Background of the invention The pine weevil, Hylobius abietis, kills through its gnawing on the bark a large pro- portion of the conifer saplings that are planted after felling. The damage costs Swedish forestry hundreds of millions Swedish crowns yearly (Weslien 1998). The pine weevil is, therefore, one of the economically most important insects in Sweden. The species is known as a serious noxious insect in large parts of Europe and Asia. In North America there are some closely related species with a similar way of living (Hylobius pales, Hylobius congener, and Pachylobius picivorus).

The damage by the pine weevil could to a certain degree be reduced by a fallow pe- riod, soil scarification and regeneration beneath shelterwood trees. The fallow period should be avoided because of production loss and problems with competing vegeta- tion. Soil scarification and regeneration beneath shelterwood are silvicultural methods that currently are further developed, and that in many areas could be included as a part of the management of the pine weevil problem (Orlander & Nordlander 1998). How- ever, further protection of the saplings is needed in most places. Different ways of me- chanical protection are presently tested but there is not yet any method really working in practice (Orlander & Petersson 1998).

Since a long time, the pine weevil problem has mainly been managed by immersion or spraying the saplings with a relatively persistent insecticide (Langstrom 1998). At pre- sent, the synthetic pyrethroid permethrin is allowed for this purpose in Sweden. How- ever, the Swedish National Chemicals Inspectorate has the intention to prohibit this

treatment of saplings after the year 2004 because of environmental reasons. Possibly the other Nordic countries will also follow this example. Therefore, it is very urgent to find alternatives to protection treatment with insecticides.

Some alternatives to insecticides have been described in the literature such as insect repellents and the use thereof. For example, Viktorov-Nabokov (1980) describes methyl-4-hydroxybenzoate as a blood sucking mosquito repellent. SE 7709013-2 de- scribes the use of a composition comprising halogen substituted phenols and phenol ethers designed for conifer sapling protection against noxious insects. No publications describe the use of the compounds according to the invention for conifer sapling pro- tection against insect attack, wherein the insect species belong to the beetle (Coleop- tera) family Curculionidae.

There is strong evidence that plants have evolved defense systems against herbivores and pathogenes, and that these systems to a large extent are based on the production of secondary metabolites (Rosenthal 1986, Harborne 1988 and references cited therein, Sunnerheim-Sjoberg, 1991, Daurade-Le Vaguresse et al. 1992, Suga et al. 1993). Even high priority food plants produce defense compounds against herbivores-otherwise the plant would risk to be overbrowsed. So, although the polyphagous pine weevil pre- fers pines to a multitude of other plant species (Eidmann 1974), pines can be expected to contain antifeedants against pine weevils. However, different species of pines and different parts of a pine tree may contain varying amounts of defense compounds.

Comparative tests have shown that pine weevils feed less on bark from Lodgepole pine, Pinus contorta L, than on bark from Scots pine, P. sylvest7tis Dougl., and this result promoted us to look for compounds possessing antifeedant activity derived from P. contort. Scots pine is the most abundant pine in Sweden, while Lodgepole pine has been introduced from North America and planted on large areas in northern Sweden.

Bioassays of fractionated extracts of Lodgepole pine bark showed strong gnawing- inhibitory effect for a fiaction containing mainly compounds no. 1 and 15. Further bioassays showed that these compounds, as well as several similar substances, have a

significant gnawing-inhibiting effect. The toxicity of these substances is low. The risk of resistance development towards the substances is insignificant due to the fact that saplings constitute a small part of the pine weevil diet (Nordlander 1998).

Summary of the invention The present invention relates to the use of certain cinnamate and/or phenylpropanoate derivatives for conifer sapling protection against insect attack. It also relates to the use of a composition for conifer sapling protection against insect attack. Finally, it relates to a compound of formula (I).

