AimThe strength of species interactions is traditionally expected to become stronger toward the Equator. However, recent studies have reported opposite or inconsistent latitudinal trends in the bottom-up (plant quality) and top-down (natural enemies) forces driving insect herbivory, possibly because these forces have rarely been studied concomitantly. This makes previous attempts to understand the effect of large scale climatic gradients on insect herbivory unsuccessful. Location Europe Time period 2018-2019Major taxa studied Quercus robur MethodsWe used scholar-based citizen science to simultaneously test for latitudinal variation in plantherbivore-natural enemy interactions. We further investigated the underlying climatic factors associated with variation in herbivory, leaf chemistry and attack rates in Quercus robur across its complete latitudinal range in Europe. We quantified insect herbivory and the occurrence of specialist herbivores as well as leaf chemistry and bird attack rates on dummy caterpillars on 261 oak trees. ResultsClimatic factors rather than latitude per se were the best predictors of the large-scale (geographical) variation in the incidence of gall-inducers and leaf-miners as well as of leaf nutritional quality. However, insect herbivory, plant chemical defences (leaf phenolics) and bird attack rates were not influenced by latitude or climatic factors. The incidence of leaf-miners increased with increasing concentrations of hydrolysable tannins and decreased with those of condensed tannins, whereas the incidence of gall-inducers increased with increasing leaf soluble sugar concentration and decreased with increasing leaf C:N ratios. However, neither other traits nor bird attack rates varied with insect herbivory. Main conclusionsThese findings help to refine our understanding of the bottom-up and top-down mechanisms driving geographical variation in plant-herbivore interactions, and urge for further examination of the drivers of insect herbivory on trees.

Aim The strength of species interactions is traditionally expected to increase toward the Equator. However, recent studies have reported opposite or inconsistent latitudinal trends in the bottom‐up (plant quality) and top‐down (natural enemies) forces driving herbivory. In addition, these forces have rarely been studied together thus limiting previous attempts to understand the effect of large‐scale climatic gradients on herbivory. Location Europe. Time period 2018–2019. Major taxa studied Quercus robur. Methods We simultaneously tested for latitudinal variation in plant–herbivore–natural enemy interactions. We further investigated the underlying climatic factors associated with variation in herbivory, leaf chemistry and attack rates in Quercus robur across its complete latitudinal range in Europe. We quantified insect leaf damage and the incidence of specialist herbivores as well as leaf chemistry and bird attack rates on dummy caterpillars on 261 oak trees. Results Climatic factors rather than latitude per se were the best predictors of the large‐scale (geographical) variation in the incidence of gall‐inducers and leaf‐miners as well as in leaf nutritional content. However, leaf damage, plant chemical defences (leaf phenolics) and bird attack rates were not influenced by climatic factors or latitude. The incidence of leaf‐miners increased with increasing concentrations of hydrolysable tannins, whereas the incidence of gall‐inducers increased with increasing leaf soluble sugar concentration and decreased with increasing leaf C : N ratios and lignins. However, leaf traits and bird attack rates did not vary with leaf damage. Main conclusions These findings help to refine our understanding of the bottom‐up and top‐down mechanisms driving geographical variation in plant–herbivore interactions, and indicate the need for further examination of the drivers of herbivory on trees.

Abstract. Scolytids constitute an insect group of forest ecosystems that is very important both ecologically and economically, and which has been well studied in most European countries. However, new species are found quite often, especially in regions searched less intensively to date. In this paper three species of scolytid fauna not previously known in Romania are reported for the first time: Trypodendron laeve, Xylosandrus germanus and Hylastes linearis. Individuals of all three species were collected in the north-eastern part of Romania. T. laeve was found only in natural coniferous forests, at altitudes above 1230 m and in association with T. lineatum, but in much lower abundance. The Asian species X. germanus was found in an old beech forest situated at a much higher altitude (760-900 m) than observed in western and central Europe. The third species, H. linearis, was captured as a single specimen in a plateau region (375 m).

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Scientific knowledge in the field of ecology is increasingly enriched by data acquired by the general public participating in citizen science (CS) programs. Yet, doubts remain about the reliability of such data, in particular when acquired by schoolchildren. We built upon an ongoing CS program, Oak Bodyguards, to assess the ability of schoolchildren to accurately estimate the strength of biotic interactions in terrestrial ecosystems. We used standardized protocols to estimate attack rates on artificial caterpillars and insect herbivory on oak leaves. We compared estimates made by schoolchildren with estimates made by professional scientists who had been trained in predation and herbivory assessments (henceforth, trained scientists), and trained scientists' estimates with those made by professional scientists with or without expertise (untrained) in predation or herbivory assessment. Compared with trained scientists, both schoolchildren and untrained professional scientists overestimated attack rates, but assessments made by the latter were more consistent. Schoolchildren tended to overestimate insect herbivory, as did untrained professional scientists. Raw data acquired by schoolchildren participating in CS programs therefore require several quality checks by trained professional scientists before being used. However, such data are of no less value than data collected by untrained professional scientists. CS with schoolchildren can be a valuable tool for carrying out ecological research, provided that the data itself is acquired by professional scientists from material collected by citizens.

Scientific knowledge in the field of ecology is increasingly enriched by data acquired by the general public participating in citizen science (CS) programs. Yet, doubts remain about the reliability of such data, in particular when acquired by school children. We built upon an ongoing CS program -Oak bodyguards -to assess the ability of European schoolchildren to accurately estimate the strength of biotic interactions in terrestrial ecosystems. We used standardized protocols to estimate predation rates on artificial caterpillars and insect herbivory on oak leaves and compared estimates made by school children, trained and untrained professional scientists (with no or limited expertise in predation or herbivory assessment). Compared to trained scientists, both schoolchildren and untrained professional scientists overestimated predation rates, but assessments made by the latter were more consistent. School children overestimated insect herbivory, as did untrained professional scientists. Thus, raw data acquired by school children participating in CS programs cannot be used and require several quality checks. However, such data are of no less value than data collected by untrained professional scientists and can be calibrated for bias.

The native range of each species, the first report and the present distribution in Europe and in Romania are discussed. The new records suggest that all the analysed species have established populations in our country and a more widespread distribution than that previously known. Some of them attain sometimes locally or zonally high population levels and are regarded as important pests. For the most species, new observations are necessary, both concerning their presence in the areas where they were not found so far, but also to assess the impact of insect populations on their hosts and on the recipient biocoenoses. A particular attention should be paid to the species H. axyridis, whose swarms invade the houses of the people during the autumn and could cause annoyance and possibly allergy. Citizen participation in observing and reporting of these new "guests" is encouraged.

Urbanization is an important driver of the diversity and abundance of tree‐associated insect herbivores, but its consequences for insect herbivory are poorly understood. A likely source of variability among studies is the insufficient consideration of intra‐urban variability in forest cover. With the help of citizen scientists, we investigated the independent and interactive effects of local canopy cover and percentage of impervious surface on insect herbivory in the pedunculate oak (Quercus robur L.) throughout most of its geographic range in Europe. We found that the damage caused by chewing insect herbivores as well as the incidence of leaf‐mining and gall‐inducing herbivores consistently decreased with increasing impervious surface around focal oaks. Herbivory by chewing herbivores increased with increasing forest cover, regardless of impervious surface. In contrast, an increase in local canopy cover buffered the negative effect of impervious surface on leaf miners and strengthened its effect on gall inducers. These results show that—just like in non‐urban areas—plant–herbivore interactions in cities are structured by a complex set of interacting factors. This highlights that local habitat characteristics within cities have the potential to attenuate or modify the effect of impervious surfaces on biotic interactions.