•In overwintering population of Corythucha arcuata there is a mortality rate of 65%.•Out of 19% fungal infections found, 70% belonged to Beauveria pseudobassiana.•Naturally occurring B. ...pseudobassiana is effective against C. arcuata.•One fungal isolate can produce 18% higher mycosis value than the other.
The invasive oak lace bug Corythucha arcuata (Say, 1832) (Hemiptera: Tingidae) was first recorded in lowland stands of pedunculate oak (Quercus robur L.) in Eastern Croatia in 2013, from where it expanded to the west causing summer yellowing and intensive chlorotic damages of oak leaves. In 2018, the entomopathogenic fungus Beauveria pseudobassiana Rehner and Humber (Hypocreales: Cordycipitaceae) was isolated from several dead C. arcuata adults found in moss, a typical place for overwintering. The first aim of this study was to estimate the number of overwintering adults per m2 of moss, their natural mortality, and natural infestation by this fungus. Moss and oak lace bugs were collected from oak trees at six different locations in infested forests in Spačva basin. C. arcuata individuals were counted and separated for further analysis and determination of possible fungal infections. Results demonstrated a high rate of mortality among overwintering individuals (65%), with 19% of them infested by various entomopathogenic fungi, of which 70% belonged to B. pseudobassiana. The second aim of this study was to test fungal virulence against C. arcuata under laboratory conditions and to study differences between the isolates. A suspension of conidia (concentration: 1 × 108 conidia/ml) was sprayed on healthy adults of C. arcuata on moss patches. Results showed no difference in mortality rates between the isolates (96–97%), but one isolate produced a mycosis of 49% compared to 32% of the other isolate, with 4% of mycosis in control. The results presented here demonstrate this fungus as an antagonist, and indicate it as a potential candidate for future biological control of this invasive pest.
Research highlights: The pine-tree lappet moth, Dendrolimus pini, can cause serious needle defoliation on pines with outbreaks occurring over large geographical areas. Under laboratory conditions, ...the promising potential of the naturally occurring entomopathogenic fungus Beauveria bassiana was tested against D. pini larvae as a biological control method. Background and objectives: The aim of this study was to investigate the most effective concentration and treatment dose of B. bassiana conidial suspension and how it affected the survival and feeding behavior of the pest. Materials and methods: The first experiment applied the fungal suspension directly on the back of selected larvae, and in the second experiment, sporulating cadavers obtained in the first experiment were placed into Petri dishes with healthy individuals. Different doses per larvae µL and spore suspension concentration spores/µL) were used. The second experiment was designed to investigate the horizontal transmission of fungi by exposing individual caterpillars to a cadaver covered in B. bassiana mycelia. Mortality rates were analyzed by Chi-squared tests using absolute values for total mortality and B. bassiana- attributed mortality. The lethal time and feeding-disruption speed were analyzed with parametric and non-parametric tests with the aim to determine whether statistically significant differences were observed between treatments. Results: Analysis of lethal time revealed that the 20 µL dose and 7.9 × 104 concentration yielded highest mortality, but also the average dieback rate of 9.4 days was significantly faster compared to all other treatments. In order to see whether insects stopped feeding after infection with B. bassiana, larvae weight loss was examined. Results showed that effective treatments induced change in the feeding behavior of infected larvae. The feeding disruption caused by the 20 µL treatment occurred on average 5.5 days after exposure or 3.9 days before the final dieback of larvae.
