Milan Pernek

Phoretic mites of three bark beetles (Pityokteines spp.) on Silver fir

The species composition and abundance of phoretic mites of the bark beetles Pityokteines curvidens, P. spinidens, and P. vorontzowi on Silver fir (Abies alba) were investigated in 2003 at two locations (Trakoscan and Litoric) in Croatia. Stem sections and branches from A. alba trees infested by Pityokteines ssp. were collected and incubated in rearing cages. Bark beetles emerging from the stem sections and branches were examined for photetic mites. A total of ten mite species were documented for the first time as associates of Pityokteines spp. on A. alba. These included Dendrolaelaps quadrisetus, Ereynetes scutulis, Histiostoma piceae, Paraleius leontonychus, Pleuronectocelaeno japonica, Proctolaelaps hystricoides, Schizostethus simulatrix, Tarsonemus minimax, Trichouropoda lamellose, and Uroobovella ipidis. T. minimax was the most frequent phoretic mite of all the three scolytines and U. ipidis was also common, whereas, the other mite species occurred less frequently. The species spectrum and relative abundance of mite associates were similar for all three Pityokteines species. Another species, Pleuronectocelaeno barbara was commonly found phoretic on P. curvidens, captured in pheromone traps in 2005 at the location Litoric. Furthermore, two previously collected mite specimens from Switzerland, phoretic on P. curvidens, were identified as Nanacarus sp. and Bonomia sp. The records from Croatia and Switzerland in the present study increase the number of known mite associates of Pityokteines spp. from one previously documented species to 14 species. None of the phoretic mites found in the survey in Croatia appear to have the potential to be used for biological control of Pityokteines spp., although the feeding habits are unknown for many species recorded.

New associations of phoretic mites on Pityokteines curvidens (Coleoptera, Curculionidae, Scolytinae)

The species composition and abundance of phoretic mites of the bark beetle Pityokteines curvidens caught in pheromone traps were investigated in Croatia. The P. curvidens trapping programs have been in an experimental phase in Croatia since 2004 as a possible monitoring and control system. The trapping program also permits the opportunity to sample phoretic mites found associated with the beetles. Beetles were caught using Curviwit pheromones in Theysohn traps placed in the Litorić region of Croatia. A total of 12 mite species were recovered, including Schizostethus simulatrix, Dendrolaelaps quadrisetus, Histiostoma piceae, H. cf. varia, Paraleius leontonychus, Pleuronectocelaeno barbara, Tarsonemus minimax, Trichouropoda lamellosa, Uroobovella ipidis, Schwiebea sp., Phauloppia lucorum and Dolicheremaeus dorni. Five species, Pl. barbara, Schwiebea sp., H. cf. varia, Ph. lucorum and Do. dorni, are identified for the first time in association with P. curvidens. These findings increase the number of mite species known to be phoretic on P. curvidens from 11 to 16. The present study also increases the number of known mite associates of Pityokteines spp. from 14 to 18.

Success of classical biocontrol agent Torymus sinensis within its expanding range in Europe

Torymus sinensis Kamijo (Hymenoptera, Torymidae), a classical biocontrol agent of chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera, Cynipidae), was released in Croatia, Slovenia and Hungary in 2015. Following the introduction, the research of parasitism rates and population genetic indices on 40 different sites was performed to monitor and evaluate the success of establishment. The observed parasitism rates were unexpectedly high and negatively correlated with the distance from westernmost locality, while population genetic indices showed that populations of T. sinensis did not suffer from bottleneck‐induced founder effect phenomenon. Moreover, lack of genetic differentiation demonstrates that all populations share similar genetic structure, which could be shaped only by high levels of gene flow. We conclude that T. sinensis established viable and genetically diverse populations and successfully spread naturally from Italy across Slovenia to Croatia and Hungary.

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.

Genetic split between coastal and continental populations of gypsy moth separated by Dinaric Alps

The gypsy moth, a polyphagous herbivore species, infests mainly deciduous trees in the northern hemisphere, being invasive in North America. In Croatia, gypsy moth is infesting both continental and coastal forests, with the Dinaric Alps posing a physical migratory barrier between two regions. During outbreaks, caterpillars cause severe damages in both regions, though with different outbreak dynamics, which suggests genetic differences between populations. Representative populations from these two regions were screened by sequencing a region of the mitochondrial COI gene. Ninety‐nine sequences resulted in seventeen haplotypes, and analyses revealed a significant genetic differentiation between coastal and continental populations, quite likely attributed to geographic isolation and post‐glacial history. This differentiation arises from significantly higher genetic variability in Mediterranean population, indicating their higher adaptability, an intriguing fact in case of possible northward range shift of gypsy moth.

