Native to China, the Asian chestnut gall wasp,
Dryocosmus kuriphilus
(ACGW), was first found outside its native range in Japan and the Korean peninsula in the mid-twentieth century. After appearing ...in North America in 1974, it was found in Europe a few decades later. Since then, the gall wasp has spread throughout the distribution of chestnut in Europe. The ACGW’s discovery in North America and Europe elicited numerous studies to understand its invasive potential in these areas and how to control its spread and impact on chestnut production. Although endemic parasitoids responded positively to
D. kuriphilus
with low parasitism rates, the most effective management tactic has been classical biological control via the introduction of the parasitoid
Torymus sinensis
from its native range in China. This review summarizes the history of introduction, spread, and current distribution of
D. kuriphilus
, and highlights one of the most successful cases of classical biological control against a forest pest.
Arrival, establishment, and further dispersal of non‐native natural enemies are considered essential for a successful biological control programme, while among the factors that may determine the ...success of such a programme, genetic diversity of the introduced population plays an important role in the establishment of a non‐native species.
The Chinese parasitoid wasp Torymus sinensis Kamijo (Hymenoptera: Torymidae) was initially released in Europe in Italy to control biologically the Asian chestnut gall wasp Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), and reduce the damage induced on sweet chestnut (Castanea sativa Miller). In the following years, T. sinensis was then released in numerous other European countries as a biological control agent of D. kuriphilus. Its presence has also been reported beyond the countries of release due to rapid natural dispersal.
To assess the post‐release genetic diversity of D. kuriphilus, we screened T. sinensis populations from six European countries and tested the possibility of these populations suffering from frequently observed genetic effects that could threaten its successful establishment in Europe.
Our results exhibit that T. sinensis populations have suffered neither from the Allee effect nor from genetic bottleneck after their release and establishment in Europe, something that increases the possibility to effectively control D. kuriphilus in Europe.
Background and purpose: Alien invasive species have been described as an outstanding global problem. Hundreds of species are intentionally and unintentionally moved worldwide and and numbers of ...introductions to new habitats have been accelerated all over the world due to the increasing mobility of people and goods over the past decades. Numerous alien insect species, many of them introduced only in the last 20 years, have become successfully established in various ecosystems in Croatia. Box tree moth (Cydalima perspectalis, Lepidoptera; Crambidae) is an invasive pest recently introduced to Europe causing serious damage to ornamental box (Buxus sp.) shrubs and trees. The aim of this paper is to describe the biology of box tree moth with prognosis of its future spread and damages in Croatia.
Material and methods: Young larvae (first and second larval stage) and adults of box tree moth were collected in August and September 2013 in Arboretum Opeka and in Varaždin. They were brought to the entomological laboratory of Croatian Forest Research Institute where they were reared to pupae and then to moths.
Results and Conclusions: The box tree moth was recorded for the first time in North Croatia in August 2013. Larvae were found defoliating box plants (B. sempervirens) in Arboretum Opeka, Vinica and they have been identified as C. prespectalis. According to damages it can be assumed that the pest has been introduced to the region earlier (in 2011 or 2012) and that the primary infection has not been detected. At least two generations per year could be assumed in Croatia in 2013. The damage done to box tree plants on the locality of study is serious. The plants have been defoliated, particularly in the lower parts. The defoliation reduced the amenity value of plants. This is the first record of this pest and its damages in Northern Croatia and it can be expected that the pest will rapidly spread to other parts of Croatia seriously damaging box plants, becoming threat to gardens and parks in Croatia.
Background and Purpose: Orthotomicus erosus, Mediterranean pine engraver, is widely distributed across the Mediterranean and southern Europe, Asia and North Africa. It is considered as secondary pest ...found on recently dead or felled trees, but can also attack weakened living trees. In high population levels this species can attack healthy trees and cause their dieback. Severe outbreaks occur after dry periods, or after fire in adjoining stands in warmer parts of the Mediterranean region, while this scenario has never happened in Croatia up to now. Bark beetles are important forest pests which have already been researched and discussed in relation to climate change, indicating that the predicted increase in temperature would lead to higher survival rates and faster development, thus directly influencing their population dynamics. Increase in temperature may stimulate changes in insects’ rate of development, voltinism, population density, size, genetic composition, extent of host plant exploitation, longitudinal and latitudinal distribution. Since climate conditions might have changed in the last few years as predicted in the Mediterranean region, the aim of our research is to document the first outbreak with high population levels of O. erosus in Croatia.
