Summary: Certain entomopathogenic nematodes (EPN) are efficient biological control agents that can be used against subterranean termites. That fact has been obscured by tests that emphasized soil-drench (inundative) treatment methods. Recent tests using EPN as inoculums in my nematode-optimized termite interceptors indicate that they reliably suppress even large, vigorous termite colonies.  Because EPN do not elicit complex avoidance reactions in termites exposed to them, repeated inoculations in EntomoBiotic™ Termite Interceptors should succeed, over time, in nullifying the ability of termite colonies to infest and damage manufactured structures and living botanicals such as trees and shrubs.  Furthermore, EPN should perform well as termite colony inoculants in all climates and environments suitable for termite propagation, without requiring the use of toxic chemical adjuncts. Scroll down to read full text of of article.  Next... Home...

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          Fig. 1. Subteranean Termite with an Entomopathogenic Nematode. The above drawing compares a subterranean termite worker adult (Reticulitermes spp.) of average size (5.5mm), with an infective juvenile entomopathogenic nematode (Steinernema spp.) of average size (850µm), both while stretched out in a straight line and as striking a pose typical for many Steinernematidae (the "S" shaped figure transposed on the posterior end of the termite's body).

Background

Nematodes are roundworms, or threadworms (the Greek word nema means thread) in the phylum Nematoda.  Some species live as parasites in insects and other organisms, often with no observable effect on the hosts, but in other cases causing effects ranging from minor discomfort to disease and death. 

Entomophilic nematodes have particular affinities for insect hosts.  Entomopathogenic nematodes (EPN) are entomophilic species that produce observable, deleterious effects on their insect hosts. In a paper published in the journal Biological Control, [Vol. 21, pp 230–248 (2001)], L. A. Lacey et al. note that as many as 30 families of nematodes are associated with insects. Scientists have focused on seven of these for their insect associations, and on other nematode families for their pathological associations with non-insect pests. 

An example of the latter is a nematode in the family Rhabditidae, Phasmarhabditis hermaphrodita, that infects slugs in the genus Deroceras. In a paper written for the Slosson Report (2000-2001), Harry K. Kaya reported that not only is P. hermaphrodita effective against a variety of slug and snail species, with control equivalent to chemical standards without adverse effects on non-target mollusks, but nematodes from two other families also show important molluscicidal activity against two slugs of economic importance, Deroceras reticulatum and Limax marginatus.

Many successful uses of EPNs to control insect pests have been demonstrated. Deladenus siricidicola, an EPN in the family Phaenopsitylenchidae, successfully controls the woodwasp Sirex noctilio. When inoculated along with a virus (Oryctes nonoccluded virus) and the fungus Entomophaga maimaiga, this same EPN successfully provides long-term suppression of the palm rhinoceros beetle Oryctes rhinoceros, and the gypsy moth Lymantria dispar. 

Romanomermis culicivorax Ross & Smith, an EPN in the family Mermithidae, successfully suppresses mosquito larvae and recycles at high levels in suitable habitats.  Only a low tolerance of conditions prevailing in certain host habitats, and the fact that Bacillus thuringiensis (subspecies Israelensis) provides equivalent control at less cost, keeps this EPN from being used extensively for mosquito control.

Of the six nematode families remaining, three have complicated life cycles that make mass production difficult.  These families, the Tetradonematidae, Allantonematidae, and Sphaerulariidae, are undergoing further study in a number of scientific laboratories and may prove useful in the future. 

Three other nematode families have demonstrated great economic success in insect control programs, due to a combination of host specificity and virulence, combined with ease of mass production.  EPN from two of these families cause host death soon after entering the insect's body (the Steinernematidae and Heterorhabditiae), while those from the third kills its host later, upon emerging from the host's body (the Mermithidae).

Unusually Viable EPN Families

Mermithid EPN parasitize invertebrate hosts in an apparently unremarkable fashion while completing certain portions of their life cycle. During this parasitic stage the EPN feeds on its host's fluids.  Though this weakens the host, it does not cause death; the insect is subjected--one must suppose--to considerable discomfort and annoyance by the presence of the nematode, but that is about the extent of the parasite's effect. When conditions are right, however, the nematode perforates the host's body and emerges, producing injuries that (especially in the case of insects) kill the host outright. These nematodes were first reported by Aldovandrus in 1623, after they were observed emerging from grasshoppers.