Detailed description of the invention One object of the present invention is the use of at least one compound for conifer sapling protection against insect attack, wherein the insect species belong to the beetle (Coleoptera) family Curculionidae (including subfamilies Curculioninae and Scolyti- nae), particularly species of the genera Hylobius, Pachylobius and Hylastes, specifi- cally the species Hylobius abietis, Hylobius pinastri, Hylobius pales, Hylobius conge- ever, Pachylobius picivorus, Hylastes brunnens and Hylastes cunicularius, character- ised in that the compounds are selected from the following compounds with formula I : Formula I wherein

Rl, R2, R3, R4, and Rs each independently stand for -hydrogen; -hydroxy ; -a Cl-C6-alkyl group ; -a C2-C6-alkenyl group; - a C1-C6-alkoxy group, preferably methoxy or 1-butoxy ; -a C2-C6-alkenoxy group; -halogen, preferably bromo; R6 and R7 each independently stand for -methylene; -one or two hydrogens; -one hydroxy and optionally one hydrogen ; -one Cl-C6-alkyl group, preferably methyl, and optionally one hydrogen; -one C2-C6-alkenyl group, and optionally one hydrogen; -one halogen, preferably bromo, and optionally one hydrogen; R8 stands for -hydrogen; -a Cl-C6-aLkyl group, preferably methyl, ethyl, n-propyl, isopropyl, 1-butyl or 2- butyl; -a C2-C6-alkenyl group; ~~~~ stands for a single or a double carbon-carbon bond; as well as esters and salts thereof.

Another object of the present invention is the use of a composition for conifer sapling protection against insect attack, wherein the insect species belong to the beetle (Cole- optera) family Curculionidae (including subfamilies Curculioninae and Scolytinae), particularly species of the genera Hylobius, Pachylobius and Hylastes, specifically the species Hylobius abietis, Hylobius pinastri, Hylobius pales, Hylobius congener, Pachylobius picivorus, Hylastes brunnesus and Hylastes cunicularius, characterised in that it comprises at least one of the following compounds with Formula I : Folmula I

wherein RI, R2, R3, R4, R5, R6, R7, Rg, and--are as defined above, pure or in a solvent, with or without a suitable carrier such as wood, cellulose, wood-flour, straw, cork, cane, lignin, lignocellulose, rubber, gum, leather or skin, milled carbon, fats or waxes of animal, vegetable, or synthetic origin, natural resins of animal or vegetable origin, plastic, organic polymers such as polyvinyl acetate, polyacrylates, polyvinyl chloride, chlorinated polyethylene, polyols such as polyethylene glycol, synthetic or natural latexes, silicone polymers or resins, silicates, pumice, silica, or any mixture thereof.

Preferred compounds are those of Formula I with the exception of methyl 3', 4'- dimethoxycinnamate.

Another object of the invention is a compound of Formula I, wherein R3 is methoxy ; RI, R2, 84, and R5 are hydrogen; R6 and R7 are both two hydrogens; and R8 is isopro- pyl.

A suitable solvent is selected from the group consisting of Cl-C6-alkohols and Cl-C6- aRyl esters of a Cl-C6-alkanoic acid, preferably methyl acetate and methanol.

As used in this application : a) the term"Cl-C6-alkyl"refers to a saturated, straight or branched chained alkyl radi- cal containing from 1 to 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, 1-butyl, 2-butyl, t-butyl, n-pentyl, n-hexyl, etc;

Thus, any alkyl containing 1,2,3,4,5, or 6 carbon atoms could be used.

For parts of the range"Cl-C6-alkyl"all subgroups thereof are contemplated such as Ci-Cs-alkYl, C1-C4-alkyl, C1-C3-alkyl, C1-C2-alkyl, C2-C6-alkYl, C3-C6-alkyl, C2-C5- alkyl etc ; b) the term"C2-C6-allcenyl"refers to an unsaturated, straight or branched chained alkenyl radical containing from 2 to 6 carbon atoms, such as vinyl, 1-propenyl, 2- propenyl, 1-butenyl, 1-pentenyl, 1-hexenyl, etc; Thus, any alkyl containing 2,3,4,5, or 6 carbon atoms could be used.

For parts of the range"C2-C6-alkenyl"all subgroups thereof are contemplated such as C2-C5-alkenyl, C2-C4-alkenyl, C2-C3-alkenyl, C2-C6-alkenyl, C3-C6-alkenyl, C4- Cs-alkenyl etc; c) the term "C1-C6-alkoxy" refers to a saturated, straight or branched chained alkoxy radical containing from 1 to 6 carbon atoms, such as methoxy, ethoxy, n-propoxy, isopropoxy, 1-butoxy, 2-butoxy, t-butoxy, n-pentoxy, n-hexoxy, etc; Thus, any alkoxy containing 1,2,3,4,5, or 6 carbon atoms could be used.

