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 specially-designed nematode-optimized termite interceptors show 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 such devices should succeed, over time, in eliminating termite colonies entirely.  Furthermore, EPN should perform well as termite colony inoculants in all climates and environments suitable for termite propagation, without the need for exotic toxicant 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) 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).

Preface

Thus far in this series of articles the spotlight has cast its beam on such things as termite interceptors, termite interdiction, and termite colony inoculation. Often, within a single article, that light has cut a broad swath, so that it rested on two, or all three, at once. Here, and in the next seven pages, we shall constrict the beam somewhat, to illumine a much narrower subject, the biology of the entomopathogenic nematode (EPN). Our object will be the practical aspects of using EPN for termite control. In these pages we will wander into the heady world of scientific research, to discuss the methods used by universities and government agencies to evaluate the suitability of EPN for termite control.

I confess to feeling a certain dismay when confronting bias where none is supposed to exist. I get frustrated on encountering hastily formed, ironclad conclusions, arrived at on the basis of inconclusive evidence. If, by this, I betray a naiveté that might better have evaporated long ago, perhaps naiveté, in today's world, is underrated.

None who seek the truth can sit unmoved and silent when truth is neglected. Still, I recognize the distinction between productive and destructive expression. And that the prudent course is to speak one's truth with great care, after much reflection.

An eminent Oxford biologist, whose papers are unusually frank, wrote how frustrated he is with the proponents of a peculiar school of taxonomy, the transformed cladists. In a spirited style he relates how two of their number manage to "...debauch language and betray truth." Then he closes with the words "Now I'd better go out and dig the garden, or something." That is good therapy and great advice. I have done my share of digging the garden, both before and while writing--and re-writing--the pages that follow. I beg the reader's forgiveness if, as seems likely, I should have done more.

Introduction

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

Entomophilic nematodes have affinities for insect hosts.  Entomopathogenic nematodes (EPN) produce observable deleterious effects.  A paper published in the journal Biological Control, [Vol. 21, pp 230–248 (2001)], L. A. Lacey et al. notes 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. 

For example a nematode in the family Rhabditidae, Phasmarhabditis hermaphrodita, infects slugs in the genus Deroceras. In a paper written for the Slosson Report (2000-2001), Harry Kaya reported that P. hermaphrodita controls many slug and snail species with an efficiency equivalent to chemical control standards but without the adverse effects on non-target mollusks characteristic of chemical-based controls. Further, 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 Oryctes nonoccluded virus, and Entomophaga maimaiga, a fungus, 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, prevent 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. 

The three remaining 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).

Continued...

--Continue on to the next page in this article:

Page 2: Unusually Viable EPN Families

--Or to one of the other pages in this article:

Page 3: Natural Impediments to Virulence in EPN

Page 4: Pest Management with EPN

Page 5: Testing of EPN on Termites in a Perfect World

Page 6: Why Use EPN for Termite Control?

Page 7: Where Inundation Fails, Inoculation Succeeds

Page 8: Using Termite Ingenuity to Our Advantage

--Or proceed to the Next Article:  

Phoresy in Entomopathogenic Nematodes (EPN)

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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; however, our lab studies have failed to reproduce this behavior in any of the native subterranean termites we work with. 

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 jerry.cates@entomobiotics.com.

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