No abstract

SummaryUnderstanding the relationship between nitrogen (N) availability and stand health in forest ecosystems is crucial, because a large proportion of European forests is subjected to N-deposition levels beyond their retention capacity.We used data from a long-term forest monitoring programme (ICP Forests) to test the relationship between an index of N availability, foliar nitrogen : phosphorus (N : P) ratios, tree defoliation and discoloration. We hypothesized a segmented response of stand health to N : P ratios and an improved model-fit after correcting for climatic covariates.In accordance with the hypothesis, we found a segmented response with a breakpoint for conifer defoliation at N : P ratios as low as 7.3. Inclusion of climatic variables improved the fit of the models, but there was significant collinearity with N : P.Increases in N availability appear, at least for conifers, to have a negative effect on tree health even under N-limiting conditions. Regulation of N-deposition levels is consequently as timely as ever. We propose that increases in tree defoliation, other than resulting in serious plant fitness issues, may represent early diagnostic symptoms of N-addition related imbalances.

The higher mortality rate of the older gypsy moth larval instars was reported in the forest complexes of Belgrade and Valjevo region, in the culmination phase of the new outbreak of the gypsy moth in Serbia. By field and laboratory studies of the causes of their death, the presence of conidia and resting spores of the entomopathogenic fungus Entomophaga maimaiga was reported in the dead caterpillars. This has been the first report of occurrence of this species in Serbia, that is, Serbia is the third European country in which this fungus has been reported. It showed to be a powerful reducer of the population size of the gypsy moth, and in both regions it caused the collapse of the outbreak in 2011.

Pine pitch canker (PPC), caused by the pathogenic fungus Fusarium circinatum (Nirenberg and O' Donnell), is a serious threat to pine forests globally. The recent introduction of the pathogen 2 of 34 to Southern Europe and its spread in Mediterranean region is alarming considering the immense ecological and economic importance of pines in the region. Pines in forests and nurseries can be infected, resulting in severe growth losses and mortality. The pathogen is known to spread in plants for planting and in seeds, and results from recent studies have indicated that F. circinatum may also spread through phoretic associations with certain insects. With this review, we aim to expand the current understanding of the risk of insect-mediated spread of PPC in different parts of Europe. Through the joint action of a multinational researcher team, we collate the existing information about the insect species spectrum in different biogeographic conditions and scrutinize the potential of these insects to transmit F. circinatum spores in forests and nurseries. We also discuss the impact of environmental factors and forest management in this context. We present evidence for the existence of a high diversity of insects with potential to weaken pines and disseminate PPC in Europe, including several common beetle species. In many parts of Europe, temperatures are projected to rise, which may promote the activity of several insect species, supporting multivoltinism and thus, further amplifying the risk of insect-mediated dissemination of PPC. Integrated pest management (IPM) solutions that comply with forest management practices need to be developed to reduce this risk. We recommend careful monitoring of insect populations as the basis for successful IPM. Improved understanding of environmental control of the interaction between insects, the pathogen, and host trees is needed in order to support development of bio-rational strategies to safeguard European pine trees and forests against F. circinatum in future.

The effect of two host plants, Turkey oak (Quercus cerris L) and black poplar (Populus nigra L) on gypsy moth (Lymantria dispar L) development was researched. The effect of host plant was determined based on the parameters which characterize the diet, growth and efficacy of conversion of ingested food of the third instar caterpillars. Along with the effect on development, the effect of host plant on the efficacy of biological preparation based on the bacterium Bacillus thuringiensis var. kurstaki in gypsy moth caterpillar suppression was also researched. The differences in parameters characterizing the diet, growth, and efficacy of ingested food between experimental groups of caterpillars grown on poplar and Turkey oak leaves are explained by the differences in the chemical composition of the leaves of these tree species. The efficacy of Btk preparation is conditioned by the mechanism and content of different groups of defense substances in the leaves of the applied tree species