THE INFESTATION OF EUROPEAN LARCH LARIX DECIDUA MILL. DWARF SHOOTS BY DASINEURA KELLNERI (HENSCHEL) (DIPTERA: CECIDOMYIIDAE) IN THE OJCOW NATIONAL PARK IN SOUTHERN POLAND

Małgorzata Skrzypczynska
Department of Forest Entomology, Agricultural University of Cracow, Poland

ABSTRACT

The results of the study concerning damage to dwarf shoots of Larix decidua Mill. caused by Dasineura kellneri (Henschel) have been presented. The study was conducted in 2005–2006 at three localities in the Ojców National Park in southern Poland. A total of 240 branches (each 1 m long) with 19 265 dwarf shoots, collected from 60 larches were designated to the study. The analysis showed that the percentage of dwarf shoots damaged by D. kellneri was 15.3 in 2005 and 25.0 in 2006.

The U Mann-Whithey test at the significance level of 0.05 was used in statistical analysis of the data.

Key words: Larix decidua, dwarf shoots, insect pest, Dasineura kellneri.

* Part of this investigation in sponsored under the reference DS-3424/L-KEnL/06.

INTRODUCTION AND AIM

Silvicultured and utilizable values of European larch Larix decidua Mill. resulted in considerable interest in this tree species in the present time. Among the primary physiological pests, Dasineura kellneri (Henschel) (Diptera, Cecidomyiidae) is frequently reported [3, 4, 6, 7, 8, 9, 10].

Its larvae damage the buds on larch dwarf shoots, and when numerous, they can cause the death of whole branches.

There are few data in the literature concerning damage to dwarf shoots caused by D. kellneri. For this reason, a study has been undertaken with the aim to determine the extent of damage to larch dwarf shoots caused by this insect during two consecutive years.

MATERIAL AND METHODS

Field studies were carried out in the Ojców National Park in July of 2005 and 2006. In each of the three localities investigated, i.e. Brama Krakowska, Złota Góra, and near Skała, 10 larch trees, 20–60 years of age, were selected at random. From the lower part of the crown of each tree four twigs, 1 m in length, were taken at random. Each year, 120 twigs with dwarf shoots were collected, i.e. 240 twigs were investigated in total. They were examined in laboratory. The damage (Fig. 1) was identified with help of works of authors: Buhr [1], Schnaider [5], Skuhravý and Skuhravá [10].

The statistical analysis of the data was used. The question was whether there is a significant difference between the number of dwarf shoots damaged by D. kellneri and the number of all dwarf shoots on the investigated twigs in three localities in 2005 and 2006.

Studies comprised fraction of dwarf shoots damaged by D. kellneri on twigs, and the fraction was assumed to be the number of damaged the dwarf shoots divided by the total number of dwarf shoots on the twigs. The U Mann-Whitney test at the significance level of 0.05 was used.

RESULTS AND DISCUSSION

There were 19 265 dwarf shoots, including 3 882 (20.1%) damaged ones, present on the 240 investigated twigs, collected in three localities over two consecutive years (Table 1-3). In 2005, the minimum and maximum numbers of damaged dwarf shoots were found in the case of localities: Brama Krakowska and Złota Góra, 1 (0.3%) and 115 (39.1%), respectively. A year later, the minimum was 6 (2.0%) found in the case of localities Brama Krakowska and Złota Góra, while the maximum was 285 (91.6%) in the locality near Skała (Tables 1, 2 and 3).

For individual localities the lowest mean number of damaged dwarf shoots, i.e. 40.0, was found in the case of the locality Złota Góra, in 2005, while the highest mean number, i.e. 131.6, for the locality near Skała, in 2006.

For all localities, mean numbers of damaged dwarf shoots in 2005 and 2006 were 489.7 and 804.3, respectively. The mean percentage of infested dwarf shoots in 2006 was about 1.6 times higher than in 2005 (25.0% and 15.3%, respectively).

The results of the statistical analysis (Table 4) showed that no unequivocal correlation was found (Fig. 2, 3) between the number of dwarf shoots damaged by Dasineura kellneri and the total number of ones on a twig of Larix decidua.

Occasionaly it may occurs e.g. in the locality near Skała (Fig. 4) as well as for all mentioned localities (Fig. 5).

Field investigations carried out in the Ojców National Park in former years has shown that the percentage of dwarf shoots damaged by D. kellneri was vary. In 1993 mentioned percentage was 1.8 [6], and in 2002–2003 D. kellneri destroyed 15.0% and 12.4%, respectively [7].

In the case of the larches in plantation at Kolanów (Forest District Brzesko, near Kraków), in 1973, the minimum and maximum percentage of damaged dwarf shoots were found, 4.4 and 20.9, respectively [2].

Undoubtedy, this phenomenon is affected by abiotical and biotical factors.

Investigations should be continued over several years in order to ascertain whether certain recurrent relationships are accidental.

CONCLUSIONS

1. The number of dwarf shoots of L. decidua damaged by Dasineura kellneri vary in different localities during consecutive years.

2. There was no unequivocal correlation between the number of dwarf shoots damaged by D. kellneri and the total number of dwarf shoots on a twig of L. decidua.

3. In general D. kellneri did not show the greater economic significance during the study period.

ACKNOWLEDGEMENTS

Grateful thanks to Prof. Dr. Tadeusz Kowalski for realized the photograph and to Dr. Lucylla Rutkowska for performing statistical calculations.

REFERENCES

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7. Skrzypczyńska M. 2004. Relationships between the number of dwarf shoots of Larix decidua Mill. damaged by different insect species in the Ojców National Park in southern Poland. Journal of Pest Science, 77, p. 173-177.

8. Skuhravá M., Skuhravý V. 1960. Bejlomorky. [Gall-midges]. ČSAZV, Praha [in Czech].

9. Skuhravá M., Skuhravý V., Brewer J.W. 1984. Biology of gall midges. In: Ananthakrishnan T.N. (ed.) Biology of gall insects. Oxford IBH, New Delhi, p. 169-222.

10. Skuhravý V., Skuhravá M. 1998. Bejlomorky lesnich stromů a keřů. [Gall midges of forest trees and shrubs]. Matice lesnicka, Pisek [in Czech].

Accepted for print: 17.01.2007

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