DISTRIBUTION OF Entomophaga maimaiga IN … Silva Balcanica, 15(1)/2014 DISTRIBUTION OF Entomophaga...
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110 Silva Balcanica, 15(1)/2014 DISTRIBUTION OF ENTOMOPHAGA MAIMAIGA IN CENTRAL PART OF SERBIA IN THE PERIOD 2011-2013 Mara Tabaković-Tošić Institute of Forestry – Belgrade Abstract During the period 2011-2013, a high mortality of old larval instars of gypsy moth (Ly- mantria dispar) was reported in forest complexes in some regions of Central Serbia in culmina- tion phase of new pest outbreak. Laboratory studies of dead caterpillars showed presence of conidia, and resting spores of the entomopathogenic fungus Emtomophaga maimaiga were established in them. It has been the first discovery of the fungus in Central Serbia, i.e. Serbia is the third European country in which the pathogen has been reported. It proved to be a powerful reducer of gypsy moth population density, and in many cases it caused the outbreak collapse. Key words: Entomophaga maimaiga, Lymantria dispar, Central Serbia, new re- cords INTRODUCTION Naturally occurring enthomopathogens are important regulatory factors in in- sect populations. The entomopathogenic fungus Entomophaga maimaiga Humber, Shi- mazu and Soper (Entomophtorales: Entomophtoraceae) was isolated and described as a natural enemy of gypsy moth in Japan, where it causes periodical epizootics (Soper et al., 1988). It is also distributed in Pacific parts of China and the Far East of Russia (Hajek et al., 2005), where it considerably contributes to the preservation of low population level of the host. In spite of the fact that E. maimaiga was introduced in North America in 1910- 1911 (Speare, Colley, 1912), its presence in the natural populations of gypsy moth was determined only in 1989 (Hajek et al., 1996), when the pathogen caused pan- demic in several countries (Andreadis, Veseloh, 1990; Smitlei et al., 1996; Reardon, Hajek, 1998). Today Entomophaga maimaiga is very significant pathogen of gypsy moth in North America and Canada (Balser, Baumgand, 2001; Hajek et al., 2005). Bulgaria has been the second country in the world and the first in Europe in which E. maimaiga was introduced successfully (Pilarska et al., 2006). For a period of 10-12 years, E. maimaiga expanded its range (naturally and by introductions) and is now found throughout Bulgaria (Georgiev et al., 2010, 2013; Mirchev et al., 2013). In the period 2011-2013, E. maimaiga was found in the European part of Turkey (Georgiev et al., 2012a), Greece, FYR of Macedonia (Georgiev et al., 2012b; Georgieva et al., 2013) and Serbia (Tabaković-Tošić, 2014; Tabaković-Tošić et al., 2012, 2013).
Transcript of DISTRIBUTION OF Entomophaga maimaiga IN … Silva Balcanica, 15(1)/2014 DISTRIBUTION OF Entomophaga...
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Silva Balcanica, 15(1)/2014
DISTRIBUTION OF Entomophaga maimaiga IN CENTRAL PART OF SERBIA IN THE PERIOD 2011-2013
Mara Tabaković-TošićInstitute of Forestry – Belgrade
Abstract
During the period 2011-2013, a high mortality of old larval instars of gypsy moth (Ly-mantria dispar) was reported in forest complexes in some regions of Central Serbia in culmina-tion phase of new pest outbreak. Laboratory studies of dead caterpillars showed presence of conidia, and resting spores of the entomopathogenic fungus Emtomophaga maimaiga were established in them. It has been the first discovery of the fungus in Central Serbia, i.e. Serbia is the third European country in which the pathogen has been reported. It proved to be a powerful reducer of gypsy moth population density, and in many cases it caused the outbreak collapse.
Key words: Entomophaga maimaiga, Lymantria dispar, Central Serbia, new re-cords
INTRODUCTION
Naturally occurring enthomopathogens are important regulatory factors in in-sect populations. The entomopathogenic fungus Entomophaga maimaiga Humber, Shi-mazu and Soper (Entomophtorales: Entomophtoraceae) was isolated and described as a natural enemy of gypsy moth in Japan, where it causes periodical epizootics (Soper et al., 1988). It is also distributed in Pacific parts of China and the Far East of Russia (Hajek et al., 2005), where it considerably contributes to the preservation of low population level of the host.
In spite of the fact that E. maimaiga was introduced in North America in 1910-1911 (Speare, Colley, 1912), its presence in the natural populations of gypsy moth was determined only in 1989 (Hajek et al., 1996), when the pathogen caused pan-demic in several countries (Andreadis, Veseloh, 1990; Smitlei et al., 1996; Reardon, Hajek, 1998). Today Entomophaga maimaiga is very significant pathogen of gypsy moth in North America and Canada (Balser, Baumgand, 2001; Hajek et al., 2005).
Bulgaria has been the second country in the world and the first in Europe in which E. maimaiga was introduced successfully (Pilarska et al., 2006). For a period of 10-12 years, E. maimaiga expanded its range (naturally and by introductions) and is now found throughout Bulgaria (Georgiev et al., 2010, 2013; Mirchev et al., 2013). In the period 2011-2013, E. maimaiga was found in the European part of Turkey (Georgiev et al., 2012a), Greece, FYR of Macedonia (Georgiev et al., 2012b; Georgieva et al., 2013) and Serbia (Tabaković-Tošić, 2014; Tabaković-Tošić et al., 2012, 2013).
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Since 2011, when E. maimaiga was first discovered in two regions of Ser-bia (Belgrade and Valjevo) (Tabaković-Tošić et al., 2012), intensive researches on the fungus have been conducted in the country. This paper provides data about the presence and impact of the pathogen on gypsy moth populations in central part of Serbia.
