Techn cal field

The present invention relates to a method for combating the eight toothed spruce bark beetle, Ips typographus, as well as the closely related species, Ips acu natus and Ips sexdenta- tus, as well as a composition hereto.

The object of the present invention is to obtain a possibi lity to inhibit infestation of the eight toothed spruce bark beetle as well as closely related species.

A further object is to obtain a compos tion hereto.

Background of the invention

The interest for biological methods for inhibiting pest insects has steadi ly increased during the last decade. This i s particu¬ larly due for pheromones, the specie specific signal substances whi ch 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 biologi cally ac¬ tive in very small amounts to the target organi sm, often nano- gram amounts, and 3) the insects have great difficulty in deve¬ loping resistance against these natural signal compounds.

The high specie specifi city of the pheromones means that phero¬ mone 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 wi ll quite easi ly 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. Thi s i s natural as the pheromones as behaviour signal shall be short living. They are thus not accumulated in higher organi sms 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¬ romone has been demonstrated.

For the reason given above pheromone based inhibiting methods against pest insects are particularly harmless to the envi ron- 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 ki lled trees, growth losses and numerous damages of e.g. blueing fungus.

The eight toothed spruce bark beetle, Ips typographus 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 dying trees, e.g. windfallen trees. The larvae live of the nutr tionally rich bast layer

(phloem) underneath the outer bark. A male that bores into that excretes a pheromone consisting of 2-methyl-3-buten-2-o I (MB) and _c_i_ ^s ~ ^verDeno • CcV ⁾ . The pheromone attracts females to the tree but also other males. The pheromone is well known and MB and cV are uti lized since long on a commercial scale as an att- ration agent in traps for catching the eight toothed spruce bar k beet le .

The amount of MB and cV excreted by an inbored male increases during the first days and reaches a maximum when he has gnawed out a mating chamber and ready to allow one or more females 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. Thi s means that when many spruce bark beetles attacks a tree then the attract¬ ing pheromone signal from the tree wi ll increase rapidly. More -bark beet les 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. The stop signal i s, however, not comp¬ letely investigated. One very important component of this is, however, verbenonme, which is mainly produced by fungi and other micro organisms which start to grow in the path system gnawed by the beetles. The male of the spruce bark beetle wi ll himself excrete two substances, ipsenol, and ipsdienol, in amounts that increase during the Later phases simultaneously with the decrease of the attraction agents. Ipsenol and ips- dienol seem however, to have a restricted effect as a stop sig- na L .

Usually, the eight toothed spruce bark beetle lives in low po¬ pulation densities. In thi s endemic phase it mates in wind fal- Len, broken or otherwise damaged trees, whi ch 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 ki ll also healthy spruces. Such outbursts can be given a great ex¬ tent, as now lately during the 1970ties when primari ly in Varm- land, Sweden and parts of Norway, spruce forests for 100s mi l- lion crowns were ki lled. 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 generat ion ^" of spruce bark beetles.

Besides the eight toothed spruce bark beetle, Ips typographus, the spruce is being attacked by the six toothed spruce bark beetle, Pi tyogenes cha lcographus . The two species show a very similar way of Living. The attraction agent of the male of the six toothed spruce bark beetle consists of 2-ethy 1-1 ,6-dioxas- pironane having the trivial name chalcogran in a combination with the methyl ester of 2,4-decadi eni c acid (MD). Both subs- tances are commercially utilized today as attraction agents. It is hereby referred to United States Patent US-A-4,205 ,084 when chalcograne is concerned, and to Swedish Patent Application No. SE-A-8600448-8 when methyl decadienoate is concerned. Of chal¬ cograne the 2S,5R-enantiomer is preferred, and of the methyl ester the 2E,4I isomer is preferred.

Description of the present invention

It has now surprisingly been shown possible to be able to pre¬ vent attraction to spruce by uti lizing an attracting pheromone component of a competing specie, optionally in combination with an inhibiting pheromone component of the eight toothed spruce bark beetle. By utilizing only one of two synergistic attrac¬ tion agents of the competing specie attraction of this latter s avoided.

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. It has now turned out that methyl decadi¬ enoate of attraction system of the six toothed spruce bark bee-

tie also wi ll function as a stop signal to the eight toothed spruce bark beetle. It has further turned out that a combina¬ tion of verbenone and methyl decadienoate is superior each of the two substances as a stop signal to the eight toothed spruce bark beetle.

The present invention wi ll now be described more in detail with reference to the following examples, however, without being re¬ stricted the reto .

The inhibiting effect of either of methyl ,4-decad i enoate and verbenone as well as a combination of methyl 2, -de cad i enoate and verbenone on the eight toothed spruce bark beetle against its attraction agent consisting of MB + cV was investigated in a laboratory test. In this test a laminar ai r flow with a speed of 2 m/s was created over a surface covered by fi lter paper. A capi llary containing the substances was placed upwind. The bark beetles were released 10 at a time 14 cm downwind from the ca¬ pi llary. Those walking and orienting within a circle having a radius of 1.5 cm out from the capillary are regarded to have responded positively on the attraction agent. The method is de¬ scribed more in detai l by Byers, J.A. and Wood, D, J. Chem. Ecol. 7, 9-18, (1981) .

The result of a test series carried out in accordance with the above described technique is shown in the attached figure. It is evident that the attraction of males of the specie Ips typo¬ graphus to MB + cV is inhibited by MD or verbenone or both in combination, whereby the combination gives a superior effect

-9 already at a release rate of 2.2 x 10 g/min, but preferably

—8 at a release rate of 2.2 x 10 g/min, or more.

Due to the way of living MD alone or in combination with verbe¬ none the same effect against Ips acuminatus and Ips sexdenta- tus, which both are bark borer beetles closely related to Ips typographus .

At the use of the combination above to this aim the combination of verbenone and methyl decadienoate verbenone is applied in an absorbent, such as silica, zeolites, or porous polymers, such as of polyethylene, po lycarbami de, or dextrose derivatives, or be dispersed in an emulsion of a cellulose derivative, such as CMC, hydroxymeth I cellulose, other starch glues or gum forming po lysacchari des , so that the compound is released with an even amount for a long t me. The absorbent is sprayed 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, sum¬ mer 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 Lien trees .

FIG. 1 Inhibition of the attraction of Ips typographus in a La- boratory test with increasing amounts of either of (-)- verbenone and 2E,4Z-methyl decadienoate as well as the combination of this two, together with a constantly re¬ leased amount of the attracting pheromone components cis-verbenol and methyIbuteno L , the latter two each be- ing released in an amount of 2.2 x 10 g/min. The re¬ sult of the response indicated with the same letter are not significantly differing from each other in a test series.