About the unique scent of oak-gall wasp infected leaves

What is it about?

An enormous diversity of gall wasp species can parasitize oak leaves, but the physiological implications of different gall wasp infections are poorly understood. We analysed the effects of infections by four different gall wasp species (Neuroterus anthracinus, N. albipes, Cynips divisa and C. quercusfolii) on foliage photosynthetic characteristics and volatile emission rates in Quercus robur that grow in Tartu Tammik planted by important people that have resided in or visited Tartu. Our work indicated that gall wasp infection resulted in major reductions in foliage photosynthesis rates and elicitation of emissions of green leaf volatiles, mono- and sesquiterpenes and benzenoids in infection severity-dependent manner. Different gall infections resulted in unique emission blends, highlighting a surprisingly selective host volatile response to various gall wasps.

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Why is it important?

As a dominant and popular tree species in Estonia and Northern Europe, the leaves of pedunculate oak (Quercus robur) trees are readily parasitized by an enormous diversity of gall wasp species. Infection by gall wasps leads to the formation of peculiar outgrowths – galls – on the leaf surface. The wasp galls are highly variable in size and shape, and can comprise a large fraction of leaf mass, but despite the fascinating appearance and frequency of their occurrence, the physiological implications of different gall wasp infections had been poorly studied. The results in this paper collectively provide valuable information for diagnosing oak infections using ambient air volatile fingerprints and for predicting the impacts of infections on photosynthetic productivity and whole tree performance.