HK1111061A - Pesticide compositions and methods - Google Patents

Description

Pesticide compositions and methods

The present invention relates to novel pesticide compositions comprising alkyl formates and isothiocyanates, methods of delivering fumigants and methods of controlling pests using combinations of fumigants.

Background

Fumigants are widely used for killing insects and protecting against infestation by pests, and are often required for protecting particulate products (e.g. cereals) and other stored products (including durable and perishable food or cut flowers), porous bulk materials (e.g. soil or wood) and spaces (spaces) (empty buildings or those containing produce). Ideal fumigants should be toxic to insects, rodents, mites, nematodes, bacteria, fungi and their spores, viruses and moulds and other pest biota. It should be effective at low concentrations. Ideally, it should be low absorbed by the material in the fumigation zone. It should have low phytotoxicity to the product. It should have low chronic mammalian toxicity and no or inert residues. Furthermore, the ideal fumigant should provide safe handling without difficulty, and it should not adversely affect the product or space being fumigated.

None of the fumigants meet all of these "ideal" criteria. The two fumigants most commonly used for fumigating grains, other particulate materials, fruits and wood are phosphine and methyl bromide. However, the use of methyl bromide is expected to be phased out in australia and other developed countries after 2005. Recently, carbon disulphide has been proposed as an alternative to these fumigants (WO 93/13659), but it is not re-registered as a fumigant in New South Wales, australia. Thus, it is expected that phosphine will become the only registered fumigant available for agricultural use in australia.

Phosphine is a preferred fumigant for stored grain and the like because it is effective against grain pests and leaves little residue (essentially harmless phosphorus compounds). However, phosphine is pyrophoric when its concentration exceeds a relatively low value, and when used at acceptable concentrations, does not kill all stages of insects in a short period of time.

Fumigation with phosphine requires prolonged (> 5 days) contact at temperatures above 15 ℃ in a closed grain box. Many existing agricultural tanks are not sealed and therefore not suitable for effective fumigation because the concentration cannot be maintained for the time required to control all pests. The excessive dependence on phosphine in australia and the unsealed bin has led to: (1) higher frequency of resistance, (2) hazardous practices and (3) the grain is transported to a barn containing live insects and unreacted aluminum phosphate residue.

Alkyl formates such as ethyl formate and methyl formate have a long history of use as fumigants for stored products. Ethyl formate is currently registered in australia as a dry fruit fumigant and is now being investigated as an alternative fumigant for cereals stored in unsealed agricultural containers. Care must be taken to keep the concentration within the structure below flammable levels when alkyl formates are used. This is achieved by controlling the rate of vaporization of the alkyl formate by avoiding accumulation of liquid alkyl formate at the bottom of the structure in which the grain is stored, while maintaining an effective concentration within the structure for a sufficient period of time.

Cyanogenic compounds such as hydrogen cyanide and cyanogen chloride, chlorine and arsenic-containing gases have been used with more or less success as fumigants, disinfectants and for repelling insects and animals, respectively, over time.

Known as cyanogen gas (C)₂N₂) Is a highly toxic drug and has recently been found to be suitable as a fumigant (WO 96/01051). Dichlorvos is an organophosphorus and organochlorine insecticide. Dichlorvos have poor permeability in grains and remain for long periods of time. There is also the problem that insects become resistant to dichlorvos.

Isothiocyanates are usually present as crystalline solids thereof. Typically, delivery of isothiocyanate fumigants is by sublimation of the solid crystals from its high vapor pressure. Isothiocyanate dissolution in sulfuryl fluoride can also be delivered. As the sulfuryl fluoride evaporates, crystals of the isothiocyanate form on the surface of the structure or product. The isothiocyanate crystals may then be sublimed in the usual manner to act as fumigants.

Other fumigants used against grain pests include acrylonitrile, carbon disulfide, carbon tetrachloride, trichloronitromethane, ethylene dibromide, ethylene dichloride, ethylene oxide and sulfuryl fluoride.

It will be noted that none of the "traditional" fumigants have ideal fumigant characteristics and phosphine will become the only registered fumigant available for agriculture in australia.

For many years, new fumigants have been sought, and the search for improved fumigants will continue undoubtedly. There is a particular pressing need to develop a multi-purpose grain treatment for use on farms that ideally should be inexpensive and easy to operate and perform, particularly in unsealed storage containers (containers) such as agricultural bins.