Entomopathogenic fungi (EPF) in Croatian forests are known only from observations of insect cadavers that show obvious signs of disease. To date, their presence in soils has not been investigated. ...The aim of this study was to investigate their occurrence, diversity, and distribution, and to assess their density in tested soils. Soil samples were collected during 2018, 2019, and 2020 at different localities throughout the country, and analyzed by using a method of isolation of fungi on selective culture media. To assess the density of EPF in tested soils, colonies of individual fungal species were counted and recorded; the results were expressed as the number of colony-forming units (CFU) per gram of dry soil. After morphological and molecular analysis, five entomopathogenic fungal genera were identified: Beauveria spp., Metarhizium spp., Purpureocillium spp., Lecanicillium spp., and Paecilomyces spp. Results also showed that the range of a total EPF colony density in the soil varies from 4 × 103 to 27.4 × 103 CFU g−1. The most common were EPF of the genus Beauveria, which were recorded at four of five locations, and at 16 of 25 sampling points, but the highest average number (density) of colonies belonged to the genus Metarhizium. Since this type of research was never conducted in Croatia previously, this is the first evidence that insect pathogenic fungi are present in soils of different natural forest habitats. Such research can be useful in selecting and utilizing entomopathogens that are suitable for biological pest control in certain target areas.
The oak lace bug (OLB), Corythucha arcuata (Hemiptera: Tingidae), was first identified as an invasive pest in Europe in northern Italy in 2000 and since then it has spread rapidly, attacking large ...forested areas in European countries. The OLB is a cell sap-sucking insect that is native to North America, with Quercus spp. as its main host. Its rapid expansion, successful establishment in invaded countries, and observations of more damage to hosts compared to native areas are most likely due to a lack of natural enemies, pathogens and competitors. In its native area, various natural enemies of OLBs have been identified; however, little is known about the occurrence and impact of OLB pathogens. None of the pathogenic fungi found on OLBs in natural conditions have been identified until now. In this study, we provide evidence of four entomopathogenic fungi that are naturally occurring on invasive OLBs found in infested pedunculate oak forests in eastern Croatia. On the basis of their morphology and multilocus molecular phylogeny, the fungi were identified as Beauveria pseudobassiana, Lecanicillium pissodis, Akanthomyces attenuatus and Samsoniella alboaurantium. The sequences generated for this study are available from GenBank under the accession numbers MT004817-MT004820, MT004833-MT004835, MT027501-MT27510, and MT001936-MT0011943. These pathogenic species could facilitate biological control strategies against OLBs.
Phoretic mites use bark beetles for transportation to new, suitable habitats. Some phoretic mites act as predators and parasitoids of the bark beetles’ immature stages, especially egg and early ...larval stages, and are potential agents for the biological control of scolytine forest pests. Mites live very frequently in relationships with other invertebrates. Many are found in association with various species of bark beetles. Here, a total of 41 specimens of different bark beetles of the genus Ips (Ips acuminatus, Ips sexdentatus and Ips typographus) were studied for presence, species composition, and abundance of phoretic mites. The beetles were collected on dead wood and parts of tree bark of Pinus nigra, Pinus sylvestris and Picea abies in the Black Sea Mountains in Kastamonu and Artin Province of Turkey. A total of nine mite species were found, including Dendrolaelaps quadrisetus, Ereynetes sp., Histiostoma piceae, Paraleius cf. leontonychus, Pleuronectocelaeno barbara., Proctolaelaps hystricoides, Schizostethus simulatrix, Trichouropoda lamellosa and Uroobovellaipidis. All species are identified for the first time within Turkish fauna.
Mediterranean pine engraver, Orthotomicus erosus was never considered as a significant pest in Croatia and did not appear in high population densities until 2017, when it reached outbreak level in ...Aleppo pine stands. The beetle was first detected in Marjan Forest Park, Split, and was soon recorded in other parts of the Dalmatian coast. Soon after the outbreak occurred, we observed that all of the attacked trees exhibit severe blue staining in the sapwood which indicated fungal infection caused by the Ophiostomatales group of fungi. This raised the need to investigate their relationship with O. erosus and the pine decline, and the main aim of this study was to isolate and identify them. Isolates were obtained from adult O. erosus beetles, their galleries, and blue-stained sapwood, and identified according to the morphological characteristics and DNA sequencing. A total of six Ophiostomatales (Ophiostoma ips, O. piceae, Graphilbum cf. rectangulosporium, O. floccosum, Sporothrix pseudoabietina and Ceratocystiopsis cf. minuta) were identified in the study. This is the first record of Ophiostomatales as organisms associated with the pest O. erosus and pine species in Croatia.