Steinernematids and Heterorhabditids, unlike the Mermithids, kill rather than parasitize insects (though some are capable of parasitizing, or forming symbiotic relationships with, other invertebrates in the absence of suitable insect hosts). Due to their phoretic relationship with a specialized bacterium, their insect hosts are killed, in general, within hours or days after they invade the host's bodies.  The amount of time between the EPN's invasion and death of the host varies according to environmental constraints such as, in particular, temperature.  At only a few degrees above freezing, for example, host morbidity and death may not ensue for weeks, while at room temperature the typical infection is lethal in 48 hours or less.

The effect of an attack by Steinernematids and Heterorhabditids on their insect hosts has been likened to that of a "guided missile" (Akhurst, R. J., 1993. "Bacterial symbionts of entomopathogenic nematodes", CSIRO Publications, East Melbourne). Immediately after entering the insect, the EPN disgorge their phoretic bacteria "warheads", which multiply and produce (1) a toxin that kills the host, and (2) antibiotics that preserve the host's cadaver.  The EPN feed on the bacteria and use the host's cadaver as an incubation chamber in which to produce multiple infective juveniles, or IJ's. Eventually the EPN IJ's emerge to search for new hosts.

Chance EPN Infections of Termites in Nature

Termites sometimes suffer chance infections from the Steinernematids or Heterorhabditids that become naturally dispersed in ordinary soil.  Though such infections often result in the death of the affected termite, the impact on the termite colony itself is generally minor and of limited duration, unless conditions are right for the EPN involved to mount repeated, massive intrusions into the termite colony's workings.

The disabilities that limit the natural virulence of EPN in the wild are well documented.  It is usual for those disabilities to be expressed in negative, rather than positive terms. In general, however, I believe we should be thankful that EPN are so disabled. Nematodes have an indirect influence on most aspects of our existence, yet they have so few direct, observable effects upon our lives that we are unaware of their ubiquitous presence. This paradox results from the fact that though these organisms are efficient propagators, they are also rather fragile. The following poetic description, though penned in 1914, remains undisputed today:

          “In short, if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes. The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites.”  Nathan A. Cobb

Natural Impediments to Virulence in EPN

Because EPN species are host specific, they can be trusted not to injure non-target organisms. Furthermore, though EPN succeed in infecting many of the insect hosts found in the soil they both inhabit naturally, they are unable to eradicate such hosts from that common habitat under ordinary conditions.  As occurs with parasites in general--including those with free-living propagules (structures like seeds, spores, and juvenile infectives, each capable of giving rise to  new, fully functioning organisms in kind)--nematode biology tends to rule against untoward virulence. 

In nature, EPN-insect interactions, though invariably lethal to the individual insects they manage to infect, are conducted in such a way that a kind of uneasy equilibrium is established. Thus, under ordinary conditions, EPN and their insect hosts coexist, though the hosts are somewhat fewer in number than would be the case absent the EPN. As a consequence, while a degree of insect suppression occurs, insect "control", to the extent that the insects are unable to carry out their characteristic patterns of behavior, does not.

By way of contrast, EPN-insect interactions that are bolstered artificially by man produce excellent control of many important insect populations. The subterranean termite is considered by many authorities to be a major exception to that rule. Termite and nematode 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. Not long ago, one imminent nematologist 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 article published on an early version of the Internet page Cornell University on biocontrol and nematodes. The language used in the present version of this web page differs somewhat, perhaps reflecting a positive change in the way academia views the use of EPN as agents for termite control.

Many other authorities in the fields of termite and nematode biology 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 have sought to isolate the various causes of nematode mortality.  Some focus on predators and pathogens, others on environmental factors such as temperature, moisture, pH, and the presence or absence of certain chemicals or nutriments. 

As you read the material that follows, remember the challenges implicit in Dr. Gaugler's remarks and in the negative reports published elsewhere. I asked, in response to the entire panoply of recognized obstacles, if it might be possible to interface EPN and termites in a setting that was free of all the cited issues. That question set the stage for subsequent investigations.