Disclosure of Invention

The present invention seeks to provide new fumigant compositions and methods by which it is possible to reliably control insects, rodents, mites, nematodes, fungi and their spores, bacteria, viruses, moulds and other pest biota as a viable alternative to traditional fumigants. The present invention also seeks to provide novel fumigant compositions comprising synergistically acting liquid or gas combinations which are stable when applied together and can be stored for long periods of time.

In one broad form, the present invention provides a fumigant composition comprising an alkyl formate and an isothiocyanate. That is, the present inventors have surprisingly found that alkyl formate and isothiocyanate act synergistically.

In another broad form, the invention provides a method of increasing the efficacy of an isothiocyanate comprising the step of combining the isothiocyanate with an effective amount of an alkyl formate.

In yet another broad form, the invention provides a method of increasing the efficacy of ethyl formate comprising the step of combining ethyl formate with an effective amount of an isothiocyanate.

In another broad form, the invention provides a method for improving the delivery of an isothiocyanate comprising dissolving the isothiocyanate in an alkyl formate to form a fumigant composition and vaporizing or projecting the composition.

In other broad forms, the invention provides a method of fumigation comprising applying an alkyl formate and an isothiocyanate in gaseous form or in solution to a product and/or structure and/or space.

In a preferred embodiment, the fumigant composition further comprises a diluent, excipient or carrier. The fumigant may be provided in solution or in combination with a carrier gas. Preferably, the carrier gas is an inert gas and it is also preferred that the carrier gas has a low oxygen concentration. In a preferred embodiment of the invention, the carrier gas comprises carbon dioxide or is applied in an environment containing carbon dioxide.

In preferred forms, the products include grains, seeds, meat, fruits, dried fruits, vegetables, wood, plants, cut flowers and soil.

Preferably, the products include silos or similar structures containing bulk grain (e.g., wheat) and the like, insulation killers for import agricultural and horticultural, and rooms, houses, appliances, and the like for dental, medical, and/or veterinary applications.

The fumigant composition is particularly suitable for use in open agricultural tanks and silos, but has been found to be effective in any shaped structure, vessel or container.

In a preferred embodiment, the fumigant is capable of controlling one or more of a variety of biological groups including viruses, insects, arachnids, mites, nematodes, bacteria, moulds, fungi and spores thereof.

In embodiments of the invention, the humidity and/or pressure within the environment to which the fumigant composition is applied is adjusted to control the properties of the fumigant composition (e.g. toxicity increase and/or synergistic effect).

The alkyl formates used in the compositions and methods of the present invention are preferably ethyl formate and methyl formate. In a more preferred embodiment, particularly where the food needs to be fumigated, the alkyl formate is ethyl formate. In general, ethyl formate is the preferred alkyl formate throughout the embodiments that follow. However, it is to be understood that methyl formate may also be used in many of the compositions and methods of the present invention.

The isothiocyanate used in the compositions and methods of the present invention is preferably lower alkyl, lower alkenyl, phenyl or benzyl isothiocyanate, which may optionally be substituted. More preferably, the isothiocyanate is methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl or tert-butyl, allyl, methallyl, benzyl or phenyl isothiocyanate. Optional substituents for alkyl, benzyl or phenyl groups may include halogen, including chlorine, fluorine, bromine or iodine, methyl or ethyl, methoxy or ethoxy, cyano or nitro (ntiro). Most preferably, the isothiocyanates are methyl isothiocyanate and allyl isothiocyanate. In general, methyl isothiocyanate is the preferred isothiocyanate throughout the embodiments that follow. However, it is to be understood that allyl isothiocyanate and other related isothiocyanates can also be used in the compositions and methods of the present invention. For example, allyl isothiocyanate has better food tolerance and its use is less of a problem in some applications to food.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Brief Description of Drawings

The invention will be more fully understood from the following detailed description of preferred but non-limiting embodiments of the invention, of various examples of experimental methods of the inventor summarizing the invention, and the accompanying drawings, in which:

FIG. 1 graphically illustrates the stability of formulations of ethyl formate and methyl isothiocyanate stored at 25℃ for two months over a period of one day, one month, and two months. M/Mo is the percentage of the original fumigant present after different storage times.

FIG. 2 is a graph showing the toxicity of fumigants of ethyl formate alone and ethyl formate plus methyl isothiocyanate when fumigated at 25 ℃ for 24 hours against adult rice weevils (Sitophilus oryzae) as compared.

