Herbivory on the pedunculate oak along an urbanization gradient in Europe : Effects of impervious surface, local tree cover, and insect feeding guild

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.Peer reviewe

Search for top-down and bottom-up drivers of latitudinal trends in insect herbivory in oak trees in Europe

The 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

The bigger the tree the better the seed – effect of Sessile oak tree diameter on acorn size, insect predation, and germination

Sessile oak is one of the ecologically and economically most important tree species in Europe. Recently, the importance of this species has been particularly highlighted in the context of climate change, where it is expected that these species will play a significant role within their natural range and beyond. To regenerate and expand the range of the sessile oak forests, a large amount of healthy acorns is needed. The acorn production and the acorns themselves are endangered by a large number of abiotic and biotic factors. As oak trees of different sizes do not produce the same amount of seed of the same quality, we investigated how the sessile oak tree diameter affects the acorn size, insect infestation, and germination rate. On the other side, as the acorn size influences the attack rates of the most significant acorn pest – Curculio glandium (Marsham, 1802), and the germination rates of both the damaged and healthy acorns we also investigated how the acorn dimensions influence the insect damage and germination rates, and how the insect damage influences the germination rates. We determined that the oak tree size influences some oak seed characteristics that are important for forest regeneration, while it does not affect others. A greater acorn yield was recorded on the bigger oak trees. The tree dimensions also had a significant influence on the acorn size. Greater average length, as well as greater average acorn diameter, were recorded on bigger trees. Although the tree size affects the acorn size, it does not influence the acorn insect predation rates or its germination rates. These parameters are affected by the acorn size itself. Bigger acorns had a greater germination rate. Insects preferred smaller acorns and had a significantly negative influence on the germination rate

Impact of regeneration by shelterwood cutting on the pedunculate oak (Quercus robur) leaf mining insect community

The regeneration of pedunculate oak by shelterwood cutting causes profound ecological changes in the regenerated stands. In this paper, we studied how the pedunculate oak leaf miner community changes after shelterwood cutting with a short regeneration period and does the stand age influence the trend of seasonal variation in their diversity. Leaf miners were chosen because they are a very diverse group of insects closely tied to their host plant. For this reason, their community reacts to all changes to which their host plant is subjected. Three regenerated (5, 10, and 15-year-old) and one control (110-year-old forest) stand were selected in the studied area. A total of 28 species of leaf miners were recorded in them. Many rare species disappeared after shelterwood cutting, while frequent and abundant species experienced a decline in numbers. That led to a decrease in diversity, which was the lowest in the 5-year-old stand. The diversity of leaf miners began to increase in the older regenerated stands. The highest diversity was observed in the control stand. A period of 5 years is needed for the recolonization of approx. 40% of the leaf miner fauna, while 10 years is the recolonization period for approx. 60% and 15 years for approx. 85% of the above fauna. The trend of seasonal variation of the diversity of the pedunculate oak leaf miner community varied in stands of different ages. The diversity of oak leaf miners was the lowest in spring, whereas it increased until the middle of summer and then decreased in all the studied stands

PRELIMINARY NOTES ON PUPAL PARASITISM RATES OF THE HORSE CHESTNUT LEAFMINER, CAMERARIA OHRIDELLA (LEPIDOPTERA: GRACILLARIIDAE) IN BELGRADE AND ISTANBUL

The aim of our study was to simultaneously determine the parasitism rates of C. ohridella pupae in Istanbul and in Belgrade. Collection of the pupae in Istanbul was carried out on three occasions, 12th of June, 3rd of July, and 1st of August, respectively, corresponding with the three generations of the leafminer per year. In Belgrade, samples were collected only during the spring generation of the leafminer, in the period from 7th to 11th of June, 2017. Severe drought stress of horse chestnut trees impaired development of the 2nd and the 3rd leafminer generation and made it impossible to collect reasonable numbers of Cameraria pupae after the first collection date. At each collection date, 150 pupae per location were taken and treated as independent factors and their influence on the parasitism rates of the C. ohridella pupae was examined using the two-way ANOVA. The parasitism rates of the C. ohridella pupae in Istanbul ranged from 16 to 28% at the 1st collection date, from 18 to 20% in the 2nd collection date, and from 4 to 8% in the 3rd collection date. Parasitism rates in C. ohridella pupae collected in Belgrade ranged from 0 to 12%. The majority of them (80%), however, were parasitized to a low level of 0 to 4%, only

Herbivory on the pedunculate oak along an urbanization gradient in Europe: Effects of impervious surface, local tree cover, and insect feeding guild

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.ISSN:2045-775