METHOD FOR INHIBITING SPRUCE BARK BEETLES

Abstract: The present invention relates to a method for inhibiting the six toothed spruce bark beetle Pityogenes chalcographus, by preventing aggregation and/or infestation of spruce, whereby one applies an inhibitory active amount of verbenone on spruce.

Description: METHOD FOR INHIBITING SPRUCE BARK BEETLES. DESCRIPTION Techni ca L field The present invention relates to a method for inhibiting the six toothed spruce bark beetle, Pityogenes cha Icog rapjnjs . The object of the present invention is to obtain a possibi lity to inhibit infestation of the six toothed spruce bark beetle. Background of the invention The interest for biological methods for inhibiting pest insects has steadily increased during the last decade. This is particu¬ larly due for pheromones, the specie specific signal substances which some animals, and then in particular insects, communica- te with, inter alia to find a partner prior to mating. Pheromo- ne based inhibiting methods against pest insects are characte¬ rized in that 1) they are highly specie specific, 2) the chemi¬ cal compounds used are relatively simple, and biologically ac¬ tive in very small amounts to the target organism, often nano- gram amounts, and 3) the insects have great difficulty in deve¬ loping resistance against these natural signal compounds. The high specie specificity of the pheromones means that phero- one based inhibiting agents are directed almost only against individuals of one single specie. Sometimes, furthermore, against closely related species. The chemical composition of the pheromones is as a rule of such a type that they will quite easily decompose by UV-light and micro organisms after an app¬ lication. Then they are decomposed to compounds which are com- pletely harmless to other organisms. This is natural as the pheromones as behaviour signal shall be short living. They are thus not accumulated in higher organisms in a nutritional chain. The development of resistance in the insects against specie specific pheromones is extremely improbable. In spite of a considerable use of pheromones in the inhibition of e.g. a cotton fly in California for a whole decade, no resistance has developed. No change whatsoever in the composition of the phe- ro one has been demonstrated. For the reason given above pheromone based inhibiting methods against pest insects are particularly harmless to the environ- ment. Furthermore, they have proved to be extremely efficient. Inhibition of forest damaging insects is an area where phero¬ mone based ' inhibiting methods already are of great importance as great economical values are at stake hereby. These is parti- cularly due for bark beetles which every years cause great los¬ ses both in form of killed trees, growth losses and numerous damages of e.g. blueing fungus. The six toothed spruce bark beetle. Pi tyogenes chacographus is one of the most serious forest pest insects in Europe. It can under certain circumstances attack and ki ll standing healthy spruces to a great extent. The specie normally mates in healthy as well as in dying trees, e.g. wind fallen trees. The larvae live of the nutritionally rich bast layer (phloem) underneath the outer bark. A male that bores into that excretes a pheromone consisting of 2-ethyl-1,6- dioxaspi ro- | 4,4 I -nonane, having the trivial name chalcogran (CH) and methyl-2,4-decad enoate (MD) . Both substances are used commercially today as attractants. In the case of chalcogran it is referred to the US Patent US-A-4,205,084, and in the case of methyl decadienoate it is referred to the Swedish Patent Appli¬ cation SE-A-8600448-8. Of chalcogran the 2S,5R-enantio er is preferred, and of methyl ester the 2E,4Z isomer is preferred. The pheromone attracts females to the tree but also other ma¬ les. The pheromone is well known and is uti lized since long on a commercial scale as an attraction agent in traps for catching the six toothed spruce bark beetle. The amount of pheromone excreted by an inbored male increases during the first days and thereby further males and females of the specie are attracted. By attracting further males he will obtain help in breaking down the defence system of the tree present in the form of a rich resin gum flow. The male wi ll then gnaw out a mating chamber and is ready to allow one or mo¬ re females therein, which after mating wi ll start laying eggs therein. The amount of pheromone attraction agent then deceases in order to be down at a very low level about one week after the male has started his boring into the bark. This means that when many spruce bark beetles attacks a tree then the attract¬ ing pheromone signal from the tree wi ll ϊn crease rapidly. More bark beetles wi ll be attracted and the number increases expo¬ nentially. Such a massive attack on a certain tree is characte¬ ristic for the reproduction strategy of the bark beetles. Cer¬ tainly, it is, however, devastating if too many bark beetles are attracted to the same tree. The competition for the limited feed for the larvae wi ll then become so great that many of them die. Thus the bark beetles excrete a stop signal for further attraction to that tree. Usually, the six toothed spruce bark beetle lives in low po- pulation densities. In this endemic phase it mates in wind fal¬ len, broken or otherwise damaged trees, which show a low vita¬ lity. Severe autumn storms