FIG. 3 is a graph showing the comparison of the toxicity of fumigants of ethyl formate alone and two concentrations of ethyl formate plus methyl isothiocyanate on rice weevil mixed-age cultures (eggs, larvae and pupae) by fumigation at 25 ℃ for 6 hours.

FIG. 4 is a graph showing the comparison of the toxicity of fumigants of ethyl formate alone and ethyl formate plus methyl isothiocyanate in combination with the fumigation of rice weevil pupae at 25 ℃ for 6 hours.

FIG. 5 is a graph showing the comparison of rice weevil toxicity to pupal stages of two concentrations of fumigants ethyl formate alone and ethyl formate plus methyl isothiocyanate when fumigated at 25 ℃ for 24 hours.

Fig. 6 shows schematically a polyvinyl chloride cylinder with a diameter of 75.8L (24.2 cm and h 165cm) filled with 52kg wheat. Wheat samples were taken from different locations in the cylinder after 7 days without aeration to show the residual concentration of ethyl formate and methyl isothiocyanate.

FIG. 7 is a graph showing the concentration of ethyl formate and methyl isothiocyanate in a wheat cylinder (95% filling rate) in a 7-day fumigated state at room temperature.

FIG. 8 shows, in a schematic representation, 1.35m of a 1-ton wheat load³(. 100cm and h 172 cm).

FIG. 9 graphically represents the concentration of ethyl formate and methyl isothiocyanate in a 1 ton wheat bin (95% fill) at room temperature for 7 days of fumigation. (● is the concentration of ethyl formate and ≈ is the concentration of Methyl Isothiocyanate (MITC)).

FIG. 10 is a schematic representation of the application of a composition of ethyl formate plus methyl isothiocyanate to grain from a bin during unloading onto a truck via an auger.

Detailed Description

Ethyl formate is a naturally occurring substance that is commonly found in soil, oceans, and vegetables. It is present in all kinds of plant and animal products, such as fruits and vegetables, beer, wine and alcohol, tuna, meat, muscle, cheese and bread. Some cereals and cereals such as barley have detectable amounts of ethyl formate present at concentrations up to 1 mg/kg. Ethyl formate is a odorless liquid (boiling point 54 ℃ C.) and has a pleasant aromatic odor. It can be prepared by reacting ethanol, which is a naturally occurring chemical, with formic acid. When used as fumigants, ethyl formate is hydrolyzed or metabolized back to these naturally occurring chemicals. Formic acid and ethanol may be present in the grain at fairly high levels, in amounts up to 300mg/kg or more.

Humans are often exposed to the naturally occurring ethyl formate in a variety of foods, and it is therefore not surprising to consider ethyl formate as having low toxicity to mammals when contacted by diet for extended periods. Furthermore is the usual metabolic pathway for the decomposition of ethyl formate into formic acid and ethanol by hydrolysis, which leads to a higher occupational contact limit for ethyl formate as a substitute for phosphine or methyl bromide.

Ethyl formate has proven to have a very rapid action against insects storing grains, which makes it useful for rapid disinfestation of stored products including grains and fruits, as well as vegetable treatment.

Methyl formate may also be used in the compositions and methods of the present invention. It is slightly more potent than ethyl formate as a fumigant, however, the use of methyl formate in foods and foodstuffs is undesirable due to the toxicity of methanol, one of its decomposition products.

Surprisingly, the inventors of the present invention found that compositions of alkyl formate and isothiocyanate show significantly improved grain kill rates in shorter times and at lower concentrations when compared to the expectations of alkyl formate alone, toxicity of isothiocyanate alone or simple additive mixtures of alkyl formate and isothiocyanate.

The amount of isothiocyanate needed to impart an improved effect on the alkyl formate fumigant formulation is relatively small. In a preferred embodiment, the ratio of alkyl formate to isothiocyanate is not greater than 40% w/w isothiocyanate, more preferably not greater than 20% w/w isothiocyanate, more preferably not greater than 10% w/w isothiocyanate and more preferably about 5% w/w isothiocyanate. Lower concentrations of isothiocyanate are preferred to minimize problems associated with isothiocyanate toxicity to mammals and residues thereof. Any minor amount of isothiocyanate may be used provided that it provides a synergistic effect which is typically observed to begin at about 0.5% w/w isothiocyanate.