Pest Management with EPN

Most of the time, pest management objectives require that the targeted insect be (1) exterminated entirely or (2) reduced to population levels that leave them unable to cause economically deleterious damage. It is impossible to produce either level of insect control using EPN without instituting unnatural conditions that are orchestrated and maintained by man. Yet, by establishing an optimum set of such artificial conditions, a resourceful user can make EPN perform as effectively as chemical pesticides.  By fine tuning those conditions, a user can enable EPN to outperform many, if not most, chemical pesticide regimens.

Some user-established sets of artificial conditions work well with EPN against certain target insects. Others fail miserably against one target insect, but work well against others.  With target insects--like subterranean termites--that occupy unusual biological niches, ordinary EPN application techniques are ineffective. For example, in tests using singular, inundative applications of EPN to protect homes from large, vigorous colonies of subterranean termites, the EPN fared poorly.

Abortive Experiments with Inundative Termite Treatments

Under natural conditions, repetitious invasions of termite colony workings by large numbers of soil-based EPN almost never occur. However, it has long been theorized that--by using traditional inundative treatment methods--conditions could be produced with EPN that would protect homes from termite attack.  EPN are regularly applied inundatively as agricultural pesticides with great success, and exterminators and consumers have used chemicals and EPN in similar modes against termites since the 1940's. 

Inundative applications of pesticides can be made to cover an entire yard, or less expansively in narrow barrier inundations.  Professional termite managers often apply termiticidal chemicals using the latter approach. For years the inundative termiticide of choice was a mixture of the two chlorinated hydrocarbons chlordane and heptachlor. 

One inundation, or drench, of a band of soil around a home with a chlordane/heptachlor mixture can protect the home from termites for more than fifty years. After all uses for chlordane, heptachlor, and related chemicals were banned by the EPA in 1987, many less-persistent substitutes surfaced.  Today, an inundative termiticide is considered acceptable if its lethality, against termites, can be trusted to persist for five years or more.

Since certain EPN kill termites, it seems only logical to expect EPN to perform in inundative treatments, as do toxic chemical termiticides.  Inundating a band of soil with millions of EPN (e.g., one or more of the species Steinernema carpocapsae, S. feltiae, or Heterorhabditis bacteriophora) in an unbroken band around a wooden structure, would be expected to result in some degree of control over the termite colonies whose workings traverse the area.

In the 1980's and 1990's, Brad Kard, then a termite biologist with the U. S. Department of Agriculture (now professor of urban entomology at Oklahoma State University), tested soil-barriers using chemical termiticides in Mississippi while Roger Gold, professor of urban entomology at Texas A&M University, did the same in Texas.  A number of parallel tests were also undertaken using EPN.  Dr. Gold supervised many of the latter tests, and all of them failed. 

Not one of the documented experiments, performed anywhere in the world, using EPN in the mode of inundative termiticides, passed the test of persistence.  A five-year residual (the minimum standard for chemical termiticides) was out of the question.  Within months after EPN were placed in the soil around wood objects, termites breached the treated band and began feeding on the wood the EPN were "supposed" to protect.

On the surface, then, it seems contradictory that many homeowners appear to succeed in using EPN today, in inundative applications (both in whole yard and narrow band modes), to protect their homes from termites.  Statistics are not available to show how effective these treatments are. Anecdotal reports of successful experiences abound, however, despite the poor results of past scientific tests, and despite the existence of a long list of well-known EPN disabilities that scientists cite as the causes behind those dismal results.

Anecdotal evidence is unreliable, yet even rigorous scientific tests produce results that must be carefully interpreted. Scientific methods appropriate for one application may be inappropriate and/or inadequate for another. 

EPN and chemical termiticides work according to divergent, and largely incomparable, modes of action.  It follows, therefore, that testing regimens appropriate for one may be unsatisfactory for the other.  Scientific tests of chemical termiticide persistence, for example, use singular, rather than repetitive, termiticide applications. Chemical termiticides, following the lead of that historic benchmark, chlordane, are intended to produce effective, persistent barriers against termites with one soil drench event. Under similar conditions, however, inundative treatments with EPN will almost certainly produce negative results. Yet, under conditions better matched to EPN biology, a degree of acceptable control can usually be demonstrated.

Testing EPN on Termites in a Perfect World

Consider, for a moment, a hypothetically perfect world. How would EPN be tested against subterranean termites in such a place?

