Karolina Lukášová

Pathogens of Ips amitinus: new species and comparison with Ips typographus

Ips amitinus and I. typographus are two serious pests of spruce in Europe, have similar bionomics and are likely to occur and meet on the same host trees. We therefore hypothesized that the two species support similar levels of similar pathogens. To test this hypothesis, we collected mature beetles from three trap trees at each of eight study sites and determined beetle numbers and pathogen infection levels. In total, 938 mature I. amitinus beetles and 3435 of I. typographus were dissected; five pathogens, as well as intestinal nematodes and endoparasitoids, were detected. The neogregarine Mattesia schwenkei is reported here for the first time as a new pathogen in 9.4% of I. amitinus individuals at one site. Average infection levels of most pathogens (Chytridiopsis typographi, Gregarina typographi, Mattesia schwenkei and parasitoids) were significantly higher in I. typographus than in I. amitinus. Metschnikowia typographi was confirmed only in Ips amitinus, while the microsporidium of Nosema typographi occurred only in I. typographus. Within‐season increases in G. typographi infection levels were documented in Ips amitinus.

Pathogens of the bark beetle Ips cembrae: microsporidia and gregarines also known from other Ips species

The objective of the current study was to identify pathogens of the large larch bark beetle, Ips cembrae, which is a secondary pest that has produced several local outbreaks across Europe in recent years. Beetles were collected from pheromone traps, trap trees and emergence traps (Larix decidua) during 2007 to 2011 at 10 study sites in central Europe. A total of 3379 mature and callow beetles were examined with a light microscope, and only two microsporidian pathogens [Chytridiopsis typographi and a diplokaryotic microsporidium (probably Nosema sp.)] and two gregarines (Gregarina typographi and Mattesia schwenkei) were found. Within the I. cembrae populations, the infection rate for C. typographi ranged from 2 to 58%. Nosema sp. occurred in only two beetles in 2007 (at two study sites). G. typographi was recorded only in Austria and Croatia and only in 1–2% of the beetles in those countries. Mattesia schwenkei was observed solely in Croatia in 0.6% of the beetles in that country. Only one fungal pathogen in the genus Fusarium was found and only in two mature beetles (0.7%) in 2010. The pathogen species found during our study of I. cembrae were very similar to the pathogens previously identified for Ips typographus. No species‐specific pathogen was detected.

Diversity of Ophiostomatales species associated with conifer-infesting beetles in the Western Carpathians

Bark beetles (Coleoptera: Curculionidae, Scolytinae) are commonly recognised as important agents of tree mortality in coniferous forests of the Western Carpathians. They, together with weevils, are consistently associated with ophiostomatoid fungi. Information regarding conifer beetle-associated fungi in the Western Carpathians remains incomplete and unreliable, particularly with respect to fir-infesting bark beetles. This study aims to clarify associations between fungi in the genera Graphilbum, Leptographium, Ophiostoma and Sporothrix (Ophiostomatales) and their beetle vectors in Norway spruce (Picea abies), European larch (Larix decidua) and silver fir (Abies alba). Samples associated with 20 bark beetle species and weevils were collected from nine stands in Poland and the Czech Republic. Fungi were isolated from adult beetles and galleries. Isolates were identified based on morphology, DNA sequence comparisons for four gene regions (ITS, LSU, ß-tubulin, TEF 1-α) and phylogenetic analyses. In total, 46 distinct taxa were identified, including 25 known and 21 currently unknown species. Several associations between fungi and subcortical insects were recorded for the first time. In addition, O. borealis and O. quercus were detected from A. alba for the first time. The composition of the fungal communities varied among the studied tree species and to a lesser degree among the beetle species. The spruce-infesting bark beetles were commonly associated with species of Leptographium s. l. and Ophiostoma s. str.; the larch-infesting bark beetles were often associated with Ophiostoma s. str. and Sporothrix, while the fir-infesting bark beetles were commonly associated with Ophiostoma s. str. and Graphilbum. The most commonly encountered fungal associates of the examined insects were (a) Grosmannia cucullata, G. piceiperda, Grosmannia sp. 1, Ophiostoma macroclavatum and O. piceae with the spruce-infesting bark beetles; (b) O. pseudocatenulatum and Sporothrix sp. 1 with the larch-infesting bark beetles; and (c) O. piceae, Ophiostoma sp. 2 and Graphilbum sp. 2 with the fir-infesting bark beetles. The differences in fungal associates among the bark beetle species occurring on P. abies, L. decidua and A. alba could be linked to the different habitats that these beetles occupy.

