numerous papers and web-based articles on nematodes.

Diana Walls Laboratory, Colorado State University:  This links to a menu of QuickTime videos of various life stages of nematodes.  Videos shown were taken by Nicole DeCrappeo.

Aana Vainio, University of Helsinki, lectures on Entomopathogenic Nematodes:  Dr. Vainio discusses, in particular, European research and development in the field of nematology, using entompathogenic nematodes as biological control agents to reduce dependency on chemical pesticides.

Entomopathogenic Nematode Lab, Universidade dos Açores: This page discusses, briefly, the nematode research into, and the practical application of, entomopathogenic nematodes in the Azores.

J. Head et al, DEFRA, Sand Hutton, York, UK: Dr. Head discusses the use of the entomopathogenic nematode Steinernema feltiae to control the South American Leaf Miner. 

Elson Shields, Cornell University: Dr. Shields discusses the field persistence of the nematode Heterorhabditus bacteriophora, particularly the Oswego strain collected from northern New York State.

Richard Jansson et al, University of Florida: Dr. Jansson compares applications of an entomopathogenic nematode in aqueous suspensions versus infected cadavers for use as biological control agents.

Kirk Smith, biosys, Palo Alto, California: Dr. Smith discusses the control of weevils using entomopathogenic nematodes.

Please send suggested additions to the above list, or corrections to any of the captions provided, to