Petercord: Flight period of the broad-leaved Ambrosia L. in Luxembourg and Rhineland-Palatinate between 2002 and 2005

FLIGHT PERIOD OF THE BROAD-LEAVED AMBROSIA BEETLE TRYPODENDRON DOMESTICUM L. IN LUXEMBOURG AND RHINELAND-PALATINATE BETWEEN 2002 AND 2005.

Ralf Petercord

Forstliche Versuchs- und Forschungsanstalt Baden-Württemberg, Wonnhaldestraße 4, D-79100 Freiburg, Germany Abstract

The flight period of Trypodendron domesticum L. (Coleoptera, Scolytidae) was studied by exposing ethanol and pheromone baited traps in 32 beech stands in Luxembourg and Rhineland-Palatinate between 2002 and 2005. In each year under study the flight period shows three maximums for swarming activity in the middle/end of March, middle of April/beginning of May, and end of May/beginning of June. The first two maximums characterise the beginning of the flight period and its continuation following bad weather conditions. The third maximum of swarming cannot be explained by the present knowledge about the alteration of generations of Trypodendron domesticum L.. The possibility of a second generation is discussed.

Keywords: wood boring , Xyloterus domesticus, second generation, alteration of generations, flight activity

1. Introduction

Since the spring of 2001 the infestation of living beech (full foliaged, with intact cambium) by the wood boring, xylomycetophagous broad-leaved ambrosia beetle (Trypodendron (syn. Xyloterus) domesticum L.) is observed in Belgium, Luxembourg and Rhineland-Palatinate (Eisenbarth et al. 2001). This attack by T. domesticum, known as a secondary invader, is a fundamentally new type of damaged, which has not been observed so far. The successful infestation of vital beeches by ambrosia would be a serious danger for the forestry in Central European beech stands and the beech dominated ecological systems.

2. Materials and methods

Monitoring of the flight activity of Trypodendron domesticum was done in 32 differently strongly damaged beech stands in Luxembourg and Rhineland-Palatinate (Fig. 1) in the period 2002 until 2005. Five pheromone-baited traps (denat. Ethanol/ Lineatin) were set up in each beech stand. The five traps were arranged in form of a cross with an edge length of 100 m oriented at the main directions (N, E, S, W) and with one trap in the center (C) of the cross.

IUFRO Working Party 7.03.10 Proceedings of the Workshop 2006, Gmunden/Austria 213 Petercord: Flight period of the broad-leaved Ambrosia beetle Trypodendron domesticum L. in Luxembourg and Rhineland-Palatinate between 2002 and 2005

3. Objectives

a. Monitoring of the flight period and the population dynamics of the broad-leaved ambrosia beetle Trypodendron domesticum L. b. Estimation of the exposure of beech stands to a possible infestation of living trees. c. Development of preventive forest protection strategies to conserve beech forests.

Fig. 1: Geographical situation of the trap locations in the research area (Blue points). North and/or northwest the red line as well as red circled are regions with strong occurrence of the beech bark disease.

4. Results

The flight period of Trypodendron domesticum L. begins at an air temperature of 9.5° C depending on the weather conditions in early spring and extends into July. In 2004 beetle flight was observed in the first week of February already. However the flight activity was interrupted by a renewed beginning of winter lasting until the middle of March. At the beginning of each of the four capture periods exclusively Trypodendron domesticum have been caught. For each year the capture results clearly varies between the different forests stands. However a common trend for the three regions Luxembourg, western Hunsrück (district Trier- Saarburg) and the western Eifel (district Bitburg- Prüm) can be discovered (Fig. 2). After a distinct decline in the capture results from 2002 to 2003, there was a renewed increase in 2004. This was more distinct in the Hunsrück and in the Eifel than in Luxembourg. 2005 a decrease of the capture results has been observed in all three regions. Through all the years of research, the flight has been characterized by three peaks of the swarming activity (Fig. 3). The first peak occurred mid/end of March and indicates the beginning of the flight period. The second peak appeared from mid of April to beginning of May and was noticeably lower. The third peak was on a higher magnitude than the second one and has been observed regularly from end of May to beginning of June, approximately ten weeks after the first maximum.

IUFRO Working Party 7.03.10 Proceedings of the Workshop 2006, Gmunden/Austria 214 Petercord: Flight period of the broad-leaved Ambrosia beetle Trypodendron domesticum L. in Luxembourg and Rhineland-Palatinate between 2002 and 2005

Luxemburg (N = 17 (15)) Eifel (N = 7 (3)) 20000 17780 Hunsrück (N = 8 (9)) [N] 18000 15503 16000

14000 12386 12000 T. domesticum 10000 7568 8000 6504 6000 4459 3762 4000 2552 2725 23752307 2000 1194

average capture result 0 2002 2003 2004 2005 Observation year

Fig. 2: Average capture results of Trypodendron domesticum L. at the trap locations in Luxembourg, in the Hunsrück and in the Eifel in the observation years 2002 to 2005. (The capture results 2002 are only conditionally comparable, since in the Hunsrück and in the Eifel trap locations were given up an/or again arranged. In the legend the parenthese numbers indicate the numbers of trap locations in 2002).