Sequoiadendron giganteum Lindl. Buchholz is a long-lived tree species endemic to the Sierra Nevada Mountains in California. Due to its massive size and beauty, S. giganteum is a popular ornamental ...tree planted in many parts of the world, including Europe. Since 2017, scattered branch die-back has been observed on S. giganteum trees in Zagreb, Croatia. Other symptoms included resinous branch cankers, reddish-brown discoloration of the sapwood and, in severe cases, crown die-back. Branches showing symptoms of die-back and cankers were collected from six S. giganteum trees in Zagreb and the aim of this study was to identify the causal agent of the disease. The constantly isolated fungi were identified using morphology and phylogenetic analyses based on the internal transcribed spacer (ITS) of the ribosomal DNA (rDNA), and partial sequencing of two housekeeping genes, i.e., translation elongation factor 1-α (TEF 1-α), and β tubulin 2 (TUB2). The fungi were identified as Botryosphaeria dothidea (Moug.) Ces. and De Not. and Neofusicoccum yunnanense G.Q. Li & S.F. Chen. The pathogenicity test was conducted in a plant growth chamber on S. giganteum seedlings and revealed that N. yunnanense was more aggressive compared to B. dothidea. N. yunnanense was able to reproduce symptoms of canker and die-back and kill plants seven weeks after inoculation whereas B. dothidea produced cankers. To the best of our knowledge, this is the first report of B. dothidea and N. yunnanense causing canker and die-back disease of S. giganteum in Croatia. It is also the first record on the identity and pathogenicity of any fungal species associated with S. giganteum in this country. The study expended the known host range of N. yunnanense to include S. giganteum, which is a valuable ornamental tree in Croatian landscapes. Disease management strategies should be developed to mitigate or reduce the impact of the disease.
The aim of this study is to identify plant lice Cacopsylla pulchella as a new alien insect in the fauna of Albania. In order to assess the potential of this insect as a pest causing damages on trees, ...infestation level assessment was used. In the first decade of June 2020 samples were collected at three locations in Albania, where Cercis siliquastrum is grown. Samples were collected and brought to the laboratory for further analysis. Field research was performed to assess distribution and infestation intensity across various localities. The intensity of infestation was assessed by visual examination and was categorized according to previously determined categories. C. pulchella was confirmed on C. siliquastrum in three localities in Albania. Most of the infested trees had a moderate or high intensity of infestation. Compared to the results of other countries, it seems that the Judas trees are under heavy attack in Albania. Librazhd and Elbansn districts had the highest recorded infestation level. Infested trees found in this study should be inspected in the following years and this alien insect should be further monitored in order to estimate its potential of becoming an invasive pest in this country.
U radu se prikazuje pregled dosadašnjih saznanja o Akutnom odumiranju hrastova (AOH), u svijetu opisanom kao AOD (Acute oak decline). Ova polimikrobna bolest je nedavno otkrivena u Hrvatskoj (2021. ...godine) na poluotoku Pelegrin (otok Hvar), gdje se na stablima hrasta crnike zadnjih nekoliko godina javljaju tipični simptomi: sušenje vrhova krošnje koje prate uzdužne raspukline kore, gdje istodobno ispod kore dolazi do odumiranja tkiva u obliku crnih nekroza. U kasnijoj fazi javljaju se i tekline te se vide izlazne rupe kukaca, a stablo nakon 3-4 godine odumire. Bolest se širi sa stabla na stablo, a krajnja posljedica je masovno sušenje. Uzročnici odumiranja tkiva pod korom su patogene bakterije
Brenneria godwinii
,
Gibbsiella quercinecans
i
Lonsdalea britannica
, a njihovi mogući prijenosnici su krasnici
Agrilus sulcicolis
i
A. olivicolor
. AOH je do sada opisana u Ujedinjenom kraljevstvu, Latviji, Španjolskoj, Iranu i Švicarskoj. Važnost prvog nalaza AOH u Hrvatskoj je što hrast crnika kao autohtona vrsta ima posebno značenjej za Mediteranske šume, a k tome su po prvi puta nađene i vrste krasnika koje do sada nisu potvrđene kao vektori AOH. Posebno se naglašava rizik prijelaza AOH na kontinentalne šume hrasta lužnjaka i kitnjaka, jer za razliku od svih dosadašnjih nalaza AOH u svijetu, lužnjakove i kitnjakove šume u Hrvatskoj su jedine koje su već godinama izložene napadima hrastove mrežaste stjenice (
Corythucha arcuata
). Moguća kombinacija hrastove mrežaste stjenice i AOH mogla bi biti iznimno opasna. Stoga se naglašava promptna primjena mjera zaštite, posebice preventivnih te važnost znanstvenih istraživanja.