The fumigant composition of the present invention is prepared by dissolving isothiocyanate in alkyl formate. Ethyl formate and methyl isothiocyanate were found to be stable when formulated and stored at 25 ℃ for two months. Similar results were found for the combination of ethyl formate and methyl formate with different isothiocyanates. This allows for bulk formulation of fumigant compositions and transport to the site of administration. It will also be appreciated that the components may be intimately mixed on site prior to fumigation or applied simultaneously or sequentially to the product or structure.

The insect species studied were rice elephant laboratory strains, provided as eggs, larvae, pupae or adults and mixed-age cultures thereof in wheat stored in bulk. At a concentration of 5.9mg/L, ethyl formate alone was found to be inactive against adult rice weevils by fumigation at 25 ℃ for 24 hours. In comparison, the addition of 5% methyl isothiocyanate resulted in 99% mortality of adults under the same conditions. The composition supplemented with 5% methyl isothiocyanate also showed a strong synergistic effect on the whole mixed-age rice-elephant culture profile compared to other concentrations of ethyl formate.

Residual studies on fumigated wheat over 7 days found that with negligible amounts of methyl isothiocyanate and ethyl formate residues, the non-aerated fumigant dropped to background values.

The amount of fumigation and germ length were determined on representative samples taken before and after fumigation. The ethyl formate/methyl isothiocyanate formulation was found not to affect barley, wheat and sorghum sprouting (7 days old) nor germ length. The formulations of the present invention also do not affect the sprouting of oats, corn, canola and legumes.

The improved effect of alkyl formates and isothiocyanates is also evident in formulations mixed with a carrier gas. The carrier gas may be an inert gas and may conveniently have a low oxygen concentration. Carbon dioxide is the preferred carrier gas, and it is believed that carbon dioxide increases the respiration rate of insects and other biological groups and will therefore increase the rate at which ethyl formate and methyl isothiocyanate enter the respiratory system of the pest. The carrier gas has the additional advantage of lowering the flash point of the ethyl formate vapor and is generally considered nonflammable when ethyl formate is present at a concentration of no more than about 16-19%.

The ethyl formate plus isothiocyanate formulation of the present invention may be present in liquid carbon dioxide or as a liquid in gaseous carbon dioxide or other such carrier gas familiar to those skilled in the art. For example, a 16.7% by weight mixture of 95: 5 ethyl formate plus methyl isothiocyanate in 83.3% by weight carbon dioxide contained in a pressure cylinder may be applied as a gas to a fumigated product or structure (see, for example, the method of WO 03/061384). Carbon dioxide has the additional advantage of acting as a solvent/propellant to disperse the compound as aerosol particles. Flow-through technology may further facilitate a fumigation process that includes a carrier gas. Allyl isothiocyanate, methyl isothiocyanate or any other suitable isothiocyanate may be used in combination with the ethyl formate.

Typically, the carbon dioxide mixture is applied through a spray nozzle and the amount applied is calculated to meet the product or structure being treated. It is also possible to add the ethyl formate plus isothiocyanate formulation to gaseous carbon dioxide and to vaporize and mix the liquid formulation with the carbon dioxide prior to or during administration. As with all administration regimens, the fumigant formulation may be administered over a period of time or at intervals to complete a dose or to achieve (top up) a previous dose.

Other fumigation methods include low flow gaseous fumigation, low pressure gaseous fumigation, high pressure gaseous fumigation, spraying fumigants in solution and dipping the product in fumigants and solution. This list is not exhaustive and the administration of the synergistic formulation of the present invention can be varied to best suit the fumigation method, as can be determined by one skilled in the art. The formulation may be applied as a liquid, gas or vapour dissolved in a carrier gas or by adsorption or adsorption chemistry. One skilled in the art will appreciate that fumigation of the product may be achieved by spraying the product with a liquid containing the formulation, or the formulation may be poured onto or into the product to coat it or drip from it. In the application of the fumigant of the present invention, a probe having a small hole may be inserted into the grain bin. Air or any other suitable gas may be bubbled or forced through the product or structure to vaporize and/or disperse the fumigant. Contact with the fumigant may be maintained by continuous or intermittent administration or as a one-time treatment.

The two active ingredients, alkyl formate and isothiocyanate, may be administered as formulations optionally intimately mixed with a solid, liquid or gaseous carrier and may be administered simultaneously or sequentially within a short period of time sufficient to achieve a synergistic result.