IUFRO Working Party 7.03.10 Proceedings of the Workshop 2006, Gmunden/Austria 215 Petercord: Flight period of the broad-leaved Ambrosia beetle Trypodendron domesticum L. in Luxembourg and Rhineland-Palatinate between 2002 and 2005

4500

[N] 4000

3500

3000 LUX 2002

T. domesticum T. 2500 RLP 2002 LUX 2003 2000 RLP 2003 1500 LUX 2004 RLP 2004 1000 LUX 2005 500 RLP 2005 average capture result capture result average 0 28.02 14.03 29.03 11.04 25.04 09.05 23.05 06.06 20.06 Date of trap checking

Fig. 3: Process of the beetle flight of Trypodendron domesticum L. in Luxembourg and Rhineland-Palatinate (2002-2005).

The three peaks of swarming were observed at all trap locations, however within the four year period they appeared on different levels. Three groups of trap locations can be differentiated. One group is characterised by an early maximum of flight activity, 50% of the beetles flew before the end of March (Typ I). In another group the beetles flew disticntably later, only 50% had flown at the end of May (Typ III). In a third group of trap locations (Typ II) the proportions of beetles with an early maximum of flight activity and the ones with a late maximum of flight activity were equal (Fig. 4).

IUFRO Working Party 7.03.10 Proceedings of the Workshop 2006, Gmunden/Austria 216 Petercord: Flight period of the broad-leaved Ambrosia beetle Trypodendron domesticum L. in Luxembourg and Rhineland-Palatinate between 2002 and 2005

100 F1 90 F2 F3 80 F4 70 F5 F6 60 F7 50 50 % F8 F9 40 F10 F11 30 F12 20 F13 F14 10 I II III F16

Relative portionRelative capture result of total the [%] 0

.04 4.04 6.04 02.04 03.04 03 03.04 03.04 03.04 04.04 0 04.04 04.04 05.04 05.04 05.04 06.04 06.04 06.04 0 06.04 07.04 07.04 07.04 08.04 3. 25. 0 10. 17. 24. 31. 07. 14. 21. 28. 05. 12. 19.05.0426. 02. 09. 16. 23. 30. 07. 14. 21. 28.07.0405. Date of trap checking Fig. 4: Process of the beetle flight (2004) at the trap locations in Rhineland-Palatinate, represented as sum curves of the relative portion of the total capture result for each trap location.

5. Discussion and conclusion

The results of the monitoring prove that Trypodendron domesticum L. is qualified to perform a distinct population change just like bark-breeding beetles. In all three regions of the research area the separate populations changed within a year from retrogradation into a renewed progradation. For Central Europe Trypodendron domesticum L. is described in the literature as univoltine species (Schwenke 1974, Schwerdtfeger 1981). This assessment is based primarily on the assumption of an analogy to the biology of Oliv. (Schwerdtfeger, 1963). The progression of the flight activity of Trypodendron domesticum L. observed within the period 2002 to 2005, characterise by an unexpectedly high early summer maximum at the end of May/at the beginning of June, cannot be explained by the present knowledge about the alteration of generations of Trypodendtron domesticum L.. At several trap locations the proportion of beetles with a late maximum of flight activity was more than 50% of all captured beetles. This can not be explained by the existence of subsequent broods and/or the swarming of latecomers.The first two peaks characterise the beginning of the flight period and its continuation following bad weather conditions. The third swarming peak can not be explained with unfavourable weather conditions. In fact only two explanations are possible for the early summer maximum. The occurrence of a second generation or the occurrence of different swarming types (early and late beetle flight) within the population. The existence of a second generation has been demonstrated by a study of Eichhorn and Graf (1974). In a breeding image analysis of Trypodendron domesticum L. in 1968 in the Soonwald (Hunsrück) a second generation of beetles was found. An appropriate proof could not be demonstrated in the available study. Genetic investigations, which could prove the occurrence of different swarming types, are yet to be carried out.

IUFRO Working Party 7.03.10 Proceedings of the Workshop 2006, Gmunden/Austria 217 Petercord: Flight period of the broad-leaved Ambrosia beetle Trypodendron domesticum L. in Luxembourg and Rhineland-Palatinate between 2002 and 2005

6. References

EICHHORN, O., GRAF, P. (1974): Über einige Nutzholzborkenkäfer und ihre Feinde. – Anz. Schädlingskde. Pflanzen-Umweltschutz 47: 129 – 135.

EISENBARTH, E., WILHELM, G. J., BERENS, A. (2001): Buchen-Komplexkrankheit in der Eifel und den angrenzenden Regionen. – AFZ-DerWald 56 (23): 1212-1217.

SCHWENKE, W. (1974): Die Forstschädlinge Europas. 2. Band Käfer – Paul Paray, Hamburg, Berlin. 500 pp.

SCHWERDTFEGER, F. (1963): Zur Generationsfrage beim Gestreiften Nutzholzborkenkäfer – Forst- und Holzwirt 18: 449-451.

SCHWERDTFEGER, F. (1981): Die Waldkrankheiten. 4. Aufl. – Paul Paray, Hamburg, Berlin. 486 pp.

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