The answer, I believe, is that inundative methods would have been examined much as history records those tests today, and they would have failed. In a perfect world, however, scientists would never have accepted so anemic a defeat with finality. Instead, they would have performed additional testing engineered to take advantage of the known, innate faculties possessed by nematodes, while catching the targeted subterranean termites when and where they were most vulnerable. 

Examine for a moment the list of problems Dr. Gaugler pointed out. Can such as they justify the dismissive hand-wringing and intellectual indigestion we observe today? On the contrary, aren't they rather fodder for additional sleuthing? Nothing in that list suggests in the least that nematodes are unsuitable for termite control. The first thing Dr. Gaugler admits is how amazingly well nematodes do in the petri dish. Why on earth, then, would they not do well in the field? Serious investigators, who really wanted to give nematodes a chance, would not have allowed that question to rest unanswered.

The moment inundative methods with EPN produced less than stellar results, alternative methods for applying EPN should have been evaluated.  And, in a perfect world, such testing would have been scheduled and executed within a reasonable time period and with the same enthusiasm and coordinated effort as other tests conducted with chemical termiticides.

Alas, and alack. We don't live in a perfect world. Moreover--and let me be clear on this, as the foregoing may suggest to some that I think otherwise--it isn't the fault of our scientists. Ask yourself why the investigators at our universities should have been serious about giving nematodes a chance to perform as biological termiticides. They needed a real incentive, and there were none. Not only that, but their livelihoods were on the line, and they could not afford to take up a cause that nobody was the least bit interested in.

Scientific testing is costly, and not only in terms of equipment and facilities.  Though most scientists don't command salaries even remotely commensurate with the contributions they make to society, they and the institutions that employ them must be paid for their work. A perennial and urgent need for a continuous flow of new funding exists at most scientific institutions. This, in turn, forces such institutions to insist that their most senior scientists spend more time ferreting out new sources of funding than on performing, or coordinating, direct research activities. That's definitely not what most budding scientists look forward to, but it is reality--in the imperfect world we live in.

The lack I point out is rooted, not in academia per se, but in the market pressures endemic to capitalistic enterprise. But, lest the reader misunderstand, I (a confirmed capitalist in my own right) posit this opinion not as a negative, but merely as an indication of the current state of EPN research, particularly as it relates to the use of EPN for termite control.

Most funding for scientific research on particular kinds of termiticides comes from sources within the industries that produce those termiticides.  Please notice this:

Chemical producers are blessed with high margins that allow them to fund extensive, coordinated research projects that are geared toward promoting their proprietary molecules.

Nematode producers, by comparison, have no special rights over the propagation of the nematodes they produce, and are cursed with shoestring budgets that cannot be stretched to cover much, if any, out-of-house scientific research. This leaves a smattering of non-profit research foundations to pick up the slack for them. Non-profit research, for its part, is typically less coordinated and less intensive. Only rarely does non-profit research focus on promoting a particular method or agent.

Understandable, but Unwarranted Dismissal

Based on results derived from single-application inundative testing of EPN for termite control, most researchers within the fields of nematology, entomology, and the pest management industry rightly concluded that EPN could not be relied on as biological termiticides using that limited mode of treatment. The suitability of other modes of treatment remained unknown.  However, few of those alternatives were explored to any depth. 

The news that EPN failed to work in a limited field, i.e., as single-application inundative agents for termite control, was broadly extrapolated to the wholesale presumption that these organisms had no potential in the field of termite control whatever.  Today, on the basis of that presumption, many (if not most) termite biologists dismiss inquiries into potential uses of EPN with termites as a waste of time. Such dismissals, by competent scientists with impeccable credentials, abound in today's scientific literature, mostly in the form of terse and pithy comments accompanied by vague references to research showing one or more disabilities innate to nematode biology.

Such blanket dismissals are unsupportable.  Yet, few scientists have advanced serious challenges to them. Though scientific evidence exists to show EPN performing in other modes at levels similar to chemical termiticides, such evidence is scattered and obscure.  Together these facts act to bolster the unfavorable impression EPN have made on the field of termite control.  By comparison, a multitude of well-funded studies have produced long lists of chemical termiticides that remain effective in the soil up to fifteen years or more.

