Method and composition for control of termite and shipworms

A composition and method for control of animal pests capable of nitrogen fixation is disclosed in which the active ingredient is a metal compound of either molybdenum or tungsten. It is disclosed that such metal salts of molybdenum and tungsten are uniquely toxic to termites and shipworms in low dosages. The composition can be incorporated into direct control agents, termite baits, soil inoculants, or may be incorporated with other ingredients in a wood treating dip or pressure treating composition for wood preservation.

TECHNICAL FIELD 
The present invention is in the field of methods and compositions for the 
control of animals capable of nitrogen fixation in general, and 
particularly for the control of termites and shipworms. 
BACKGROUND OF THE INVENTION 
While the present invention is broadly directed toward animals capable of 
nitrogen fixation, it is particularly useful in the control of termites. 
The prior art is generally cognizant of a wide variety of compounds which 
are useful either for introduction into wood for preserving the wood fiber 
from terminate infestation, of for directly controlling termites. Wood 
infestation and destruction by termites is a widely recognized problem, 
particularly in tropical and sub-tropical areas of the world and much 
research has been directed toward methods and compositions for controlling 
termite activity. Generally, in the prior art, it has been the practice to 
use either general organic insecticides or toxic metallic compounds to 
control or to kill termites. These compositions may be utilized directly 
to control termites by incorporated in a bait or attractant composition, 
but are typically utilized by injection or saturation in wood members so 
as to preserve wood which may come in contact with termite colonies. 
Exemplary of the prior art illustrating the use of general organic 
insecticides against termites is the disclosure of U.S. Pat. No. 
3,070,495, which describes the use of a decayed wood extract as a termite 
attractant so that the termites can be controlled by a conventional 
general organic insecticide, such as DDT, dieldrin, chlordane, parathion, 
malathion or others. Other examples are known in the art of packaging 
techniques for including such organic pesticides in baits, traps, or other 
devices intended to attract termites. 
The use of several metallic compounds have been proposed or disclosed for 
termite control. U.S. Pat. No. 2,784,139 discloses a composition for 
preserving wood including, as a mycocidal and insecticidal ingredient, one 
of a variety of metal compounds including chromated zinc chloride, copper 
sulphate, arsenic compounds, and mercury compounds. Similarly U.S. Pat. 
No. 2,886,486 discloses a wood impregnating compound including therein 
chromated zinc sulphate. More recently, the disclosure of U.S. Pat. No. 
3,832,463 illustrates the use of hexavalent chromium in a wood treating 
composition intended to preserve wood from microbial and insecticidal 
activity. It has also been proposed, in accordance with the disclosure of 
U.S. Pat. No. 3,993,752, to utilize an alkali metal cyanide added to a 
liquid fungicide including organic or inorganic sales of mercury, lead, 
tin, copper, or zinc to provide a wood treating composition having 
fungicidal and bactericidal properties. Further, it has been disclosed, in 
U.S. Pat. No. 4,132,780, that certain azide and metal salt formulations, 
including salts of iron, aluminum, nickel, maganese, colbalt, zinc, tin, 
or magnesium are capable of being used to control fungi and other 
micro-organisms. 
It has been proposed, in one known teaching in the prior art, to utilize 
molybdenum in a composition claimed to have biological activity. In the 
disclosure of U.S. Pat. No. 2,025,405, a method for producing a water 
soluble colloidal molybdenum compound contains valuable "pharmaceutical 
and bacteriological" properties. In addition, U.S. Pat. Nos. 3,290,343 and 
3,317,571 disclose certain compounds including molybdenum which are 
recited to be biologically active having use as pesticides. 
It has been known and understood for some time that a very small number of 
animals, including termites and shipworms, are capable of nitrogen 
fixation, in a fashion analogous to the nitrogen fixation of legumes. The 
animals themselves actually do not fix nitrogen. Instead, it has been 
discovered that among the microflora living in symbiotic relationship in 
the gut of termites are some capable of nitrogen fixation and they supply 
nitrogen in a fixed form to the host termite for protein synthesis. For 
example, Benemann in "Nitrogen Fixation in Termites", Science, Volume 181, 
page 164, July 13, 1973, discusses the phenomenon of nitrogen fixation in 
termites and suggests that the nitrogen-fixing agent is the intestinal 
bacterial flora of the termites. It is assumed that these symbiotic 
bacteria in the termite gut play an essential role in the nutrition of 
these insects since the wood used as food for the termite is very low in 
nitrogen. Another pest species that lives in and feeds n wood is the 
shipworm, a mollusk that is responsible for significant damage to wood in 
marine environments. The shipworm also supports large numbers of nitrogen 
fixing bacteria in its intestines, Carpenter et al., "Nitrogen Fixation in 
Shipworms", Science, Volume 187, pps. 551-552, 1975. 
