This paper presents research results on forest decline in Serbia. The results were obtained through monitoring defoliation of 34 tree species at 130 sample plots during the period from 2004 to 2018. This research aimed to determine whether the occurrence of defoliation and tree mortality were caused by drought. Defoliation was assessed in 5% steps according to the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) methodology. All the trees recorded as dead were singled out, and annual mortality rates were calculated. To determine changes in air temperature and precipitation regimes during the study period, we processed and analysed climatic data related to air temperature and precipitation throughout the year and in the growing season at 28 main weather stations in Serbia. Tree mortality patterns were established by classifying trees into three groups. The first group of trees exhibited a gradual increase in defoliation during the last few years of monitoring, with dying as the final outcome. The second group was characterised by sudden death of trees. The third group of trees reached a higher degree of defoliation immediately after the first monitoring year, and the trees died after several years. Tree mortality rates were compared between years using the Standardised Precipitation Evaporation Index (SPI) and the Standardised Precipitation Evapotranspiration Index (SPEI), the most common methods used to monitor drought. The most intensive forest decline was recorded during the period from 2013 to 2016, when the largest percentage of the total number of all trees died. According to the annual mortality rates calculated for the three observation periods (2004–2008, 2009–2013, and 2014–2018) the highest forest decline rate was recorded in the period from 2014 to 2018, with no statistically significant difference between broadleaved and coniferous tree species. As the sample of coniferous species was small, the number of sample plots should be increased in order to achieve better systematic forest condition monitoring in Serbia. The analysis of the relationship between defoliation and climatic parameters proved the correlation between them. It was noted that the forest decline in Serbia was preceded by an extremely dry period with high temperatures from 2011 to 2013, supporting the hypothesis that it was caused by drought. We therefore conclude that these unfavourable climatic conditions had serious and long-term consequences on forest ecosystems in Serbia.

In order to reduce negative effects of application of chemical agents, biological control is becoming increasingly important. This paper therefore focused on research of effects of certain types of seed beetles on control of invasive plant species in Serbia. Numerous sources suggest that for legumes and seed beetles Bruhinae: Chrysomelidae the rule of coexistence in pairs applies in all ecozones. The species rely on one another, primarily in terms of geographical origin or association, thus one plant species is frequently attacked by only one type of seed beetle. Being confirmed to be expressly monophagous, bruchins have proven to be excellent potential agents of control of invasive and harmful host plants (to date, false indigo-bush in Serbia), as is the case of the seed beetle of Persian silk tree, which has been registered as monophagous in Serbia for the first time, making it the number one potential agent in control of the host plant – Persian silk tree in Greece. Standard entomological methods were used, from sample collections, to experiments in photo-eclectors, during dissection counting and placing the seed for development inside by the method 1 flacon – 1 seed, to maintain precise records of the origin of the emerged insects and their numbers, within standard laboratory conditions. The conditions favoring the expansion of the plant have already developed due to climatic circumstances (changes in terms of heat extremes – global warming and precipitation), and it is now gradually becoming invasive. Parasitoid accumulation of roughly one-third (30%) of the total number of false indigo-bush pods makes the false indigo-tree seed beetle a viable candidate for the status of a bioagent. The species has the extreme potential for the application of biological measures which is now quickly gaining importance, all for the purposes of developing the integral control of the plants. Species Acanthoscelides pallidipennis and Bruchidius terrenus have been recorded in this research for the first time in Serbia, while calendars of development have been made for the researched bruchin species, which represents a significant scientific contribution.