Untersuchungen zu den Befallsbedingungen, zum Befallsablauf und zur Abwehr des Befalls von Laub- und Nadelholz durch den Sägehörnigen Werftkäfer (Hylecoetus dermestoides Latr. [Coleoptera, Lymexylidae])

Freiburg im Breisgau

2005

111 S.

46 Abb., 27 Lit. Ang.

Bandaufführung

127499

The Sawhorned Boring Beetle or Large Timber Worm (Hylecoetus dermestoides Latr.) is considered a secondary Pest, attacking sapwood, timber, felled logs or predominantly root stumps. Breeding is favourable occurring in beech and oak wood, but the larvae can also be encountered in all native conifers and hardwood species as well. Successful development of the larvae is crucially depending on suitable humidity conditions within the wood (30% to 120%). The nourishing fungal mycelium of the inoculated specific ambrosia fungus, (Endomyces hylecoeti Neger) expands on the walls of the larval galleries only in this environment. The exceptionally short living (2-4 days) adult beetles swarm on warm days (at about 20°c) from the End of March roughly up to the first or second week in June, according to weather conditions. Within their lift span, male beetles are devoted to finding their mates and females are tirelessly busy identifying suitable breeding material and depositing egg barches in wood crevices and rough bark. In Central Europe a lifecycle lasts as long as one to three days. Due to lacking mandibles the beetles do not cause any form of damage. In contrast, serious damage is caused by tunnelling of the larvae when colonising freshly felled logs. Initially, the fungal spores of Endomyces hylecoeti are passed on by the female beetles and cover the eggshells. As soon as the small larvae bore into the wood they introduce the fungus to their galleries. Henceforth they feed on the fungal mycelium exclusively. With their large chitin teeth at the tails end, they clear their galleries from boring dust to preserve the gallery climate for maximum fungus growth. Apart from huge amounts of emerging white boring dust which mainly show in July/August on shaded outer zones of infested trunks or stumps, clustered boreholes of different size are visible in the wood. Compared to infestation with other known Ambrosia beetles, there is no black discolouring surrounding the boreholes. On the inner side of stripped bark one may encounter bore dust coronas which serve to prevent loss of humidity. First, larvae might engrave wood oblique to annual rings, before tunnelling can reach the heartwood of even very thick trunks. Galleries may extend as far as 26 cm.