It is known that among the nitrogen-fixing bacteria symbiotic with legumes, 
the enzyme nitrogenase, which is the enzyme responsible for nitrogen 
fixation, requires several atoms of molybdenum to be effective. It has 
been disclosed in literature that tungsten competes with molybdenum and 
may serve as an antagonist of molybdenum in the formation of this enzyme, 
Nagatani and Brill, "The Effect of Mo, W, and V on the Synthesis of 
Nitrogenase Components in Azotobacter vinelandii", Bioch. et Biophys. 
Acta, 362, 160-166 (1974). 
SUMMARY OF THE INVENTION 
The present invention is summarized in that a composition for control of 
nitrogen-fixing pests includes a pesticidal amount of an effectively 
soluble compound of a metal selected from the group consisting of 
molybdenum and tungsten. 
An object of the present invention is to also provide a method for the 
control of wood pests such as termites and shipworms and for the 
preservation of wood in which wood is treated with a composition including 
a pesticidal amount of a metal compound wherein the metal is selected from 
a group consisting of molybdenum and tungsten. 
It is an object of the present invention to provide a highly effective 
composition for termite and shipworm control which is economical to 
utilize and effective in its application. 
It is also an object of the present invention to provide such a control 
composition for termites and shipworms to which the organisms have no 
avoidance mechanism such that they will not actively avoid treated 
material. 
DETAILED DESCRIPTION OF THE INVENTION 
Broadly stated, the present inventon envisions a pest control agent for 
pests capable of nitrogen fixation which may be administered directly to 
the pests, or which may be used to protect wood from termite or shipworm 
infestation, and which includes, as its active ingredient, a compound 
preferably a salt, of either or both of molybdenum or tungsten. These 
metal salts of molybdenum and tungsten exhibit pesticidal activity in 
concentrations as low as 500 parts per million (ppm) of the metal 
ingredient. The concentrations of these metals may be reduced even lower 
if a more gradual rate of kill is acceptable and may, of course be 
increased to higher concentrations if it is economically feasible. The 
molybdenum or tungsten compounds conveniently may be introduced to the 
pests by treating the wood upon which pests would otherwise feed, or by 
inclusion into a pellet or other bait which is deposited in a location 
which the pests would frequent. It is envisioned, in particular, that 
salts of these metallic elements may be incorporated into wood treating 
dips or impregnating compounds which may be introduced under pressure into 
wood in a conventional treatment process to inhibit termite or shipworm 
feeding on that wood. 
The exact mechanism of molybdenum and tungsten toxicity on these organisms 
is not presently completely understood. The toxicity of tungsten was 
investigated under the thesis that tungsten would be an antagonist for the 
active metal cofactor of the enzyme nitrogenase, which is molybdenum. The 
enzyme nitrogenase is manufactured by the microflora in the gut of 
termites and shipworms. While the feeding of tungsten dosed cellulose to 
termites has proven toxic, it has been discovered unexpectedly in the 
course of the research on tungsten that small concentrations of molybdenum 
were equally, and, in some cases, even more toxic to termites than the 
dosages of tungsten. It is believed that either the termites, or more 
probably the microflora in their gut, include a biological "scavenging" 
mechanism specifically designed to isolate and absorb molybdenum from the 
environment. This same mechanism should exist in shipworms which feed on a 
similar diet. Since molybdenum is normally a relatively rare element in 
the diet of wood-eating organisms, providing these organisms with an 
excess supply of dietary molybdenum appears to cause the scavenging 
mechanism to introduce such a quantity of molybdenum into the animal's gut 
that the organisms die of molybdenum toxicity. It is believed that the 
tungsten toxicity to termites may be due either to the antagonistic 
activity of tungsten on the nitrogenase enzyme or to the molybdenum 
scavenging mechanism which might also accumulate tungsten. It is known, 
for example, that in some nitrogen fixing bacteria the mechanisms for 
molybdenum uptake also accumulate tungsten, "Molybdenum Accumulation and 
Storage in Klebsiella pneumoniae and Azobacter vinelandii, Pienkos and 
Brill, Jour. of Bact., 145: 2 pp. 743-751. It is to be understood, 
however, that the hypothesis for the mechanism of toxicity of molybdenum 
and tungsten is unproven at this stage. It is also possible that other 
mechanisms may be responsible for the molybdenum toxicity disclosed here. 