It is no surprise that the vast majority of consumers and applicators, today, choose from a wide array of chemical toxicants, and avoid the use of EPN, when performing termite prevention and control at homes and businesses.  Why risk failure with EPN, when success using chemical termiticides is almost guaranteed?

Safety is Worth the Risk

Why, indeed? Well, for one thing, because it is indisputable that EPN are safer, for applicators and consumers alike, than chemical termiticides. Newer classes of termiticides are so often touted as comparable in safety to bio-control agents that many, if not most, consumers and pest management professionals take that notion for granted.  However, a diligent search of the literature shows, conclusively, that even the safest of today's chemical-based termiticidal baits pose significant risks to those who are exposed to them. It is necessary to place those baits in child-and-pet-resistant containers for a reason, and no matter how hard man tries to do so, the leap from "child-resistant" to "child-proof" remains a dream (never mind the leap from "pet-resistant" to "pet-proof".)

EPN used for bio-control purposes, on the other hand, pose no danger to mammals, a fact that has been demonstrated time and again since 1935: 

         "Since the first use of the entomopathogenic nematode Steinernema glaseri against the white grub Popillia japonica in New Jersey (USA) (Glaser and Farrell, 1935), not even inferior damages or hazards caused by the use of EPN to the environment have been recorded*. The use of EPN is safe for the user. EPN and their associated bacteria cause no detrimental effect to mammals or plants (Poinar et al., 1982; Boemare et al., 1996; Bathon, 1996; Akhurst and Smith, 2002)." Dr. Ralf-Udo Ehlers Christian-Albrechts-Universität, Kiel, Germany, Safety and regulation of entomopathogenic nematodes.  [*Emphasis added].

EPN deserve serious attention, therefore, on the basis of safety alone. Today, our knowledge of EPN biology contains much of a positive nature with respect to their suitability as bio-control agents. In fact, every one of their well-known natural disabilities is, in reality, a positive attribute when viewed vis-à-vis the greater issue of mammalian safety. The truth is that EPN, when given a chance, are hardy organisms with amazing talents.  Many species appear well-adapted for controlling insects like termites. 

Contrary to accepted belief, EPN are able to persist in the soil for decades, if conditions are right. Still, the concept that EPN are weaklings, susceptible to every environmental condition imaginable, persists. One popular website confidently, but incorrectly, asserts that "(EPN) move no more than 18 inches in their lifetime on their own and will die in temperatures of over 70 degrees...". It may be possible to find EPN that can be described that way, but none of the EPN we have worked with are so handicapped. Many EPN are adept at hitching rides on or inside a variety of commensal or symbiotic hosts, and thereby travel long distances, and most survive when subjected to temperatures in the high 80's and low 90's. 

The range of environmental conditions suitable for EPN survival expands with each new spate of pure research, and with discoveries of new EPN species. That range grows even wider as investigators document the behavior of EPN as temporary parasites of earthworms and other, non-insect invertebrates. 

Giving EPN a Chance

I first began in-house evaluations of various termite-killing products in the early 1980's.  Later, in the 1990's, I began searching for novel termite control agents that could be used in termite bait stations I was developing. The possibility of a chemical-free, non-toxic solution, such as that offered by EPN, seemed particularly intriguing. 

Though initially with skepticism and reluctance, I  rolled up my sleeves and broadened the search for reliable, long-lasting ways to use EPN to kill termites. I did not know, then, if EPN could be made to work reliably and effectively for termite prevention or control, but I was convinced that they should be given a chance.  In particular, I believed that summarily denying them such a chance, based on the results of incomplete and inadequate testing methods, was unacceptable.

The Futility of Inundation Testing for Termite Control

One of the first facts I had to face was that soil inundation, regardless of the agent involved, is both the least precise, and the least economical, method of termite control imaginable. Inundating whole yards, or even narrow barriers, with massive amounts of residual insecticides is akin to laying a multitude of landmines to defend against a tiny number of small, scattered targets.  Such tactics are not only inefficient, but counterproductive. As with the typical landmine, while only a few desirable targets may be destroyed by activating them, nearby collateral (i.e., secondary, and in this context, entirely unintentional) targets are also destroyed, often with even greater efficiency. 

Though some termites are killed as they tunnel into the treated soil, the majority thrive without injury.  Tunneling workers that die on the job never make it back to the colony to entice their nest-mates to join them.