Comparison of pathogens infection level in Ips typographus (Coleoptera: Curculionidae) beetles sampled in pheromone traps and at place of overwintering

Abstract The importance of pathogens in the population dynamics of Ips typographus remains a subject of ongoing debate. The main objective of our experiment was to compare the pathogen infection levels of individuals overwintering in bark with the levels of individuals from the same population captured with pheromone traps and thereby to determine primary answers as to whether it can be confirmed that pathogenic organisms affect the flight ability of bark beetles or their ability to leave their places of overwintering. A total of 402 I. typographus individuals were analyzed at a study location under limited management. Three pathogens were confirmed to be present: the gregarine Gregarina typographi, the virus ItEPV, and the microsporidium Nosema typographi. Infection levels of Gregarina typographi and ItEPV were the same in beetles collected at places of overwintering and in those beetles collected in pheromone traps within the immediate vicinity. As these pathogens infect the host’s intestine, the tendency to leave the places of overwintering is apparently not diminished. A similar analysis and comparison of pathogens located in the fat body might bring different results, as our study only detected N. typographi in a single dissected adult spruce bark beetle.

Hollow tree fire is a useless forest fire category

Abstract In the Czech Republic and Slovakia, the term “hollow tree fire“ was first used in a publication in 1956 without being well defined and was then uncritically used in other publications. The term refers to fires occurring in the rotted, inner trunks of trees. The main aim of the current study was to determine whether the term should be considered a useful category for the statistical analysis of forest fires. The nature and causes of fires from 2006–2015 were assessed by performing a detailed analysis of the Fire Rescue Service of the Czech Republic (FRS CR) database. The database included a total of 7,256 fires in the natural environment, but only 18 of these were hollow tree fires. Most hollow tree fires were initiated by human carelessness, and only three were initiated by lightning. Based on our critical consideration of fire attributes, hollow tree fires should not be considered a category of forest fire. The presence of rotten trees is, however, a serious problem because such trees represent long-lasting sources of fire in forest stands and because they complicate firefighting. The numbers of rotten trees in forests is increasing, and firefighters should be made aware of the complications of extinguishing fires involving rotten trees in forests.

Pathogen's level and parasitism rate in Ips typographus at high population densities: importance of time

We compared the levels of pathogen infection in parental beetles, parasitism of the offspring, abundance of predators and breeding performance success of univoltine populations of Ips typographus in plots characterized by short‐term (2–3 years) outbreaks vs. those with long‐term (>10 years) outbreaks on two localities at ca. 1100 m altitude in the Šumava Mts. The numbers of I. typographus were high in all plots, whether the plots were characterized by long‐term outbreaks or short‐term outbreaks. The numbers of maternal galleries in the sample areas ranged from 300 to 400 per m2. The density of parental beetle galleries, abundance of surviving specimens of I. typographus, and length of maternal galleries did not differ between plots. The short‐term outbreaks had only fewer ectoparasitoids of I. typographus and a lower percentage of parasitism and infection level of Mattesia schwenkei than the long‐term outbreaks even though the maternal gallery densities and beetle production were the same. The most mortality appeared to be caused by intraspecific larval competition, and the identical reproductive success in plots with short‐term and long‐term outbreaks indicates that the negative feedback resulting from parasitoids and entomopathogens does not substantially reduce beetle numbers. Although entomopathogenic fungi as Beauveria bassiana occur naturally in the galleries of spruce bark beetles, there was no evidence of its presence in the studied population. The low levels of predation and/or parasitism in both kinds of plots indicate that natural enemies did not play a significant role in reducing outbreak numbers of I. typographus.