For instance, it is conceivable that the highly reducing characteristic of 
the microflora environment in the animal gut may cause metal salt 
precipitation in the gut which may interfere with other metabolic 
processes.

In order to give those skilled in the art a better understanding of this 
invention and appreciation of the advantages of the compounds formulated 
in accordance with the present invention, the following illustrative 
experimental examples are given: 
EXAMPLE 1 
The termicidal toxicity of various molybdenum and tungsten compounds were 
compared against various controls by testing of identical sets of 60 
termite larvae which were isolated in separate vials. All of the termite 
larvae were of the species Reticulitermes flavipes and were gathered from 
the wild in the around the area of Ingham County, Mich. Each of the groups 
of termites in the experiment were fed alpha-cellulose dosed with a 
solution containing the molybdenum, tungsten, or control salt dissolved in 
aqueous solution and formed into pellets. For low solubility compounds, a 
portion of the dosant was mixed as dry material in the pellets to complete 
the dosage amount. The pellets were, as indicated in the chart below, 
dosed with several test compounds. In each of the samples, the termites 
were observed over a period of thirty-two days or until the date at which 
50% of the termites were killed due to chemical toxicity. Results of these 
experiments and observations are summarized in the following Table I: 
TABLE I 
______________________________________ 
Concentration Published 
Dosant to the 
of Metal Days to Solubility 
Alpha-Cellulose 
p.p.m. wt/wt) 
50% Kill in grams/100 cc 
______________________________________ 
H.sub.2 O (control) 
-- &gt;32 -- 
CaSO.sub.4 (control) 
3,000 (Ca) &gt;32 .209 at 30.degree. C. 
no food (control) 
-- 22 -- 
CaCl.sub.2 (control) 
2,600 (Ca) &gt;32 -- 
MoO.sub.3 4,000 (Mo) 13 .049 at 28.degree. C. 
H.sub.2 MoO.sub.4 
5,000 (Mo) 13 .133 at 18.degree. C. 
CaMoO.sub.4 3,000 (Mo) 22 .0050 at 25.degree. C. 
Na.sub.2 MoO.sub.4 
5,000 (Mo) 13 39.38 at 28.degree. C. 
Na.sub.2 MoO.sub.4 
500 (Mo) 22 39.38 at 28.degree. C. 
Na.sub.2 MoO.sub.4 
50 (Mo) &gt;32 39.38 at 28.degree. C. 
FeMoO.sub.4 3,600 (Mo) 17 .0076 at 25.degree. C. 
Na.sub.2 WO.sub.4 
9,000 (W) 16 57.5 at 0.degree. C. 
Na.sub.2 WO.sub.4 
90 (W) &gt;32 57.5 at 0.degree. C. 
______________________________________ 
Materials providing 50% mortality to the termites within the experimental 
period are considered to be active against termites. In the experimental 
samples in which a 50% kill was achieved during the 32 day span of the 
experiment, most of the remaining termites typically died shortly 
thereafter. Note that higher level of the toxic additives caused termite 
mortality well before the termites which were starved (no food control) 
died. 
The symptoms of the molybdenum toxicity to the termites included that the 
abdomens of the termites turned blue-grey after a relatively short period, 
i.e. three days, of feeding on the dosed cellulose samples. No such 
phenomenon was observed with control termites or termites feeding on 
tungsten dosed pellets. 
Also in the above experiment, in the sample of termites which were fed 
sodium molybdate at a concentration of 5000 p.p.m., the termites were also 
allowed access to pellets inoculated only with distilled water. The 
termites in this sample exhibited no avoidance of the molybdenum dosed 
pellets thus suggesting that termites would not be capable of avoiding 
molybdenum treated wood or cellulosic baits containing molybdenum or 
tungsten in their environment. 