In a highly preferred application, the formulations of the invention are prepared by dissolving a solid isothiocyanate in a liquid alkyl formate as a binary active mixture. Without wishing to be bound by theory, it is believed that the partitioning of the isothiocyanate into the alkyl formate allows the isothiocyanate and alkyl formate to vaporize together. It is believed that the formulation provides a more uniform distribution of the isothiocyanate in the fumigated structure, space or product and a better adsorption gradient in the grain than the crystalline isothiocyanate itself. This allows better access to the insect or pest biota, especially the Rhyzopertha dominica (Rhyzopertha dominica) and rice weevil, of various internal stages (internal stages) in products such as cereals.

Successful application can also be carried out by mixing the gas stream containing the alkyl formate with a volatile stream of isothiocyanate. In these cases, the isothiocyanate is typically at least preheated to effect volatilization of the solid. The streams may be mixed prior to application to the product or structure or applied separately and mixed therein. The vaporization and formation of the synergistic fumigant mixture of the present invention can also be achieved by passing a stream of ethyl formate gas over a heated bed of solid isothiocyanate. These and other methods of mixing and/or applying fumigants familiar to those skilled in the art to achieve the desired results are within the scope of the present invention.

At the end of fumigation, ethyl formate is naturally decomposed, usually by hydrolysis, into ethanol and formic acid. Methyl formate decomposes into methanol and formic acid. In addition, nonventilated isothiocyanate residues were found to be reduced to acceptable levels. Positive steps may also be taken to remove residual fumigant by natural ventilation or by rinsing the product with a clean stream of air, although this is not generally required.

One skilled in the relevant art will appreciate that the amount of fumigant provided to the fumigant volume varies depending on the level of infestation and type of infestation present. The required fumigant dose is then calculated using a combination of fumigant concentration and contact time. Generally lower concentrations require increased duration, while higher concentrations are suitable for shorter durations.

The ethyl formate may be provided as Eranol by Orica^®And (4) obtaining. Likewise, methyl formate can also be obtained. Isothiocyanates are available from Sigma Aldrich or as a component of mustard oil from brassica rapa.

The formulation of the present invention allows for successful fumigation of products at sub-lethal concentrations of ethyl formate alone. Additionally or alternatively, the formulation may be found to be effective in a shorter application time and/or at a lower application temperature than the isothiocyanate in the absence of the alkyl formate.

The improved formulation was found to be about 2-3 times more efficacious than ethyl formate alone and about 4-5 times more efficacious than methyl isothiocyanate alone.

The fumigant formulations of the present invention may also advantageously comprise additional fumigants, provided that they do not react with or are not harmful to alkyl formates or isothiocyanates.

If different types of insects or pest biota are to be controlled, the concentration is preferably associated with the most difficult insect or pest to control. Products such as seeds, cereals, fruits or agricultural products can be fumigated with their containers such as transport means (ships, rail wagons, trucks), rooms and buildings (churches, museums, mills), storage rooms (barns, silos or containers) and kegs (drums, pails, etc.). The fumigant composition may advantageously be used in a sealed or encapsulated confinement (enclosure), however it is particularly suitable for grain storage in unsealed silos and bins.

Preferably, when a ethyl formate formulation is used as a fumigant of cereals, the cereal or product to be treated is at a temperature of 15 ℃ or higher. The field tests show that the ethyl formate formulation of the present invention exhibits superior activity as a fumigant for an unsealed agricultural tank as compared to the use of ethyl formate alone. Unlike phosphine, which takes several days to kill insects, the ethyl formate formulations of the present invention rapidly kill insects and biota in about 20 hours or less. The formulation is convenient to transport and store and easy to apply. The synergistic formulation of the present invention allows the use of lower concentrations of ethyl formate while having better control and higher mortality rates for a wide variety of species and life stages of pests. The ethyl formate formulation of the present invention resulted in a suitable fast lethal alternative to methyl bromide that will be phased out in developed countries since 2005.

The inventors of the present invention have conducted many experiments to demonstrate the improved effects of isothiocyanates and alkyl formates as fumigant formulations. Some of these non-limiting experiments are detailed in the examples below.

Examples

1. Stability testingIs especially suitable for the treatment of diabetes

The stability of ethyl formate (EtF) and Methyl Isothiocyanate (MITC) as fumigant formulations stored at 25 ℃ was evaluated over 1 day, 1 month and 2 months. Table 1 below shows the percentage of original fumigant present (M/Mo) after different storage times. This is also represented graphically in fig. 1. The results show that ethyl formate and methyl isothiocyanate are stable when stored for two months after formulation.