Materials and Methods: The extent of dieback was evaluated by counting trees with dieback symptoms on diagonal transects plotted through each of 33 forest management sections of Marjan Forest Park (Split). Trunk sections from several trees with early stage symptoms were collected for further laboratory analysis, which consisted of incubation phase and subsequent morphological identification. During regular yearly surveys in forests of Croatia, the pest was observed on several sites and damages were recorded for both years 2017 and 2018. The records were entered into a map using QGIS version 3.2.1-Bonn. Spatial data was downloaded from DIVA-GIS server. Monitoring efforts were initiated in affected areas where 13 flight barrier pheromone traps (Theyson®) equipped with pheromone lure Erosowit® (Witasek, Austria) were set-up in late March in state-owned and privately owned forests across Dalmatia. Catches in the traps were collected and O. erosus adults were counted on a weekly basis in order to identify the abundance of the pest in monitored sites, as well as to obtain the first information about population dynamics and to assess voltinism.
Results: On-site survey and the evaluation of dieback extent included sampling of 5% of all trees in Marjan Forest Park ,and the results showed that 23% of all trees in the forest park were affected by dieback symptoms. Visual examination of trunks, branches and bark showed symptoms of bark beetle infestation, while preliminary on-site examination of the observed adults pointed out to O. erosus. After two weeks in controlled conditions, bark beetle adults started to emerge from trunk sections which were placed in several mesh cages for incubation. Morphological identification by using stereomicroscope and the key for European bark beetles resulted in identification of O. erosus species. Over the course of the year 2017 one more site was reported to be infested with O. erosus, and eight additional sites were reported over the course of year 2018. In total, 446 ha were reported as infested, varying in intensity, in several different management units of state-owned and privately owned forests. The total number of trapped beetles in pheromone traps varied largely among sites. Our data indicate that several generations (at least 5 generations per year) were present in the year 2018.
Conclusions: Sudden surge in observed damages, as well as the number of beetles trapped during monitoring, in years 2017 and 2018 throughout Aleppo pine forests in Dalmatia are the first record of O. erosus outbreak in Croatia. O. erosus is native to Croatia and so far it has been considered only as a minor pest whose outbreaks have never been recorded. Drought intensity and frequency and aridification trends in the research area (Dalmatia, Croatia) cause cumulative stress to trees and have increased O. erosus occurrence. O. erosus is expected to exhibit increased voltinism, better overwintering performance and earlier spring flights. Our first results confirm this epidemic stage of O. erosus with high abundances in Dalmatia in 2018 and at least 5 generations per year, which alter the population level of this pest. Finally, with high dispersal abilities of O. erosus through active flight and easy transportation with infested material (logs and branches with bark), O. erosus has the potential to become an important forest pest in Croatia. Thus, extensive studies on its biology, ecology, natural enemies and interaction with ophiostomatoid fungal species are needed in order to predict further spread and suggest viable and effective management measures.
Corythucha arcuata (Hemiptera; Tingidae), i.e. oak bug is an invasive alien species from North America that has rapidly spread in Europe. It was first reported in Croatia in 2013, and in the ...following years it has spread rapidly toward the west of the continental part of the country, infesting 200,000 ha of Quercus robur L. forest stands. Oak lace bug causes losses in chlorophyll, which has a negative influence on photosynthesis and transpiration activity, as well as on the health status of oak trees. We conducted our study on two sites in the Mediterranean region in Istria, Croatia, where infestation with oak lace bug has not been recorded. Results showed new records of oak lace bug in Istria. Q. pubescens Willd. is the dominant tree species in Sub-Mediterranean forests in Istria, so it will be interesting to follow the spread and preferences of oak lace bug for Q. robur and Q. pubescens in Istria, as well as in other coastal Q. pubescens and Q. ilex L. forests in Croatia. We assume that the negative influence of oak lace bug coupled with other biotic and abiotic stressors in the Mediterranean region will probably have some influence on the health status of oak trees.