EXAMPLE II 
To verify that the observed toxicity is attributable to molybdenum, and not 
simply to the presence of a metal salt, an additional test was run with a 
variety of metal salts. Two samples each of fifty individual 
Reticulitermes flavipes worker larvae were fed kraft paper pellets dosed 
with metal salts. The metal salt compounds were dosed onto the pellets by 
being dissolved in water and deposited on the paper. The temperature and 
environmental conditions were constant and the pellets were periodically 
moistened with water. Results of these tests for each of the following 
metal salts are summarized in Table II below: 
TABLE II 
______________________________________ 
Percent 
Survival 
Dosage (mg per 
Days to at 48 
Dosant 5 gram paper) 
50% Kill days 
______________________________________ 
NaNbO.sub.3 9.03 -- 95 
NaBiO.sub.3 14.80 -- 88 
None (Control) 
-- -- 91 
NaVO.sub.3 6.50 -- 58 
Na.sub.2 B.sub.4 O.sub.7.10H.sub.2 O 
19.80 8-10 0 
CuCl.sub.2 .2H.sub.2 O 
9.38 -- 81 
Na.sub.2 MoO.sub.4.2H.sub.2 O 
12.5 24-28 1 
Na.sub.2 SnO.sub.3.3H.sub.2 O 
13.9 -- 89 
CoCl.sub.2.6H.sub.2 O 
12.4 -- 83 
Na.sub.2 WO.sub.4.2H.sub.2 O 
17.30 37-49 19 
NaCl 9.18 -- 91 
Fe.sub.2 (SO.sub.4).sub.3.3H.sub.2 O 
12.20 -- 93 
SrCl.sub.2.6H.sub.2 O 
13.90 -- 88 
FeCl.sub.3.6H.sub.2 O 
14.30 -- 90 
MnCl.sub.2.4H.sub.2 O 
10.30 -- 92 
NiSO.sub.4.6H.sub.2 O 
13.90 -- 62 
TiO.sub.4 4.37 -- 81 
NH.sub.4 Al(SO.sub.4).sub.2.12H.sub.2 O 
23.60 -- 92 
MgSO.sub.4.7H.sub.2 O 
12.50 -- 90 
BaCl.sub.2.2H.sub.2 O 
12.50 -- 87 
NaI 7.83 17-24 18 
Ce(SO.sub.4).sub.2.4H.sub.2 O 
21.50 -- 92 
NaTaO.sub.3 4.37 -- 88 
LiCl 2.20 -- 86 
ZnSO.sub.4 .7H.sub.2 O 
15.00 -- 86 
______________________________________ 
The amount of metal salt in each of the above samples was formulated to 
give an effective concentration of 1000 p.p.m. of metal in the termite 
food, with the exception of NaCl (dose tripled) and Fe.sub.2 
(SO.sub.4).sub.3 (dose cut by one-half). The kill rate of the boron 
compound was expected inasmuch as borate is a previously documented 
termiticidal (and general insecticidal) agent. However, borate is very 
soluble and not amenable to easy methods for making insoluble, and thus 
its effectiveness in wood treatment is very limited. The use of molybdenum 
does not suffer from such a limitation. 
EXAMPLE III 
To verify that a wide variety of molybdenum compounds are effective, 
another test was run using a variety of molybdenum and one tungsten 
compounds. The method of dosing the compounds onto the termite feed, again 
kraft paper pellets, varied according to the solubility of the compound. 
The more soluble compounds were introduced entirely in aqueous solution, 
while for some of the less soluble compounds part of the dosage included 
dry material added to the pellets. The molybdenum disulfide, which is 
absolutely insoluble in water, and the molybdenum were ground and added to 
the pellets only in granular form. The amount of metal compound in the 
paper pellets was selected to give a concentration of 500 p.p.m. of metal 
in the sample, escept for the MoS.sub.2, which was at a dosage of 5000 
p.p.m. A single sample of 60 termites was used for each sample, and the 
results are summarized in Table III below: 
TABLE III 
______________________________________ 
Published 
Number dead (of 60) 
Solubility in 
Dosant at end of Four weeks 
grams per 100 cc 
______________________________________ 
H.sub.2 O (control) 
3 -- 
Na.sub.2 MoO.sub.4 
20 39.38 (at 28.degree. C.) 
(NH.sub.4).sub.2 Mo.sub.2 O.sub.7 
13 43 (at 25.degree. C.) 
H.sub.2 MoO.sub.4 
16 .133 (at 18.degree. C.) 
MoO.sub.3 11 .049 (at 28.degree. C.) 
Mo ore 18 -- 
MoS.sub.2 0 0 (effectively insoluble) 
NaWO.sub.4 
26 57.5 (at 0.degree. C.) 
FeSO.sub.4 
0 -- 
Na.sub.2 Cr.sub.2 O.sub.7 
0 238 (at 0.degree. C.) 
______________________________________ 
Again in this test the metal salts were dissolved in water and deposited on 
the paper in solution. The molybdenum ore, which was raw ore obtained from 
Climax Molybdenum Co., was unrefined ore from a sample designated 77-2A by 
Climax. The assay of the ore was represented to be 0.263% Mo and 2.15% 
FeS.sub.2. 