with much of wind fallen spruce fo¬ rest offers, however, an excess of mating trees to the spruce bark beetle. The population thereof increases rapidly, and in particular if two such years follow on each other the spruce bark beetle can reach an epidemic phase in which the population density is so high that it, with success, .can attack and k"ι 11 also healthy spruces. Cut, unbarked spruce, which i's left in the forest during the swarming of the spruce bark beetle in May to June is, from the insects point of view, a perfect mating place. In order to prevent the bui lding up of epidemic popula¬ tion densities then pi les of cut spruce have be protected in some way. Today this is made in Sweden through legislation re¬ quiring cut spruce to be transported out of the forest before August 1, i .e., prior to the hatching of the new generation of spruce bark beetles. Description of the present invention It has now surprisingly been shown possible to be able to pre¬ vent attraction and thereby attach on spruce by uti lizing an inhibitor or stop signal compound of the pheromone related att- raction by applying an inhibiting amount of (+) and/or (-)-ver¬ benone, suitably in combination with an inert carrier. The eight toothed and six toothed spruce bark beetles compete which one another for the spruce as a mating place. It is, as mentioned above, known through previous work, that verbenone is a stop signal of the eight toothed spruce bark beetle, whereby verbenone prevents attraction of further spruce bark beetles to its attracting agent. The present invention wi ll now be described more in detail th reference to the following examples, however, without being re¬ stri cted the reto . Examp le The inhibiting effect of verbenone on the eight toothed spruce bark beetle against its attraction agent consisting of CH and MD was investigated in a field test. Hereby two glue traps were placed 1.7 m above the ends of a beam being 6 m long, which beam was rotated with a speed of 1 rpm/26 min. The traps con- sisted of a net cylinder having a diameter of 30 cm and having a height of 30 cm and manufactured of a net having a mesh size of 0.5 mm and being coated with Sticklem Special. The slow ro¬ tation of the pair of traps is intended to reduce the position caused variation of the trap catches which is common in field tests. In a control test the two traps released the same amount dose of E,Z-methyl decadienoate (18 .ug/24 hrs) and chalcogran (1 mg/24 hrs) which is the aggregation pheromone of Pi tyogenes cha lcographus . The catch did not significantly differ between the two traps. One trap caught 400 females and the other 422 females. Of the males 139, and 160 respectively, were caught. At a completely similar distribution 411 females were caught in each trap, which using the X -test is not significantly diffe¬ rent from 400/422 (p=0.59) . The corresponding value for the males is p=0.39. When the same test was repeated using the same attractants but with one of the traps furthermore provided with a verbenone dispenser releasing 9 x 10 g per minute the catches were nificantly reduced as evident from the Table 1 below. TABLE 1 Verbenone (Vn) as inhibitor of the attraction of the six toothed spruce bark beetle, Pi tyogenes chalcographus to its ag • gregation pheromone, methyl decadienoate (MD) and chalcogran (CH) . Sex Trap 1 Trap 2 X -test MD + CH MD + CH Females 400 422 p = 0.59 Males 139 160 p = 0.39 MD + CH MD + CH + Vn Females 409 174 p = <0.001 Males 165 100 p = <0.001 In the test above 9.1 x 10 g of verbenone were administered per minute. The active amount of verbenone can, however, be —9 —8 from 2.5 x 10 g/min, preferably from 2.5 x 10 g/min and in particular from 2.5 x 10 to 2.5 x 10 g/min. At the use of verbenone for this purpose, verbenone is applied in an absorbent, such as silica, zeolites, or porous polymers, such as of polyethylene, po lycarbami de, or dextrose deriva- tives, or is dispersed in an emulsion of a cellulose deriva¬ tive, such as CMC, hydroxymethyI cellulose, other starch glues or gum forming po lysacchar ides, so that the compound is releas¬ ed with an even amount for a long time. The absorbent is spray- ed over the store of wood in the forest. As the wood- does not become attacked the transport out of the forest can be spread during a longer time period and can be made during the autumn. In the same way, summer cutting can take place which means a more rational handling within forestry. The present invention can be used on standing spruce, but also, of course, on, and preferably on, cut spruce wood as well as fa I len t rees .

Claims: C LA IMS . 1. Method for inhibiting the six toothed spruce bark beetle Pi tyogenes chalcographus, by preventing aggregation and/or in¬ festation of spruce, characterized in that one applies an in- hibitory active amount of (+) and/or (-)- verbenone on spruce. 2. Method according to claim 1, characterized in that one adds so much of verbenone that one obtains a release of at least about 9 x 10 g of verbenone per minute 3. Method according to claim 2, characterized in that one adds so much of verbenone that one obtains a release of at least about 9 x 10 g of verbenone per minute.

Inventors: BYERS JOHN, LOEFQUIST JAN, BYERS, JOHN, LOEFQUIST, JAN
Applicants: BYERS JOHN, LOEFQUIST JAN, BYERS, JOHN, LOEFQUIST, JAN
Application year: 1990
Main classification: A01N31
IPC codes: A01N31, A01N35