The effect of root volatiles on the orientation behaviour of cockchafer larvae in the soil The present study investigates the effect of root volatiles on the orientation behaviour of cockchafer larvae Melolontha hippocastani in the soil. Cockchafer larvae are known as severe pests in agriculture and forestry. The present study adresses three relevant aspects of their chemical ecology linked to food choice belowground: Volatile organic compounds (VOCs) of several potential host plant roots and shoots are investigated and analysed by using gas chromatography mass spectrometry (GC MS). The obtained volatile patterns of damaged roots differ clearly from the undamaged ones. Emitted shoot volatiles differ clearly from the emitted root volatiles. Electrophysiological methods are employed to record sensory reactions of the detached larval antennae to several of the previously identified compounds. Volatile emissions of Quercus sp. are investigated in detail. By using electroantennography (EAG) changes in the receptor potential elicited by odour stimuli are recorded. It turns out that seasonal and maybe also circadian rhythms appear to play an important role in cockchafer larvae antenna physiology. The behavioural response of cockchafer larvae is tested on selected compounds. A dual choice test setup is designed to study the behavioural orientation of the belowground living larvae. Attractive and repellent compounds in host plants are identified. Preparative methods show the antennal lobes (ALs first central processing unit for olfactory information processing in the insect brain) of 3rd instar of M. hippocastani to contain a high number of glomeruli which are regarded as the functional subunits of odour discrimination ...