For parts of the range"Cl-C6-alkoxy"all subgroups thereof are contemplated such as Cl-C5-alkoxy, C1-C4-alkoxy, C1-C3-alkoxy, C1-C2-alkoxy, C2-C6-alkoxy, C3-C6- alkoxy, C2-C5-alkoxy etc; d) the term"C2-C6-alkenoxy"refers to an unsaturated, straight or branched chained alkenoxy radical containing from 2 to 6 carbon atoms, such as vinyloxy, 1- propenoxy, 2-propenoxy, 1-butenoxy, 1-pentenoxy, 1-hexenoxy, etc; Thus, any alkyl containing 2,3,4,5, or 6 carbon atoms could be used.

For parts of the range"C2-C6-alkenoxy"all subgroups thereof are contemplated such as C2-C5-alkenoxy, C2-C4-alkenoxy, C2-C3-alkenoxy, C2-C6-alkenoxy, C3-C6- alkenoxy, C4-Cs-alkenoxy etc; e) the term"Cl-C6-alcohol"refers to a saturated, straight or branched alkyl alkohol and containing 1-6 carbon atoms, such as methanol, ethanol, n-propanol, isopropa- nol, n-butanol, tert-butanol, n-pentanol, n-hexanol, etc; and f) the term"Cl-C6-alkyl ester of a Cl-C6-alkanoic acid"refers to a saturated, straight or branched alkyl ester and containing 1-6 carbon atoms of a saturated, straight or branched alkanoic acid and containing 1-6 carbon atoms, such as methyl formiate,

ethyl formiate, isopropyl formiate, methyl acetate, ethyl acetate, ethyl propanoate, ethyl butyrate, ethyl valerate, ethyl hexanoate, etc.

It should be noted that both E-and Z-isomers of the compounds, optical isomers, as well as mixtures thereof, and all isotopes are included within the scope of the inven- tion. By the expression"isotopes"is meant all compounds with naturally occurring isotopes such as all possible deuterium and 13C-isotopes of the compounds according to the invention.

It should be noted that both esters and salts of the compounds according to the inven- tion are included within the scope of the invention. As examples of esters of the com- pounds are intended e. g. methyl, ethyl, n-propyl, isopropyl, 1-butyl, tert-butyl and n- pentyl esters. As examples of salts of the compounds are intended in particular envi- ronmentally acceptable acid and base addition salts.

The expression"environmentally acceptable acid addition salts"are intended to be any non-toxic organic or inorganic acid addition salt of the base compounds with the for- mula I. Examples of illustrative inorganic acids that form suitable salts are hydrochlo- ric acid, hydrobromic acid, sulphuric acid, phosphoric acid and acid metal salts such as sodium monohydrogen ortophosphate and potassium hydrogensulphate. Examples of illustrative organic acids that form suitable salts are mono-, di-and tricarboxylic acids.

Examples of such acids are acetic acid, glycolic acid, lactic acid, pyruvic acid, malonic acid, succinic acid, glutaric acid, fumaric acid, malic acid, tartaric acid, citric acid, ascorbic acid, maleic acid, hydroxymaleic acid, benzoic acid, hydroxybenzoic acid, phenylacetic acid, cinnamic acid, salicylic acid, 2-phenoxybenzoic acid, and sulphonic acids such as p-toluenesulphonic acid, methanesulphonic acid and 2-hydroxyethane- sulphonic acid. Such salts could either be in hydrated or anhydrous form. The acid ad- dition salts of these compounds are generally water soluble and different hydrophilic organic solvents and, that compared to the free base forms thereof, generally display higher melting points.

The expression"environmentally acceptable base salts"are intended to be any non- toxic organic or inorganic base addition salt of the base compounds with the formula I.

Examples of illustrative inorganic bases that form suitable salts are alkali and earth alkali metal hydroxides and carbonates such as sodium hydroxide, sodium carbonate, potassium hydroxide, potassium carbonate, calcium hydroxide, calcium carbonate, magnesium hydroxide, magnesium carbonate and ammonia. Examples of illustrative organic bases that form suitable salts are methylamine, dimethylamine, trimethylamine and picoline. Either mono-or dibasic salts could be formed with such compounds. The base addition salts of these compounds are generally water soluble and different hy- drophilic organic solvents and, that compared to the free base forms thereof, generally display higher melting points.

Examples of compounds with Formula I are listed below i e the compounds 1-21.

