Proceedings: Ecology, Survey and Management of Forest Insects GTR-NE-311 2750 Fig
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Trypodendron domesticum and Trypodendron signatum: Two Scolytid Species Involved in Beech Decline in Belgium B. Gaubicher1, M. De Proft1 and J.-C. Gregoire2,3 1Department of Phytopharmacy, Agricultural Research Center of Gembloux, Belgium 2Laboratoire de Biologie animale et cellulaire, Université Libre de Bruxelles, Belgium 3Fonds National Belge de la Recherche Scientifique, Bruxelles Introduction Xylophagous scolytids (Ambrosia beetles) have long been known to prefer fallen or seriously weakened trees and stumps. They are attracted to this host material by ethanol produced by the fermenting phloem and sapwood. However, these insects have begun aggressively attacking living beeches in Southern Belgium, raising the issue of a possible shift towards primarity. More than 1.3 million m³ have been attacked in 2001 (Huart and Rondeux 2001). Strikingly, similar occurrences of ambrosia beetles attacking living broadleaf trees have been observed worldwide recently. A series of experiments have been carried out since December 2000 to answer a series of rather basic but essential questions : what is the beetles’ phenology ? Do they have two generations a year ? What are the patterns of emergence for both species ? How far from an outbreak focus do they represent a threat to other stands? Material and Methods Phenology Four baited Theyson traps (distance between traps : 50 m) were placed in four attacked sites in the Ardennes. Catches were counted and identified once each week from the begining to the end of the flight period for both species. Patterns of Emergence 15 individual and 23 collective emergence traps were placed on infested trees at the end of the 2001 flight period. Catches were counted and identified once each week from 12 July to 3 October for individual traps, and from 1 August to 1 October for collective traps. Life Cycle and Parental Care In 2001, galleries of the two species were opened periodically during the attack period, from early April to the end of June, in order to observe the behaviour of adults inside, check on the development of progeny, and to determine whether or not a second generation exists. Dispersal of Trypodendron spp. from Beech Stands to Open Areas In Recogne and Witry, three and four baited (ethanol+lineatin) traps were placed in an open area at 50, 100 and 200 m, and at 50, 100, 200, and 400 m from the edge of an infested beech stand. Catches 180 160 were counted and identified once each week during 140 the flight period - from 2 April to 23 May, 2002 for 120 Anlier 100 Croix-scaille Recogne, and from 24 April to 23 May for Witry. 80 Gedinne 60 Libin Mean catches 40 Results 20 0 Phenology 2/5/2002 3/5/2002 4/2/2002 4/9/2002 5/7/2002 6/4/2002 7/2/2002 2/12/2002 2/19/2002 2/26/2002 3/12/2002 3/19/2002 3/26/2002 4/16/2002 4/23/2002 4/30/2002 5/14/2002 5/21/2002 5/28/2002 6/11/2002 6/18/2002 6/25/2002 The flight period for T. signatum was about one Date month later than for T. domesticum (Fig. 1 and Figure 1.—Phrenology of T. signatum. 134 Proceedings: Ecology, Survey and Management of Forest Insects GTR-NE-311 2750 Fig. 2). The earlier flight of T. domesticum might 2500 perhaps be connected to the fact that it 2250 2000 overwinters in the galleries where it might be able 1750 Anlier to feed throughout the winter on fungi. 1500 Croix-scaille 1250 Gedinne 1000 Libin Mean catches Mean 750 Patterns of Emergence 500 250 We observed that most young adults of T. 0 signatum emerged from their galleries at the end of the summer. They probably spent the winter in 05/02/02 04/03/02 11/03/02 18/03/02 28/03/02 04/04/02 11/04/02 26/04/02 07/05/02 15/05/02 24/05/02 07/06/02 20/06/02 27/06/02 08/07/02 the litter, at which time they were not attracted to Date pheromone traps. T. domesticum did not emerge Figure 2.—Phrenology of T. domesticum. from their galleries before spring. They overwintered in the galleries. Life Cycle and Parental Care For both species, parental care (essentially cleaning of the gallery by the female) is continuous until pupation is completed. We have observed one male at the entrance of each gallery. The exact role of the male during this period is still not clear; males may be guarding the female or may help to clean the gallery. Egg laying occurred in one single period, after which the larvae developed and pupated. There was thus no sister generation within any single gallery. Dispersal of Trypodendron spp. from Beech Stands to Open Areas The two Trypodendron species are obviously able to disperse beyond beech stands at least as far as 400 3000 meters (Fig. 3 and Fig. 4). This suggests that 2500 dispersal could occur between beech stands during 2000 outbreaks. Lines of baited traps placed at the edge of attacked stands might possibly prevent or reduce 1500 1000 these movements. Mean catches 500 Open Questions 0 T domesticum and T. signatum diverge in many 50 m 100 m 200 m respects, for example in their reproductive biologies, Distance from the beech stand edge (open field) modes of overwintering, spectra of host-trees, and Figure 3.—Dispersal of Trypodendron spp. in competitiveness. We need to conduct further studies recogne, Wallonia, Belguim (02/02/02 to 23/05/02). to help us understand how these species share their resources, to assess more accurately the risk that they represent, and to design appropriate control measures. 700 600 References Cited 500 Huart, O. and Rondeux, J. 2001. Genèse, évolution et 400 multiples facettes d’une maladie inhabituelle affectant ² le hêtre en région wallonne. Forêt wallonne 52 :9-19. 300 Mean catches Mean DNF. 2002. Maladie du hêtre wallon : évolution et 200 mesures. Paysages 22 :4-9. 100 0 50 m 100 m 200 m 400 m Distance from the beech stand edge (open field) Figure 4.—Distance from the beech stand edge (open field). Proceedings: Ecology, Survey and Management of Forest Insects GTR-NE-311 135.