TABLE 1 stability of Ethyl formate and methyl isothiocyanate formulations (M/Mo)

	1 day	1 month	2 months old
				EtF	100	102	98.5
MITC	100	98	101.5

2. Toxicity Studies

Toxicity studies of adult rice weevils were performed on ethyl formate alone versus ethyl formate and ethyl isothiocyanate at 25 ℃ and fumigated for 24 hours. Toxicity studies were performed at concentrations of 5.9mg/L and 11.8 mg/L. The results are shown in table 2 below and fig. 2.

TABLE 2 mortality study of adult rice weevils with ethyl formate alone and methyl formate and isothiocyanic acid methyl ester (mortality 100%)

5.9mg/L

11.8mg/L

EtF	0	48
			EtF+MITC	99	100

Toxicity studies showed that adult rice weevils were unaffected by fumigation with ethyl formate at a concentration of 5.9mg/L for 24 hours at 25 ℃. After addition of 5% methyl isothiocyanate, 99% adult rice weevil mortality was observed, indicating a very significant synergy between ethyl formate and methyl isothiocyanate. Doubling the fumigant concentration to 11.8mg/L showed 48% mortality with ethyl formate alone compared to 100% mortality with ethyl formate/methyl isothiocyanate formulations of the present invention.

Table 3 compares the toxicity of mixed age cultures of ethyl formate alone and ethyl formate plus methyl isothiocyanate on rice weevils (eggs, larvae and pupae) after fumigation at 25 ℃ for 6 hours. These results are graphically represented in fig. 3.

TABLE 3 eclosion adult (emerging adult) study of mixed age cultures of rice weevils using ethyl formate alone and ethyl formate plus methyl thiocyanate

	Control group	EtF	EtF+MITC
				67.4mg/L	100	27	3
101.1mg/L	100	5	0

The results show that ethyl formate alone as fumigant against rice weevil mixed age cultures at a concentration of 67.4mg/L limited the eclosion adult population to 27% of the control samples. In comparison, the same concentration of ethyl formate plus ethyl thiocyanate fumigant composition of the invention significantly reduced the eclosion adult population to 3% of the control. Ethyl formate alone at a higher concentration of 101.1mg/L further reduced the eclosion adult population to 5% of the control. In comparison, ethyl formate plus methyl isothiocyanate preparation at this high concentration completely prevented mixed-age cultures from reaching the adult stage.

Table 4 compares the toxicity of ethyl formate alone versus ethyl formate plus methyl isothiocyanate on rice weevil pupae after fumigation at 25 ℃ for 6 hours. These results are graphically represented in fig. 4.

TABLE 4 study of eclosion imagoes of rice weevils pupae by fumigation of ethyl formate alone with ethyl formate plus methyl isothiocyanate for 6 hours (% eclosion imagoes)

	Control group	EtF	EtF+MITC
				67.4mg/L	100	24	1
101.1mg/L	100	12	0

The results show that ethyl formate alone as a fumigant against rice weevil pupae at a concentration of 67.4mg/L limited the eclosion adult population to 24% of the control samples. In comparison, the same concentration of the ethyl formate plus methyl isothiocyanate fumigant composition of the present invention significantly reduced the eclosion adult population to only 1% of the control. Ethyl formate alone at a higher concentration of 101.1mg/L further reduced the eclosion adult population to 12% of the control group. In comparison, the ethyl formate plus methyl isothiocyanate preparation completely prevented the pupae from reaching the adult stage at this higher concentration.

Table 5 compares the toxicity of ethyl formate alone versus ethyl formate plus methyl isothiocyanate on rice weevil pupae after 24 hours fumigation at 25 ℃. These results are graphically represented in fig. 5.

TABLE 5 study of eclosion imagoes of rice weevils pupae by fumigation of ethyl formate alone with ethyl formate plus methyl isothiocyanate for 24 hours (% eclosion imagoes)

	Control group	EtF	EtF+MITC
				34.8mg/L	100	19	0
67.4mg/L	100	9	0

The results show that ethyl formate alone as a fumigant against rice weevil pupae at a concentration of 34.8mg/L limited the eclosion adult population to 19% of the control sample, and to 9% at a concentration of 67.4 mg/L. In comparison, both ethyl formate and methyl isothiocyanate formulations completely prevented pupae from reaching the adult stage at both concentrations.

