Über Hausbock Hylotrupes bajulus (L.), (Col., Cerambycidae), in Laubholz: Versuche mit Laubholzarten, Prüfung der Wirkung von Ligninstoffen und von Ginkgo biloba, Beobachtungen an Hesperophanes. [On House-longhorn Beetle Hylotrupes bajulus (L.), (Col., Cerambycidae) in hardwood: Investigations with several hardwood-species, tests on activity of lignin components and Ginkgo biloba, observations on Hesperophanes]
Hylotrupes bajulus-larvae feed and develop in softwoods, hardwood acts as a feeding poison. The reason for this is still little known. According to literature some observations contradict this established opinion and the question was raised, whether the colour-strain scutifer (= lividus) is able to live in hardwood. Testing ten European and tropical hardwood-species (following the DIN-EN test procedure 46) with recently hatched larvae of the normal strain and var. scutifer (F3), all larvae died within 4 weeks. Breeding and test results indicated a lethal-factor in the scutifer-strain, as postulated by BECKER (1977). Larvae of medium weight (50...160 mg) transfered into blocs of 9 hardwood-species died or were badly affected within 60 days. Only in Ilomba (Pycnanthus angolensis) 7 of 10 larvae survived, 3 were still in good condition. In combined hardwood-softwood blocs, larvae survived much better, feeding predominantly in the softwood. But they often gnawed through the hardwood and pupation and development into the beetle-stage occured there. Derivates of lignin were tested according to testprocedures DIN-EN 46 (preventive activity) and DIN-EN 47 (determination of thresholds). None of the substances were active in nominal value within the range of concentrations (2.5 or 4%, 18 to 27 kg/m³) tested. The syringa-group, typical for hardwood-lignin, tested by Syringaacid, Syringaaldehyd and Acetosyringon, had no special effect. Wood of the Maiden hair-Tree, Ginkgo biloba (which shows negative reaction to Mäule-reagent by lack of the syringa-group like softwood) was very poisonious even after extractions by water and solvents to the larvae. Thus the softwood-indicator Hylotrupes bajulus underlines the more independent systematic position of the Ginkgobsida. The syringa-group seems not to be decisive alone. Observations of Hylotrupes in hardwood were reported mainly from South- and Southwest-Europe. New observations and breedings of single larvae revealed the probability, that this findings depend on Hesperophanes-species. For example the larvae of Hylotrupes and Hesperophanes cinereus are difficult to distinguish.