MATERIALS AND METHODS
During the period 2011-2013, intensive research was conducted in many for-est areas of Central Serbia, where increased mortality rate of gypsy moth larvae was reported without significant defoliation of attacked stands.
Alive and dead gypsy moth larvae in fourth-sixth instars were sampled from oaks (Quercus spp.) and beech (Fagus sylvatica L.) trees in all sites for laboratory studies to determine the cause of mortality and the presence of conidia and resting spores of the entomopathogenic fungus E. maimaiga.
The collected larvae were transferred to a laboratory and grown in climate chamber. During the experiment, temperature and light conditions were constant (temperature 21°C, light regime - 8 h dark, and 16 h light). The larvae were fed on fresh oak leaves, brought regularly from the sample plots. The food was changed daily.
The dead larvae were placed in Petri dishes with wet filter paper. They were kept 7 days at room temperature, and later were stored in a refrigerator for 2-3 months. The samples were analysed under a light microscope. The evaluation of E. maimaiga infections was recorded as positive when azygospores were detected in the bodies of dead larvae.
RESULTS AND DISCUSSION
The economically harmful insect species Lymantria dispar (Linnaeus) (Lepi-doptera: Erebidae) is one of the major pests of broadleaf forests in Serbia. The out-breaks of gypsy moth, over the 150-year-period occurred 17 times (Tabakovic-Tosic, Jovanovic, 2007), and the 18th outbreak started in 2009-2010.
In some areas of Central Serbia in the period 2011-2013, the culmination phase of the outbreak of gypsy moth occurred. The distribution of egg masses per unit of forests (1 ha) ranged from a few hundred to tens of thousands of hectares, and by the laboratory analysis it was determined that the average number of the vital eggs per a mass was about 500, hatching intensity 97%, and the parasitisation rate was very low (about 3%). Based on these indicators, it was determined that in spring in the period 2011-2013, due to the intensive defoliation by numerous larvae which were hatched, the significant defoliation of the foliage would occur.
In the spring of 2011, 2012 and 2013, the selected forest areas in Central Ser-bia, where the great increase of population size of gypsy moth was reported, were
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observed in detail. On many sites (Fig. 1), it was first observed that there was no considerable damage of the foliage, which would normally be clearly visible. Even at the sample plots where the intensity of the attack was equal to several hundred egg masses per hectare, which implies that the next instar can cause 100 percent de-foliation, the trees looked as if the gypsy moth was in the progradation phase at low population density. In addition, at some sample plots the increased mortality rate of the older larval instars in comparison with the expected one was reported. Logically, the following question was posed: What does prevent the larvae from the intensive feeding and doing harm and what has been killing them? In order to get the answer to this question, the detailed analysis of the possible causes was conducted.
During the field studies in May, June and July in the period 2011-2013, a huge amount of dead gypsy moth larvae in L4-6 instars was found on the trees (Table 1, Fig. 2).
The detailed microscope survey of the sampled dead gypsy moth larvae showed in all of them, without any exception, the presence of the numerous resting spores of entomopathogenic fungus E. maimaiga. In addition, presence of conidia of this pathogen species was reported, but the number of them was considerably smaller (Fig. 3), which is logical since older instars of gypsy moth larvae were collected.
During the field research clear symptoms of a disease caused by baculovirus LdNPV were observed in 2.0-17.1 % of the dead larvae (Table 1). However, during
Fig. 1. Geographical locations of E. maimaiga first recorded in Central Serbia
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Table 1. Gypsy moth larvae mortality analysis
Locality - Re-gion Type of forest Year of the
first record
Gypsy moth attack inten-
sity
Larvae with the symptoms caused by
Entomophaga maimaiga
(%)
Baculovirus LdNPV
(%)
Beograd oaks and beech 2011 severe 85.0 15.0
Valjevo oaks and beech 2011 severe 92.4 7.6
Krupanj beech 2013 severe 94.1 5.9Kučevo beech 2013 severe 93.4 6.6
Kragujevac oaks 2013 medium 87.3 12.7Kraljevo oaks 2013 medium 86.7 13.3Kruševac oaks 2013 severe 98.0 2.0
Vrnjačka Banja beech 2013 high 96.2 3.8Brus beech 2013 high 88.7 11.3Blace beech 2013 high 82.9 17.1
Donji Milanovac beech 2012 severe 94.5 5.5
Negotin oaks and beech 2012 severe 94.0 6.0
Leskovac beech 2013 medium 98.0 2.0
Fig. 2. L. dispar killed by E. maimaiga in Belgrade (A), Donji Milanovac (B) and Blace (C) region
the laboratory microscope analysis the presence of LdNPV was not confirmed, which was expected, since the dead larvae in the decomposition phase were not sampled.
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CONCLUSIONS
Field and laboratory studies of dead gypsy moth larvae showed that entomo-pathogenic fungus Entomophaga maimaiga is distributed in many regions of Cen-tral Serbia: Belgrade, Valjevo, Krupanj, Kučevo, Kragujevac, Kraljevo, Kruševac, Vrnjačka Banja, Brus, Blace, Donji Milanovac, Negotin and Leskovac. This signifi-cant pathogen was proved to be a powerful reducer of population density of gypsy moth in Serbian forests, killing 82.9-98.0 % of the pest larvae in studied sites.
Acknowledgments: The study was partly financed by the Ministry of Science of Republic of Serbia, Project 31070 - SUBPROJECT: ‘New technological methods in the integral protection of for-ests with the focus on the entomopathogenic fungus Entomophaga maimaiga, as the possible solution to the problem of the frequent occurrences of the outbreak of gypsy moth in the forest ecosystems of Serbia’.
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