The effects of traditional, inundative treatments for termite control are intended, by the very nature of the treatment regimen, to be long-lasting.  The best agents to use with such treatments, therefore, emphasize chronicity over acuteness. Such methods have no utility with EPN (when used for termite control), which, by their very natures, emphasize acuteness over chronicity.  Little can be gained, therefore, by testing EPN against termites in this mode.  That such tests even took place illustrates the widespread lack of knowledge about EPN extant--then and now--within the field of termite biology. 

Historic Trends in Academic Research

As history is our guide, such a lack of knowledge is perfectly understandable. The state of termite biology in 1987 was dismal.  As long as chlordane reigned supreme, industrial sources of funding for research into alternative termiticides was scarce.  Since most academic research in termite control is industry funded, the direction industry takes tends to define the direction of university research.

Advances in academic knowledge took place at an astounding pace, once funding poured into termite biology projects.  A similar explosion in our knowledge about EPN-termite interactions is needed, yet few sources of funding are available.  Because it is difficult to patent EPN (it has been done, but the likelihood of patenting newly discovered EPN species with unusual features, and managing their distribution in order to control the market for them is poor), industry-based incentives to promote them are nonexistent. The number of studies carried out since 1987 on EPN-termite associations pales, in comparison with the mountain of studies conducted since 1993 on the effects of just one termiticide molecule, hexaflumuron. If you are reading this and you have deep pockets yearning to find a place to spend some of your discretionable funds, consider investing in entomopathogenic nematode research at one of the labs listed in the above link.  They can use the help.

Inoculation Challenges

Though no inundative termite treatment method (whether chemical or EPN) reliably eliminates termite colonies, inoculations with minute quantities of termite control agents are now known to utterly destroy termite colonies when used properly. As evidence of this fact accumulated, I wondered if basic termite detection and inoculation methods, using EPN instead of toxic chemicals, might neutralize or eliminate termite colonies as well. 

Ordinary bait stations are unsuitable for EPN inoculations, however. To give EPN a chance, conditions in the bait station have to be optimized, as much for EPN propagation as for termite attraction.  With an EPN-optimized bait station, the inoculated EPN and their phoretic bacteria might become what Dr. J. Kenneth Grace envisioned as the ideal microbial termite control.  As noted elsewhere, he wrote that such an ideal microbial agent would work as "a self-replicating time-bomb, akin to a computer virus" (J. Kenneth Grace, Sociobiology Vol. 41A, 2003, in an article entitled Approaches to Biological Control of Termites.)

Thus, instead of randomly distributed landmines with delayed fuses (e.g., using inundative techniques), the "time-bombs" Dr. Grace mentioned are planted in specific locations, in the precise number needed, and only inside specific kinds of desirable target organisms.  When the "time-bombs" go off, however, the result is not an explosion that damages unintended targets nearby, but is more akin to the opening of a gate, which frees the agents--from the case in which their clandestine development took place--so they can disperse and attack new target organisms with the same precision as their progenitors.

In actuality, EPN-infected termites behave like mobile, time-regulated misting devices. Outwardly quiescent, they lay dormant and innocuous until, without warning, the case (the termite cadaver) fractures and new EPN IJ's emerge. And because they are restricted to the workings of the termite colony, the IJ's have almost no opportunity to attack non-target organisms.  Confined within the termite colony superorganism, the EPN easily find new termites to infect, but little or nothing else.

Termites that become infected with EPN inside an EPN-optimized termite interceptor perform much like those coated with groomable toxicants.  They soon leave the interceptor and carry their potent termiticidal baggage deep into the termite colony's workings.  The process is similar to TTR, but without the laborious manual operations that accompany it.

To evaluate this idea thoroughly, I experimented with EPN applied in termite baits, inside an EPN-optimized bait station of our design.  In time a multitude of design features were discarded, improved, or revised.  It was discovered along the way that the bait station itself needn't provide, in situ, all the conditions needed for EPN to thrive.  It was enough to supply precursors to such conditions that EPN actuate at the time of inoculation. 

As field testing progressed, I better appreciated the importance of enlisting termites to do much of the necessary grunt work, again à la Tim Myles's TTR. 