NEW CALCULATION OF CRITICAL NUMBER OF GYPSY MOTH ( Lymantria dispar L.) EGG MASSES FOR BETTER POPULATION DENSITY PROGNOSIS

Gubar (Lymantria dispar) je kao stetnik hrastovih suma u Hrvatskoj dominirao do 60-tih godina prosloga stoljeca, otkada su njegove populacije u kontinentalnom dijelu u blagom opadanju, sa ciklickim gradacijama svakih 10-11 godina. Zadnje dvije gradacije zabilježene su 2003-2005 i 2013-2014 godine. U radu se opisuje nov nacin obracuna kriticnog broja jajnih legala gubara, kojim se procjenjuje rizik golobrsta kljucan u prakticnom sumarstvu za donosenje odluke o suzbijanju. Nov nacin obracuna iskazuje kriticne brojeve kao broj jajnih legala po hektaru, za razliku od dosadasnjeg koji se temeljio na broju stabala na kojemu se nalazi barem jajno leglo i prikazivao se kao postotak zaraze. Postotak zaraze dijelio je rizik golobrsta u pet klasa, pri cemu je kriticna Klasa 5 predstavljala zaraženost vise od 50% stabala. Dosadasnjim obracunom nije se uzimala u obzir starost stabla, iako je ona povezana s velicinom krosnje, odnosno kolicinom lisca. Nadalje nije uziman u obzir broj jaja u jajnom leglu. Nov obracun bazira se na broju gusjenica koje imaju potencijal obrstiti stablo hrasta određene starosti dobiven iz podataka iz literature. Preracunavanjem tih ulaznih podataka koristenjem prosjecnog broja jaja u jednom jajnom leglu gubara, koji je dobiven iz 50 uzoraka jajnih legala, te normale koja definira broj stabla hrasta lužnjaka po hektaru, dobivena je formula koji izracunava kriticni broj jajnih legala gubara po hektaru. Na osnovi tih rezultata formirane su tri 3 kategorije rizika temeljene na broju gusjenica koji obrste stablo određene starosti. Svaka od njih razlicito definira potrebu za suzbijanje gubara: Kategorija I- treba tretirati, Kategorija II- iznimno tretirati uz specifican razlog i Kategorija III ne treba tretirati. Kriticna Kategorija I uspoređena je s Klasom 5, odnosno Kategorija II s Klasom IV na podacima iz gradacije 2004. i 2013. godine. Rezultati ukazuju kako je primjenom novog obracuna trosak suzbijanja smanjen za 25%. Uz evidentne prednosti ipak su i u novom obracunu uocene slabosti vezane uz nepoznavanje nekoliko važnih varijabli: stvarni broj stabala po hektaru i stvarni broj intaktnih gusjenica koji se dobiva oduzimanjem parazitiranih i sterilnih jaja od prosjecnog broja jaja u leglu. Jos jedna slabo poznata varijabla prosjecna kolicina lisca koju jedna gusjenica može obrstiti te kolicinu lisca u krosnji hrastova određene starosti koju treba u buducim istraživanjima kvalitetnije definirati.

Limited Genetic Structure of Gypsy Moth Populations Reflecting a Recent History in Europe

The gypsy moth, Lymantria dispar, a prominent polyphagous species native to Eurasia, causes severe impacts in deciduous forests during irregular periodical outbreaks. This study aimed to describe the genetic structure and diversity among European gypsy moth populations. Analysis of about 500 individuals using a partial region of the mitochondrial COI gene, L. dispar was characterized by low genetic diversity, limited population structure, and strong evidence that all extant haplogroups arose via a single Holocene population expansion event. Overall 60 haplotypes connected to a single parsimony network were detected and genetic diversity was highest for the coastal populations Croatia, Italy, and France, while lowest in continental populations. Phylogenetic reconstruction resulted in three groups that were geographically located in Central Europe, Dinaric Alps, and the Balkan Peninsula. In addition to recent events, the genetic structure reflects strong gene flow and the ability of gypsy moth to feed on about 400 deciduous and conifer species. Distinct genetic groups were detected in populations from Georgia. This remote population exhibited haplotypes intermediate to the European L. dispar dispar, Asian L. dispar asiatica, and L. dispar japonica clusters, highlighting this area as a possible hybridization zone of this species for future studies applying genomic approaches.

Foliage maturity of Quercus ilex affects the larval development of a Croatian coastal population of Lymantria dispar (Lepidoptera: Erebidae)

Abstract Gypsy moth (Lymantria dispar) is one of the most important forest pests in the world. Numerous previous studies focused only on different host tree species, but small number of them on foliage age. Since recent genetic analyses showed that there are significant differences between Croatian continental and coastal population we investigated coastal population since there was no previous research. For this research juvenile and mature foliage of Holm oak (Quercus ilex) was used. Larval development was investigated in two laboratory experiments. One experiment involved rearing trials consisting of 50 individual larvae per treatment while a parallel experiment investigated gregarious feeding conditions using 120 larvae in a rearing treatment. Larval mortality was lower and development time shorter for individuals reared on juvenile foliage. High pupation success in both the individual and group rearing experiment for larvae reared on juvenile foliage was also observed. To conclude, our results showed high mortality, poor larval development and low pupation success in larvae reared on mature foliage. This research is significant because in the aspect of ongoing climate changes there is a possibility that gypsy moth will move to the north and shift its distribution by expanding into new climatic area.