1. Ethyl cinnamate (Ethyl3-phenylpropenoate) 2. Propyl cinnamate (n-propyl 3-phenylpropenoate) 3. Isopropyl cinnamate (isopropyl 3-phenylpropenoate) 4.1-butyl cinnamate 5.2-butyl cinnamate 6. Methyl 2', 3'-dimethoxy- cinnamate 7. Methyl 2', 4'-dimethoxy- cinnamate 8. Methyl 3', 4'-dimethoxy- cinnamate 9. Methyl 3', 5'-dimethoxy- cinnamate 10. Methyl 3-phenylpropanoate 11. Methyl 3- (4'-methoxy- phenyl) propanoate 12. Methyl 3- (4'-hydroxy-3'- methoxyphenyl) propanoate

13. Methyl a-methyl-3-phenyl- propanoate (Methyl 2-methyl-3- phenylpropanoate) 14. Methyl oc"ß-dibromo-3-phenyl- propanoate (Methyl 2,3-dibromo- 3-phenylpropanoate) 15. Ethyl a, ß-dibromo-3-phenyl- propanoate (Ethyl 2,3-dibromo- 3-phenylpropanoate) 16. Methyl 3- (2'-methoxy- phenyl) propanoate 17. Methyl 3- (3'-methoxy- phenyl) propanoate 18. Isopropyl 3- (4'-methoxy- phenyl) propanoate

19. Methyl 3- (3'-bromo-4'- methoxyphenyl) propanoate 20. Ethyl 3-hydroxy-3- (2'- bromophenyl) propanoate 21. Methyl 3- (4'- (l-butoxy)- phenyl) propanoate

Compound No. 1 could be purchased from Aldrich, Sigma-Aldrich Sweden AB, Sol- kraftsvägen 14C, 135 70 Stockholm with catalogue No. 11,237-2. Compound No. 10 could be purchased from Lancaster, Lancaster Synthesis Ltd., Newgate, White Lund, Morecambe, Lancashire LA3 3DY, UK with catalogue No. 5310. In Table 1 is given CAS numbers for compounds No. 2-9,11-17, and 19-21. CAS numbers marked with an asterisk (*) are those preferred by Beilstein. Compound No. 18 could be prepared as follows: Isopropyl 3- (4'-hydroxyphenyl) propanoate (Registry Number: 116144-68-4) was re- acted with methyl iodide in acetone/potassium carbonate to give isopropyl 3- (4'- methoxyphenyl) propanoate (Compound No. 18). The product was verified with NMR.

'H NMR 5 1. 21 (6H, d, J =6. 4 Hz), 2.55 (2H, t, J = 7. 8 Hz), 2.88 (2H, t, J = 7. 8 Hz), 3.78 (3H, s), 5.00 (1H, sept, J = 6.4 Hz), 6.82 (2H, d, J = 8. 7 Hz) and 7.12 (2H, d, J = 8.7 Hz).

Table 1. CAS numbers for compounds No. 2-9,11-17, and 19-21. Compound No. CAS numbers 2 7778-83-8, 74513-54-5,74513-58-9 3 7780-06-5*, 28514-01-7,60512-85-8 4 538-65-8*, 52392-64-0, 52392-65-1 5 7726-62-7*, 17377-82-1 6 15854-60-1 7 66417-42-3*, 15854-55-4,84385-10-4 5396-64-5*, 30461-77-9,30461-78-0 9 29589-65-4*, 76104-60-4 Yl15823-04-8 12 5602-44-3 13 29393-16-6, 29417-83-2, 38574-62-8, 78964-60-0 14 21770-48-9, 52742-03-7,52777-73-8,113569-01-0,113626-43-0 15 5467-70-0*, 30983-70-1, 87439-83-6, 99107-37-6,99570-22-6, 99570-23-7,100227-07-4 16 55001-09-7 17 50704-4 19 288310-70-3 20 70200-15-6 21 115514-10-8 By the expression"comprising"we understand including but not limited to. Thus, other non-mentioned substances, additives or carriers may be present.

The invention will be illuminated by the following Examples, which are only intended to illuminate and not restrict the invention in any way.

Examples Experimental Insects. The insects used for the experiments was the pine weevil (Hylobius abietis) taken from their natural environment, i e coniferous forests.