The aim of this study is to identify plant lice Cacopsylla pulchella a new alien insect in the fauna of Croatia. We propose a new method of infestation level assessment in order to assess the ...potential of this insect as a pest. In May 2020 samples were collected from eleven locations in Croatia, where Cercis siliquastrum is grown in parks. Adults and nymphs of C. pulchella were collected together with a plant material and brought to entomological laboratory for further analysis. Field research was performed in order to assess the distribution and infestation intensity across various localities in Croatia. The intensity of infestation was assessed heuristically by visual examination and was categorized in four categories: 0) no infestation, 1) low, 2) moderate and 3) high infestation. C. pulchella was confirmed on C. siliquastrum in eleven localities in Croatia. Most of the infested trees had a low or moderate intensity of infestation. Damages caused by this insect are due to the emission of honey dew, a small spherical drop covered with waxy secretion causing necrotic areas which could lead to the premature fall of the leaves. It is not known what kind of progress in infestation intensity could be expected so infested trees found in this study should be checked closely in the coming years. It is strongly suggested to continue the monitoring of this alien insect on C. siliquastrum in Croatia and to estimate its potential of become an invasive pest which could endanger ornamental and other values of its hosts.
Background and Purpose: Dryocosmus kuriphilus is an invasive insect species of sweet chestnut (Castanea spp.) originating from China, and the only effective control measure against this pest is ...classical biological control with introduced parasitoid Torymus sinensis. This parasitoid has been widely released in many European countries, but it also has the ability to rapidly spread naturally. No official releases have been done in Bosnia and Herzegovina.
Material and Methods: D. kuriphilus galls were collected in July 2017 on 6 localities in forest district Unsko (Una Sana canton) in Bosnia and Herzegovina. Presence and parasitism rates of T. sinensis were recorded in the entomological laboratory, Croatian Forest Research Institute. T. sinensis larvae were identified morphologically and by being compared with the voucher specimens.
Results and Discussion: Torymus sinensis larvae were positively identified in the examined D. kuriphilus galls from all localities in Bosnia and Herzegovina. Parasitism rates ranged from 44.83 to 74%. Occurrence and high parasitism rates in Bosnia and Herzegovina observed in this study are not results of biocontrol releases of T. sinensis, but can be attributed to natural spread from Croatia. High parasitism rates observed in this study can indicate that the parasitoid was present in Bosnia and Herzegovina in 2016.
Conclusions: This study presents the first record of Torymus sinensis in Bosnia and Herzegovina. We predict that the parasitoid will continue its spread over Bosnia and Herzegovina in sweet chestnut forests and orchards and that it will act as effective biological control agent against D. kuriphilus.
Background and Purpose: Box tree moth (Cydalima perspectalis: Lepidoptera, Crambidae) is an invasive species rapidly spreading through Europe and making considerable damage to native and planted ...European box plants (Buxus sp.). It has up to three generations per year and has no natural enemies in Europe which helps it to spread rapidly and to become highly invasive in its new range. The aim of this paper is to show i) spatial distribution, ii) number of generations; iii) food choice, and iv) genetic distribution of box tree moth in Croatia.
Materials and Methods: Occurrence data of box tree moth were obtained by field observation and data obtained from the general public. The number of generations of box tree moth was studied by direct observation of life stages on plants. Food choice test was conducted on Buxus sempervirens, Ilex aquifolium, Euonymus japonicus and Ligustrum vulgare used as food plants. Haplotype diversity and distribution of box tree moth was done for 5 localities in Croatia and their comparison to the haplotypes from China, Korea and 10 European countries.