3.54kg wheat drum test

Wheat cylinders were fumigated for seven days without aeration using ethyl formate plus methyl isothiocyanate in a ratio of 95: 5 (w: w). The cylinder was made of polyvinyl chloride, had a volume of 75.8L (24.2 cm and h 165cm) and was filled with 52kg of wheat, shown in fig. 6. The ethyl formate/methyl isothiocyanate formulation was applied to wheat at a rate of 80g/t and subjected to low recirculation air (1 aeration/hour).

A comparison of ethyl formate and methyl isothiocyanate residues in fumigated wheat at different positions of the cylinder is also shown in figure 6. The wheat is not fumigated for seven days. Ethyl formate and methyl isothiocyanate fumigants were found to permeate the entire barrel of wheat and achieved a uniform distribution of fumigants. After seven days without aeration, the ethyl formate residue was reduced to 37ppm and the isothiocyanic acid ethyl ester residue was reduced to 0.06ppm and less.

The concentrations of ethyl formate and methyl isothiocyanate were found to decrease rapidly at an exponential rate in a wheat cylinder (99% fill) during 7 days of fumigation at room temperature. Figure 7 depicts the decrease in concentration of each fumigant ingredient over time during a seven day fumigation trial.

These studies have been extended to Tribolium castaneum (Tribolium castaneum) and khaki insects. Bioassay studies showed that all phases of these insects tested were killed.

4.1 ton box test

The wheat boxes were not fumigated for seven days using ethyl formate plus methyl isothiocyanate in a ratio of 95: 5 (w: w). The metal box has a thickness of 1.35m³And 1 ton of wheat was charged. The tank is shown in fig. 8. The wheat was dosed with the ethyl formate/methyl isothiocyanate formulation at 80g/t, subjected to low recirculation air (1 ventilation/hour), and fumigated for seven days.

The concentrations of ethyl formate and methyl isothiocyanate were found to decrease rapidly at an exponential rate in a wheat cylinder (95% fill) during 7 days of fumigation at room temperature. Figure 9 depicts the decrease in concentration of each fumigant ingredient over time during a seven day fumigation trial.

These studies extend to the tribolium castaneum and the khaki insect. Bioassay studies showed that all phases of these insects tested were killed.

5.4 ton unload test

During unloading, wheat was treated/fumigated at a rate of 160g/t using ethyl formate plus methyl isothiocyanate in a ratio of 95: 5 (w: w). The treated wheat was then transferred by auger into a 4 ton truck trailer and then covered and stored overnight (see fig. 10). The concentrations of ethyl formate and methyl isothiocyanate in the wheat drawers (100% fill) were found to decrease rapidly at an exponential rate at 20 ℃ during overnight fumigation. The next day, the concentration of each fumigant component was found to decrease below TLV and all tribolium castaneum, khaki and rice weevil adults were killed.

On-site testing of 5.55 ton silos

The wheat silo is not fumigated by ventilation by using ethyl formate and methyl isothiocyanate or ethyl formate and allyl isothiocyanate in a ratio of 95: 5 (w: w). The silo has a capacity of 55 tons and is filled with 50 tons of grains. Wheat was administered EtF + MITC or EtF + AITC at a rate of 80g/t, subjected to low recirculation of air (1 ventilation/hour), and fumigated for seven days.

The two fumigant formulations were found to be effective in killing all tested insects without having an effect on the germination and seed colour of the treated wheat. The residue after seven days of unvented contact was reduced to the background values of ethyl formate and methyl or allyl isothiocyanate. The results are shown in table 6 below.

Table 6. mortality study of pest biota using ethyl formate plus methyl isothiocyanate or ethyl formate plus allyl isothiocyanate in silo volumes of wheat.

