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First record of the pathogenic fungus Entomophaga maimaiga Humber, Shimazu, and Soper (Entomophthorales: Entomophthoraceae) within an outbreak populations of Lymantria dispar (Lepidoptera: Erebidae) in Croatia

BORIS HRAŠOVEC orcid.org/0000-0003-4172-4593 ; Faculty of Forestry, University of Zagreb, Zagreb, Croatia
MILAN PERNEK ; Croatian Forest Research Institute, Jastrebarsko, Croatia
Ivan Lukić
MARNO MILOTIĆ ; Faculty of Forestry, University of Zagreb, Zagreb, Croatia
DANKO DIMINIĆ ; Faculty of Forestry, University of Zagreb, Zagreb, Croatia
MILIVOJ FRANJEVIĆ ; Faculty of Forestry, University of Zagreb, Zagreb, Croatia
ANN HAJEK ; Cornell University, Department of Entomology, Ithaca NY, USA
ANDREAS LINDE ; University of Applied Sciences, Eberswalde, Germany
DANIELA PILARSKA ; 1_Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, Sofia, Bulgaria; 2_Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, Prague, Czech Republic

Sažetak

Background and Purpose: The last wave of a gypsy moth (Lymantria
dispar) outbreak in Croatia and recent discoveries of its fungal pathogen Entomophaga maimaiga in eastern neighboring countries focused the attention of researchers on the possible presence of this pathogen in local gypsy moth populations. Since the first introduction of E. maimaiga in Bulgaria in 1999, several southeastern European countries confirmed its presence in subsequent years. One unchecked report made by a local forester "of dramatically high mortality in gypsy moth larvae at one locality at the easternmost part of Croatia in early summer 2012" raised the interest in whether E. maimaiga occurred in Croatia even higher. In spring 2013, the gypsy moth outbreak area grew even larger. Large areas were aerially sprayed with a Bacillus thuringiensis kurstaki-based bacterial insecticide and larval development was closely inspected in the field. One of the tasks was to check on the possible presence of E. maimaiga in gypsy moth populations in Croatia, and these results are presented here.

Materials and Methods: The research was conducted during June and
July 2013 throughout the Eastern part of Croatia where gypsy moth populations entered into or continued an ongoing outbreak. From ten selected localities where excessive mortality was observed by local foresters, larval cadavers were sampled fromtree trunks 0,5 – 1,5mabove the ground. Only older larval stages (L4–L6) were sampled due to the period of sampling. The cadavers were placed in Petri dishes on moistened filter paper discs, after which they were stored in the refrigerator on +4 °C for 48 – 72 h. Larval tissue samples were inspected under the light microscope.During the process many images were recorded by digital camera. Measurements of spores and
vegetative stages were made via digital imaging software associated with a
compound microscope. Selected samples of field collected dead larvae were
stored in ETOH for further DNA molecular analysis.

Results: In nine out of ten field samples of dead gypsy moth larvae, either conidia or resting spores of E. maimaiga were confirmed. Depending on collection date, microscopic analysis confirmed both conidia and azygospores or azygospores only. The latter was typically the case when fully dry cadavers were collected towards mid July and later. Spore dimensions were as follows: pear-shaped conidia 24.2–35.8 μm crosswise and 29.5–43.6 μm lengthwise; azygosporees 31.7–47.1 μm diameter. Spore sizes and their general shape varied in accordance with gypsy moth cadaver age in days, time of year when
collecting was done and general weather conditions that prevailed
immediately prior to sampling.Macroscopic symptoms
ofE.maimaiga attackwere already clearly visible in the field,
along with some signs of larval mortality caused by ucleopolyhedrovirus
(NPV), but to a lesser extent. There were very few signs of parasitoid mortality and no visible presence of typical gypsy moth predators like Calosoma sycophanta. Larval mortality that could be assigned dominantly to E. maimaigawas highest in the easternmost localities. By the beginning of June thousands of larvae were hanging head down
on tree trunks and no living larva or viable pupa could be
found in the area.

Conclusions: Based on the field collections and microscopic
analysis, it can be concluded that E. maimaiga, a
pathogen of L. dispar introduced on the European continent,
has been confirmed in Croatia. On the basis of some reports from the previous year, it is reasonable to assume that E. maimaiga appeared at least one year earlier (2012) but this cannot be proved now, in spite of the fact that the location of its possible presence in 2012was somehowlogical as itwas reported fromthe far eastern borderwith Serbia and E.maimaiga alreadywas known to occur in Serbia. Further
targeted research in subsequent years, following the ongoing
gypsy moth outbreak, should give a better picture of the
spread and efficacy of this pathogen within Europe.

Ključne riječi

Gypsy moth; outbreak; pathogen; natural control

Hrčak ID:

110881

URI

https://hrcak.srce.hr/110881

Datum izdavanja:

30.9.2013.

Posjeta: 2.118 *