Using Termite Ingenuity Against Them

Subterranean termites compensate for the often less-than-ideal environments in which their wood-based food sources are located.  If temperatures are too high or too low, they tunnel to more congenial places nearby and pipe that air over so they can keep on feeding.  Wood too dry gets a coat of mud, a splash of the termite worker's secretions, and as many drops of water--carried in from the nearest water source--as needed to bring up moisture levels.

Wherever they go, termite workers build and maintain a mud wall that encapsulates the colony on all sides, regulating its environment and eliminating undesirable fungi, bacteria, predators, and parasites. That's one reason why the subterranean termite colony, in combination with its system of workings, is often referred to as a superorganism.  The termite colony's workings--the mud walls of the tubes and enclosures that encapsulate the various sections of the colony--are crudely analogous to an animal's skin, a wrap that defines the extent of the colony's meanderings. 

Like skin, the workings of the termite colony protect vital interior constituents, while keeping out exterior contaminants. Subterranean termite workers, if forced to venture outside this skin, soon die from exposure.  Inside it, they live relatively long and healthy lives.  Some of the live termite specimens in my laboratory collections are over seven years old, and it is likely that a few of the termites that were alive when I first collected those specimens are still alive today.  Termite queens are capable of living twenty years and more.

The meticulous way termites regulate environmental conditions within their workings is similar to the way we regulate the interiors of our laboratories. Ironically, this hard work, which is necessary for their survival, can also be used by man to aid in their destruction. To do this one needs a device that (1) entices individual termites within a termite colony to congregate in one or more collection points to feed on cellulose bait, (2) provides the right environment for EPN infections to occur, and (3) facilitates repeated inoculations of EPN into the termite colony's superorganism.

These three basic criteria governed the design of my biologically-optimized termite bait station.  Following the terminology used by Ray Beal and Glenn Esenther, I eventually referred to it as a termite interceptor.

An EPN-Optimized Termite Interceptor

A termite interceptor optimized for EPN allows users to infect the termites inside it soon after they arrive.  It then continues to harbor residual EPN, which infect newly arriving termites as they enter the interceptor to feed.  This, along with periodic inoculations of fresh EPN into the interceptors by the user, maintains, simultaneously, a continuous and cyclic infection process.  Infected termite workers spread the EPN infection through the termite superorganism, inside a perfect enclosure, whose temperature-and-humidity-controlled environment is suitable for EPN and termites alike. 

Each infected termite becomes a ticking time-actuated release valve.  Generally, within one or two days or longer--depending on temperature and other conditions, the interval can be much longer-- the termite dies.  Because the cadaver doesn't putrefy, uninfected termites ignore it, with, perhaps, some (but not many) exceptions. Evidence of complex nematode avoidance responses by subterranean termites is sparse to nonexistent, especially with respect to the most common termite species, while evidence that termites ignore, or are attracted to and even cannibalize cadavers infected with EPN is abundant. Contrary to certain vague references found in the literature, we have observed no evidence that uninfected termites take steps to wall off EPN-infected members, alive or dead, from the rest of the superorganism (termites often wall off cadavers of nest mates infected with white or green muscardine disease, but the practice seems not to extend to cadavers infected with EPN). 

Generally, three to five days after being infected--temperature and other factors vary this interval considerably, up to and beyond twenty days--the termite cadaver bursts open, and tens or hundreds of EPN IJ's (along with larger adult male and female EPN) begin to emerge.  Afterward, additional IJ's continue to be produced within the ruptured termite cadaver, emerging in a slow procession for up to 20-40 more days.  As the IJ's that emerge from the termite cadaver attack, and invade the bodies of, termites that pass by, the infection cycle starts over, in a self-replicating cascade of re-infections within the superorganism.

As figure 1, at the head of this article, shows, the size of the EPN IJ is small, compared to the size of the average subterranean termite worker. The danger of immediate mechanical injury to the interior anatomy of the termite worker, by even multiple invasions of EPN, is low. Mature termite workers are not hindered from ordinary mobility by the commencement of an EPN infection. When immediate immobilization takes place, it is most common with immature workers whose diminutive viscera are more easily disrupted.  Mature workers, on the other hand, appear to continue ordinary activities in the immediate aftermath of EPN infections.  Once the IJ's mature into adult males and females, the onset of mechanical injury is inevitable, but for mature termites that does not occur for hours or days, during which time the termite worker is likely to travel, within the termite superorganism, a considerable distance from the infection site.