Results: Box tree moth has rapidly spread over the whole territory of Croatia in 4 years and it has three generations per year. The larvae showed a clear preference for B. sempervirens leaves and the total consumption was 0.5 g/dry weight of box leaves/larva. Three haplotypes were observed and haplotype HT4 was found in 4 out of 5 sampling sites in Croatia. The haplotypes observed in Croatia were present in China, which indicates Chinese origin of Croatian populations.
Conclusions: Suitable European climate, widely available host plants and lack of natural enemies have enabled box tree moth to become highly invasive, to quickly disperse in its new environment and to make devastating damages to ornamental European box plants and hedges.
Background and Purpose: Dryocosmus kuriphilus is a globally invasive insect pest, spreading very quickly in new habitats and making serious damage to sweet chestnut forests in Croatia and in several ...other European countries. Indigenous parasitoid species trophically associated with oak gallwasps have adapted to this new host but cannot effectively regulate its population density. Classical biological control using parasitoid Torymus sinensis has been proven to be the only effective method of controlling the populations of D. kuriphilus and has been successfully applied in Japan, South Korea, the USA and Italy. The aim of this review paper is to provide overview and up-to date knowledge about biological control of D. kurphilus and to describe first steps of introduction of T. sinensis to sweet chestnut forests in Croatia.
Conclusions and Future Prospects: Results presented in this paper show adapted biology and behavioural traits of T. sinensis to its host D. kuriphilus. The history and results of introductions of T. sinensis to Japan, the USA, Italy, France and Hungary are shown. The first report of release of T. sinensis to sweet chestnut forests in Croatia is given with discussion on native parasitoids attacking D. kuriphilus. Possible negative effects of T. sinensis on native parasitoid fauna and risks that could influence the successful establishment of T. sinensis in Croatia are discussed. Previous experiences have shown that T. sinensis can successfully control the population density of D. kuriphilus, slowing down the spread and mitigating negative impact of this invasive chestnut pest and keeping the damage of D. kuriphilus at acceptable level. High specificity of T. sinensis suggests that it has limited potential of exploiting native hosts but further detailed monitoring of native parasitoid and possible interactions with introduced T. sinensis is strongly suggested.
•Oak lace bug (OLB) infestation was detected and mapped in Central Europe using MODIS.•New method is presented for decoupling meteorological from the OLB effects on NDVI.•The OLB damage to the forest ...canopy is proportional to the share of oaks in a stand.•The infestation origin in the study area and the speed of OLB spread were determined.•Results indicate that the transportation system is the main driver of the OLB spread.
The oak lace bug (Corythucha arcuata, Say 1832) is a new invasive sap-sucking species in the European oak forests that was first recorded in Central Europe in 2013. It invaded the region from Southeastern Europe, spreads rapidly, and shows no signs of receding after establishment. In this study, focusing on the oak forests in the transboundary area of Hungary and Croatia, we applied two novel methods for detecting and assessing the impact of the oak lace bug (OLB) during the period 2000–2019 based on MODIS NDVI measured at 250 m spatial and 8-day temporal resolution. The first detection method is based purely on NDVI and has the potential to be used in near real-time detection. The second one, based on the residual Z-score of the NDVI models using daily meteorological and soil water content data as independent variables, aims at improved OLB damage assessment by decoupling the effects of the OLB from those caused by the environmental drivers. The presented detection methods had 61.1% to 93.8% agreement with the in situ data, with a better agreement in forests with high oak share. The overall share of the false-positive OLB detections for the strictest method of model residuals was 1.8%. The results confirmed a strong and year-to-year persistent NDVI decrease (down to -14.5% in pure oak forests) during the late summer which can be attributed to the OLB. The origin of the infestation in the study area was identified to be near a resting station on the major highway from Southeastern to Western Europe, corroborating the assumptions that the OLB spread was primarily facilitated by the transport system. The detected speed of the OLB radial spread in the first 3 years of infestation was under 6 km y-1, but since then it increased to above 50 km y-1.
Display omitted
PDF