Extremely low infection levels of pathogens and nematodes in Trypodendron spp. (Coleoptera: Curculionidae)

Abstract The striped ambrosia beetles Trypodendron lineatum and T. domesticum are timber forest pests in the Palearctic region and North America. Because only a few pathogens are known for Trypodendron species, the aim of this work was to determine the spectrum of pathogen species of T. lineatum, T. laeve, and T. domesticum. Trypodendron species were collected in pheromone traps at nine localities in the Czech Republic, five localities in Poland, and one locality in Austria. In total, 2,439 T. lineatum, 171 T. domesticum, and 17 T. laeve beetles were dissected and examined. Infection was found in only two of the 17 specimens of T. laeve and in only two of the 171 specimens of T. domesticum; in all four cases, the parasites were nematodes. Parasitisation of T. lineatum by nematodes was found in T. lineatum at eight localities with a mean (± SE) parasitisation level of 8.1 ± 4.7%. A Chytridiopsis sp. was detected in cells of the midgut epithelium of one T. lineatum specimen, and Gregarina sp. was detected in the midgut lumen of two T. lineatum specimens; no other pathogens were found in T. lineatum. The low infection rates and the tendency for infection by nematodes can be explained by the monogamy of Trypodendron spp. and their feeding on fungi in short galleries that are not connected to the galleries of conspecifics.

Infection levels of pathogens in the European spruce bark beetle Ips typographus (Coleoptera: Curculionidae) at managed and unmanaged forest locations: a meta-data analysis

Abstract Forest management greatly affects the population density of the European spruce bark beetle, Ips typographus. In this study, a meta-analysis was used to determine whether infection levels of pathogens of I. typographus differ between managed and unmanaged spruce stands. The analysis used data from 10 publications and a total of 61 locations. The results indicated that infection levels of the most common pathogens (ItEPV, Gregarina typographi, and Mattesia schwenkei) are higher in unmanaged than in managed locations. The only exception is the microsporidium Chytridiopsis typographi, which is more common in managed than in unmanaged locations. Our meta-analysis indicates that pathogen levels are generally higher in unmanaged than in managed locations.

Occurrence of Microsporidium sp. and other pathogens in Ips amitinus (Coleoptera: Curculionidae).

A new microsporidium is reported from the small spruce bark beetle, Ips amitinus: Microsporidium sp. with uninucleate oval spores measuring 3.5 × 2.5 μm; infecting cells of the midgut epithelium, midgut muscles, the fat body, the Malpighian tubules, and the gonads of adult beetles collected in Austria. Seven other pathogens were found in beetles collected from Austria, the Czech Republic, and Finland. Six of them were already known from I. amitinus. Nosema cf. typographi is recorded for the first time in the overwintering generation of I. amitinus from the Czech Republic.

Contribution to bionomy of Hylesinus fraxini (Coleoptera: Curculionidae: Scolytinae) and its monogamy in the Czech Republic

Abstract This study focused on bionomics of the ash bark beetle Hylesinus fraxini (Panzer 1779). The study area was at Jílové u Prahy in the Central Bohemian Region of the Czech Republic. In February 2014, three common ash (Fraxinus excelsior) trees were felled and Hylesinus fraxini infestation was subsequently observed from March. Beetles were collected from 20 debarked logs and dissected under stereomicroscope, and their sex was determined. Five logs with bark beetles were placed into photoeclectors. Beetles that emerged were collected and put into the second photoeclector with fresh ash wood to determine whether they would establish the second generation. The analysis showed that each gallery system with a pair of bark beetles contained one male with only one female. If one adult of H. fraxini was found in the gallery system, it was usually female. Therefore, possible polygamy of Hylesinus fraxini was not confirmed in Central Bohemia. Maternal gallery length significantly correlated with the number of eggs laid per female. Offspring beetles did not establish the second generation, as only maturation feeding occurred in fresh wood.