The paper presents an overview of current knowledge on Acute Oak Decline (AOD), a polymicrobial disease that was recently discovered in Croatia (in 2021) on the Pelegrin peninsula (island of Hvar). In the last few years typical symptoms have appeared on holm oak trees: dieback of the top of the tree crown, followed by appearance of longitudinal cracks in the bark and black tissue necrosis in the form of black necrosis under the bark. At a later stage, swollen lesions with exit holes of insects on tree stems appear, and after 3-4 years tree dies. The disease spreads from tree to tree, resulting in mass dieback. The causes of tissue necrosis under the bark are pathogenic bacteria
Brenneria godwinii
,
Gibbsiella quercinecans
and
Lonsdalea britannica
, and their possible vectors are jewel beetles
Agrilus sulcicolis
and
A. olivicolor
. AOD has so far been described in the United Kingdom, Latvia, Spain, Iran and Switzerland. The specificity of the first AOD finding in Croatia is that holm oak as a native species has a special significance for the Mediterranean forests, and for the first time other species of jewel beetles that have not been found as AOD vectors have been detected. The risk of AOD transition to continental pedunculate oak and sessile oak forests is particularly concerning, because unlike all previous AOD findings in the world, pedunculate and sessile oak forests in Croatia are the only ones that have been exposed to constant attacks of oak lace bug (
Corythucha arcuata
) for years. The possible synergism of oak lace bug with AOD could be extremely dangerous. Therefore, the prompt application of protection measures, especially preventive ones, together with the importance of scientific research is emphasized.
Prirodni neprijatelji invazivne hrastove mrežaste stjenice, Corythucha arcuata (Heteroptera, Tingidae) do sada su slabo istraživani, no otkriće entomopatogenih gljiva kao uzročnika uginuća odraslih ...jedinki nađenih na području spačvanskog bazena produbilo je potrebu za provedbom entomopatoloških istraživanja. Cilj ovog istraživanja bio je utvrditi brojnost hrastove mrežaste stjenice, prirodni mortalitet i prirodni inokulum entomopatogenih gljiva, odnosno njihovu prisutnost u populaciji računajući prosječan broj prezimljavajućih, mrtvih i zaraženih jedinki u 1 m2 mahovine na odabranim lokalitetima spačvanskog bazena. Istraživanje je provedeno u ožujku 2021. godine, a podaci su uspoređivani s onima iz ožujka 2019. godine. Rezultati su pokazali da na tim lokalitetima postoji određeni pad gustoće populacije ovog štetnika, a prezimljavajuću generaciju bilježi vrlo visoki mortalitet od 64%. Također, utvrđeno je povećanje prirodnog inokuluma entomopatogenih gljiva s 13% na 19% populacije, a u ukupnom udjelu zaraženih jedinki njih čak 75% bilo je zaraženo gljivama roda Beauveria. Navedeno povećanje prirodnog inokuluma ukazuje na redukcijski potencijal entomopatogenih gljiva i ulogu koji ti organizmi imaju u prirodnoj regulaciji populacija hrastove mrežaste stjenice, a koja bi s vremenom mogla biti sve važnija.
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