Location of a site	Canberra	Canberra	Brisbane
				Product(s)	Wheat (Triticum aestivum L.)	Wheat (Triticum aestivum L.)	Wheat (Triticum aestivum L.)
Silo capacity	55t	55t	50t
				Amount of grain	50t	50t	50t
Temperature of grain	20-23℃	20-23℃	22-24℃
				Preparation	EtF+MITC(95∶5，v/w)	EtF+AITC(95∶5，v/w)	EtF+MITC(95∶5，v/w)
Dosage form	80g/t grain	80g/t grain	80g/t grain
				Administration of	Dumping from the upper part of the silo	Dumping from the upper part of the silo	Dumping from the upper part of the silo
Recycle of	1 air change/hour	1 air change/hour	1 air change/hour
				Biological assay results	100% kill all stages of insects: tripsammophytes castanea (T.variabilie) Guassamick Diagnosticus Dianus (O.surinamensi)s)	100% kill all stages of insects: tribary griseus bark beetle-Guassius saw-Guassamia	100% kill all stages of insects: chitosan beetle-grain elephant
Quality of wheat	Has no influence on the occurrence and seed color of the treated wheat	Has no influence on the occurrence and seed color of the treated wheat	Has no influence on the occurrence and seed color of the treated wheat
				Residue is remained	EtF and MITC decreased to background values for 7 days without aeration contact.	EtF and AITC decreased to background values for 7 days without aeration contact.	EtF and MITC decreased to background values for 7 days without aeration contact.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in the specification, individually or collectively, and any and all combinations of any two or more of said steps or features.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that prior art forms part of the common general knowledge in the field of endeavour.

Claims (27)

1. A fumigant composition comprising an alkyl formate and an isothiocyanate.

2. A fumigant composition of claim 1, wherein about 60 to 99.5 parts w/w of alkyl formate to about 40 to 0.5 parts w/w of isothiocyanate are present in the composition.

3. A fumigant composition of claim 2, wherein about 95 parts w/w of alkyl formate to about 5 parts w/w of isothiocyanate are present in the composition.

4. A fumigant composition of claim 1, further comprising a diluent, excipient or carrier.

5. A fumigant composition of claim 1, wherein the alkyl formate is methyl formate.

6. A fumigant composition of claim 1, wherein the alkyl formate is ethyl formate.

7. A fumigant composition of claim 1, wherein the isothiocyanate is an optionally substituted lower alkyl, lower alkenyl, phenyl or benzyl isothiocyanate.

8. A fumigant composition of claim 7, wherein the isothiocyanate is selected from methyl isothiocyanate and allyl isothiocyanate.

9. A fumigant composition of claim 1, wherein the alkyl formate is ethyl formate and the isothiocyanic ester is methyl isothiocyanate.

10. A fumigant composition of claim 1, wherein the alkyl formate is ethyl formate and the isothiocyanate is allyl isothiocyanate.

11. A method of delivering an isothiocyanate to a product, structure or space by applying a fumigant mixture of isothiocyanates in an alkyl formate to the product, structure or space and vaporizing the fumigant mixture.

12. The method of claim 11 wherein the product is stored grain or the structure or space contains or contains stored grain.

13. The method of claim 12, wherein the fumigant mixture kills internal stages of pest biota in the stored grain.

14. A method of increasing the efficacy of an isothiocyanate as a fumigant comprising the step of combining the isothiocyanate with an alkyl ester.

15. A method of increasing the efficacy of an alkyl formate as a fumigant comprising the step of combining the alkyl formate with an effective amount of an isothiocyanate.

16. A fumigation method comprising the step of applying to a product and/or structure and/or space an effective amount of an alkyl formate and an isothiocyanate in gaseous form or in solution.

17. The method of claim 11, 14, 15 or 16, wherein the alkyl formate and isothiocyanate are in solution or combined with a carrier gas.

18. The method of claim 17, the carrier gas is an inert gas having a low oxygen concentration.

19. The method of claim 18, wherein the carrier gas comprises carbon dioxide.

20. The method of claim 16, wherein the product is selected from the group consisting of grain, seed, meat, fruit, dried fruit, vegetables, wood, plants, cut flowers, and soil.

21. The method of claim 16, wherein the structure and/or space is an agricultural bin, silo, container, room or house, flour or rice mill or food processing plant, supermarket, museum.

22. The method of claim 21, wherein the structure is open.

23. The method of claim 16 for controlling one or more of a plurality of biological populations including viruses, insects, spiders, psocids, mites, nematodes, bacteria, molds and fungi and their spores.

24. The method of claim 11, 14, 15 or 16, wherein the alkyl formate is methyl formate.

25. The method of claim 11, 14, 15 or 16, wherein the alkyl formate is ethyl formate.

26. The method of claim 11, 14, 15 or 16 wherein said isothiocyanate is optionally substituted lower alkyl, lower alkenyl, phenyl or benzyl isothiocyanate.

27. The method of claim 26 wherein the isothiocyanate is selected from the group consisting of methyl isothiocyanate and allyl isothiocyanate.