Preparation of gnawing-inhibiting compositions. The compositions are prepared by incorporating the compounds in a suitable matrix. When the compounds are not solu- ble in the matrix a solvent is used to transfer the compounds into the matrix. A 50 mM solution in methyl acetate was applied on the pine bark, except for compound No. 12, wherein a 50 mM solution in methanol were used. For compound No. 11, both solu- tions were used.

Example 1-Test of gnawing-inhibiting effect of substances applied on pine bark.

For each test, 40 pine weevils (20 females + 20 males) were used placed in separate Petri dishes provided with a piece of a pine twig enveloped in aluminium foil. In the foil, two holes with a diameter of 5 mm were punched, whereby the underlying bark was exposed. One of the two surfaces exposed was treated with 100 ; n, l of a 50 mM solution of the substance that was tested, and the other surface was treated with the same amount of solvent alone (control). After 6 and 24 hours, respectively, it was re- corded whether the pine weevil had started to eat on the treated and untreated surface, respectively. In Table 2 the gnawing-inhibiting effect is shown by means of the fol- lowing index: (C-T ! xlOO (C+T), wherein C is the number of control surfaces with gnawing and T is the number of treated surfaces with gnawing. It was tested if there was a statistic signifi- cant difference between treatment and control with a chi2-test of a 2x2 table (not con- tinuity corrected): *=p<0. 05, **=p<0. 01, ***=p<0. 001. Table 2. Test of gnawing-inhibiting effect of substances applied on pine bark (methyl acetate used as a solvent when nothing else is stated). Compound No. Index value after 6 hours Index value after 24 hours 100*** 67*** 2 73*** 64*** 3 83*** 79*** 4 79*** 43*** 5 70*** 44*** 6 100*** 85*** 7 92*** 76*** 8 41** 12 ns 9 58*** 26** 10 87*** 11 ns 11 94*** (methyl acetate) 76*** (methyl acetate) 100*** (methanol) 100*** (methanol) 12 68*** (methanol) 12 ns (methanol) 13 100*** 64*** 14 50** 25** 15 91*** 39*** 16 100*** 95*** 17 93*** 79*** 18 91*** 72*** 19 43 ns 35** 20 64*** 39*** 21 100*** 67*** Example 3-Field test with 80 saplings The antifeedant effect of ethyl 2,3-dibromo-3-phenylpropanoate (compound No. 15) applied on stems of Norway spruce seedlings was assessed in a field test. The active

substance was dissolved in methanol and to this solution a liquid wax (AGS 3512 Ul- tra, Trion Tensid AB, Uppsala, Sweden) was added in the proportion 3: 1 (metha- nol : AGS), giving 0,056 g of active substance per mL of the final mixture. About 2 mL of this mixture (containing 0.11 g of active substance) was applied on each seedling in a way that it completely covered the lower half of the stem. This treatment was com- pared with seedlings similarly treated with the same methanol/AGS mixture without the active substance and also with untreated seedlings. A randomise block design was used with each of the 80 blocks containing one seedling of each of the three treat- ments. The distance between seedlings within a block was about 0.5 m and the dis- tance between blocks about 2 m. The seedlings were planted on a fresh clear-cutting 13 km NNE Uppsala, Sweden, on 11 June 1999. The amount of pine weevil feeding was recorded for each seedling after 19 and 36 days.

The application of ethyl 2,3-dibromo-3-phenylpropanoate (compound No. 15) on spruce seedlings significantly reduced the amount of pine weevil feeding on the stems (Table 3). After 5 weeks the damage level was 4 times higher on control seedlings treated with methanol/AGS without the active substance and 3 times higher on un- treated seedlings. Thus, methanol/AGS alone tended to increase damage, but this ef- fect was counteracted when the active substance was added.

Table 3. Pine weevil feeding in the field on seedlings treated with ethyl 2,3-dibromo- 3-phenylpropanoate (compound No. 15) and on control seedlings of two different types. Column means followed by the same letter are not significantly different at the 5 % level (ANOVA (GLM Proc., SAS) of log-transformed data followed by Tukey's HSD test). Treatment of seedlings No. of attacked seedlings Mean (SE) debarked area (n=80) (cm2) per seedling (n=80) 19 days 36 days 19 days 36 days Compound No. 15 + 27 63 0. 62 (0.14) a 1.63 (0.22) a MeOH + AGS Control : MeOH + AGS 58 71 4. 66 (0.46) b 6.53 (0.41) b Control : Untreated 47 69 3. 28 (0.40) c 5.09 (0.38) b

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