Close confines within the micro-workings of the termite superorganism are an artifact of the subterranean termite's innate thigmophilic nature.  The organism prefers to travel and live within a space that allows it to touch all sides of the tubular enclosure at once. Thus a termite worker constantly feels its way along its path, repeatedly palpating the floor, sides, and ceiling of that path.  This means that it will come into close, direct contact with whatever occupies its pathway as it passes by, and if that occupant is the cadaver of an EPN-infected termite, the emerging IJ's have a fighting chance of finding a new host thereby. 

EPN host-finding is improved if the termite worker loiters for one reason or another, and is improved again if the viscous fluids that seep from the cadaver, carrying a fresh load of EPN IJ's, contacts the live worker's body and sticks to it.  Even if the contaminated worker is not infected by the EPN in those fluids, it distributes them deeper into the colony's workings.  If the fluid sticks to the worker at a location near its mouth or anus--the favored ports of entry for Steinernematid EPN--the chance of infection is even better.

Not Quite Like Falling Off a Log

It is easier to describe how EPN can wipe out termite colonies than offer proof that they have done it.  Nan-yao Su occupied a spot similar to this in the late 1980's, as his experiments with hexaflumuron began to show success.  Dr. Su diligently collected and analyzed field data that eventually proved, to a level of certainty acceptable to most of his colleagues, that hexaflumuron eliminated termite colonies.  Our field trials, using EPN-optimized termite interceptors, are producing similar results.  As I learned from Su's experience, however, demonstrating termite colony nullification is a lengthy process, and only patience and diligence, in combination, deliver success.

As my field work continued, I constantly improved the design of the EntomoBiotic™ Termite Interceptor, Annunciator, & Inoculator (TIAI), and its method of use.  Where multitudes of technical challenges once loomed, most if not all have now been resolved.

My lab studies in Texas used procedures adapted from those described by Dr. Khuong Nguyen, a biological scientist at the University of Florida entomology and nematology lab.  Those studies, specifically designed to test various configurations of termite interceptors, showed that, although termites are uncommonly adept at resisting nematode infections under ordinary conditions, within the EntomoBiotic™ Termite Interceptor, Annunciator, & Inoculator (TIAI) it is possible to substantially increase the rate of EPN infection, to the point that termite colony nullification using EPN supplemented with other biological adjuvants is now a reality. 

More...

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Links to Articles, pro and con, on EPN/Termite Interactions:

Susan Jones, Ohio State University, discusses termite control with various termiticides, including nematodes: http://ohioline.osu.edu/hyg-fact/2000/2092.html  Dr. Jones refers to studies that suggest nematode avoidance by termites, including the walling off of dead or dying termite workers by uninfected termites. 

ARBICO, a supplier of entomopathogenic nematodes, discusses how to use them to control termites: http://www.biconet.com/arbico/biotermiticide.html

Parwinder Grewal, Ohio State Unviersity, discusses insect control with entomopathogenic nematodes: http://www2.oardc.ohio-state.edu/nematodes/  Dr. Grewal's website provides multiple links to other websites on the same subject.  Another of Dr. Grewal's papers is listed and linked to further down this page.

Brian Weeks et al, University of Arizona, discusses termite mortality from nematode infections: http://cals.arizona.edu/pubs/crops/az1359/az13591b.pdf

R. Weinzierl et al, University of Florida Extension Service, discusses various biological pest control methods, including those using nematodes: http://edis.ifas.ufl.edu/IN081  This article, along with others by the same authors, argues strongly against using nematodes for soil-barrier termite control, a view fully supported by our independent research.

G. C. Smart (Journal of Nematology, Vol. 27, No. 45, 1995) discusses entomopathogenic nematodes for insect control: http://nematode.unl.edu/_file33.pdf  This article kindled a great deal of interest in nematode research for insect control.

Parwinder Grewal et al, discusses entomopathogenic nematodes for insect control: http://www.scielo.br/pdf/ne/v30n2/a01v30n2.pdf  This article, published in 2001, goes into considerable detail on such topics as nematode biology, distribution, and mass production.

Please send suggested additions to the above list, or corrections to any of the captions provided, to jcates@austin.rr.com.

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