This test showed that a variety of very soluble and marginally soluble 
molybdenum compounds are effective termicidal agents, while the virtually 
insoluble molybdenum disulfide apparently is not, at least under these 
conditions. 
Very few animals are capable of fixing any appreciable amounts of nitrogen 
gas from the atmosphere, other than termites and shipworms. To verifty 
that this pesticidal effect related to nitrogen-fixation ability, samples 
of molybdenum and tungsten compounds were fed, in dosages lethal to 
termites, to other pests such as fire ants, cockroaches and bark beetles. 
These pest insects were not killed by these compounds thus demonstrating 
that they are not broadly toxic to insect species. It is also known that 
molybdenum and tungsten compounds are relatively non-toxic to plants and 
to other animals, in contrast to many currently used termicidal agents 
which are broadly toxic to many organisms. 
Thus, it can be readily appreciated that metallic salts and other 
effectively soluble compounds of molybdenum and tungsten exhibit 
significant and unusual toxicity to termites through some mechanism 
related to the ability to fix nitrogen. While it is believed that the 
mechanism of this toxicity is related to the mechanism for molybdenum 
uptake to create nitrogenase enzyme for the fixation of nitrogen, as 
stated, it is also possible that the toxicity mechanism results because of 
the strong reducing activity of the microflora gut. It is to be 
understood, therefore, that the present invention is not limited to the 
mechanism for this toxicity which is discussed here, but is instead 
directed toward both a composition for the control of nitrogen fixing 
pests including molybdenum or tungsten and a method for using these 
compositions to control pests regardless of the details of the mechanism 
by which they function. 
It is envisioned that this termite control composition can be utilized in 
any conventional wood treating composition already containing fungicidal 
or other preservative compounds. The inclusion of a small amount of a 
molybdenum or tungsten metallic salt or derivative would also ensure that 
the treated wood would be safe from termite and shipworm infestation. 
Alternatively, these metallic salts for pest control could be incorporated 
in cellulosic pellets or baits which could be placed in pre-selected 
locations adjacent to the wood likely to be visited by the pests. A 
quantity of cellulosic material, such as wood, paper, paperboard, paper or 
paperboard products, or cotton, needs merely to be inoculated with a dose 
of a molybdenum or tungsten compound, and left as a bait in a location 
likely to be frequented by the pests. Alternatively, to protect wood 
structures such as housing, etc., molybdenum or tungsten compounds could 
be directly inoculated in the soil surrounding the structures. By use of 
such a bait, termites could be controlled in a structure regardless of 
whether or not the remaining wood in a structure to be protected was 
susceptible to treatment. 
It is to be understood that a preferred method for using the compositions 
of the present invention is to impregnate the compositions directly into 
the wood to be protected. Such impregnated wood would be resistant to both 
termite and shipworm infestation. To be effective as a wood impregnant, 
the molybdenum compound must be in a form that prevents it from being 
immediately solubilized when the wood is exposed to water. One method 
would be to soak the wood in a highly soluble molybdenum (i.e. molybdate) 
solution under heat or pressure to introduce the compound into the wood. 
Wood with insoluble molybdenum impregnated therein would be particularly 
useful in marine applications where shipworms are a problem. 
An alternative approach to introduce an relatively insoluble molybdenum 
compound into wood is to use a suspension of an insoluble compound as very 
fine particles which can be forced into wood pores under pressure. Another 
approach would be to use an organic solvent to dissolve a relatively water 
insoluble molybdenum compound to carry the compound into the wood. 
It should be appreciated that a wide variety of concentrations of many 
molybdenum or tungsten compounds is possible within the spirit of the 
present invention as long as verifiable toxicity to termites and shipworms 
can be achieved. It is believed that the reasonable interpretation of the 
test data presented here is that any molybdenum or tungsten compound which 
is either effectively soluble in water or which otherwise makes its metal 
constituent biologically available to a pest when digested will be 
effective. By effectively soluble as used herein it is intended to mean 
compounds having some measurable solubility. By biologically available it 
is intended to mean compounds wherein the molybdenum or tungsten molecules 
are available for uptake by the host animals. From these parameters, it 
should be clear that a wide variety of salts and other compounds of each 
of these metals can be efficacious. It is also envisioned that such 
compositions in accordance with the present invention could be effectively 
used as soil inoculants in or around structures to be protected to prevent 
termite encroachment upon the structures through subterranean tunnelling. 
It is understood that the present invention is not limited to the 
particular embodiments disclosed and illustrated herein, but embraces all 
such modified forms thereof as come within the scope of the following 
claims.