LEPIDOPTERA OF HAZEL PLANTS IN POLAND (PART II). THE NATURAL REGULATION OF LEPIDOPTERA SPECIES IN DIFFERENT HABITATS

Magdalena Gantner

ABSTRACT

The species composition of parasitoids and the level of parasitization of Lepidoptera species feeding on hazel shrubs in different habitat conditions was studied during the three years period. Twenty-two species of parasitic hymenoptera (Hymenoptera, Parasitica) and 2 species of diptera (Diptera, Tachinidae) were collected. Even infrequent treatments of insecticides on hazel plantations have limited the population of parasitoids and reduced their species richness. Ichneumonidae (Hymenoptera, Parasitica) played the greatest role in parasitization of leaf rollers, while Lyphia dubia (Diptera, Tachinidae) and Macrocentrus marginator (Hymenoptera, Parasitica) of Operophtera brumata.

Key words: Hymenoptera parasitica, Diptera, Tachinidae, Lepidoptera, parasitization, hazelnut..

INTRODUCTION

Lepidoptera caterpillars, which occur commonly in orchards, are frequently accompanied by a considerable number of natural enemies. Clearly, the greatest importance in the nature is attached to the insects belonging to the orders of Hymenoptera and Diptera. They form one of the most important communities of beneficial organisms occurring in great numbers both in agrocenoses and in the natural environment. Till now the studies were conducted on parasitization of Lepidoptera caterpillars occurring in apple orchards, on currant plantations and on ornamental shrubs in Poland [2, 3, 4, 5, 6, 7, 8]. There is no information on the natural regulation of Lepidoptera larvae in hazel plantations. The present paper is an integral part of the studies concerning the Lepidoptera fauna inhabiting cultivated and wild hazel plants. The purpose of these studies was to find out the species composition of parasitoids and to determine the degree of parasitization of L epidoptera of the larval instars.

MATERIALS AND METHODS

The area of the studies was presented in detail in Part I of publication concerning the occurrence of Lepidoptera larvae on hazel in different environments of eastern Poland. The initial material was composed of Lepidoptera caterpillars collected from hazel shrubs during three vegetation seasons in the years 1994-1996. The rearing of caterpillars was carried out on Petri dishes and in jars. The wintering instars of insects were kept in a fridge or in the insectarium.

RESULTS

Twenty-two species of parasitic hymenoptera (Hymenoptera-parasitica), belonging to 3 families and 11 subfamilies, and 2 species of diptera (Diptera, Tachinidae) were identified. Among the hymenoptera, 10 species has belonged to the family Braconidae, 9 to Ichneuminidae, and 3 to Eulophidae.

General parasitization of Lepidoptera larvae in the course of three years’ studies was over 19%, and depending on the locality it remained at the level of 23% on the protected plantation, 18% on the unprotected one, and 17% in the forest environment (tab. 1). The species composition of parasitoids was also related to the locality.

The greatest number of species and individuals was reared from the larvae of leaf rollers (tab. 2). The majority of parasites belong to this very species, which is connected with a clear domination of Archips rosanus species. Campoplex mutabilis reared from the larvae feeding on the unprotected plantation and in the forest, and Meteorus ictericus from the protected plantation were the most effective. Ichneumons played the greatest part in parasitization of leaf rollers, independent of the localization of the studied site. They limited the population of this family of Lepidoptera by more than 10% on the protected plantation, by 6% on the unprotected plantation, and by 5% in the forest (fig. 1). Parasitoids from the family Braconidae have parasitized 6% of tortricid larvae on average in all the examined objects. Hymenoptera from the family Eulophidae were not observed on the unprotected plantation.

The most frequent representative of Lepidoptera was Operophtera brumata from the family Geometridae on the examined hazel shrubs. It appeared gradually on the unprotected plantation in the years 1994-1995. The most frequent parasite of Operophtera brumata was Lyphia dubia, which in the 1994 parasitized more than a half and in the 1995 almost 20% of the population of this pest (fig. 2). Another parasite of Operophtera brumata was hymenopteron Macrocentrus marginator from the family Braconidae. Besides, ichneumons from the genera Campolex sp., Diadegma armillata and Syspasis eburnifrons, as well as Oncophanes laevigatus; hymenoptera from the genus Apanteles sp., from Braconidae and Eulophus larvarum and hymenoptera from the genus Eulophus spp. from Eulophidae were obtained from the larvae Geometridae collected on the unprotecte d hazel plantation and in the forest environment. Nine species of parasitoids have emerged from the larvae of Lepidoptera belonging to the family Geometridae. The smallest number of parasites was obtained from the larvae of Noctuidae and Lymantriidae but the number of larvae from those families was low on hazel plants.

Representatives of the family Noctuidae mainly belonged to three species, as: Orthosia cerasi, O. cruda and Cosmia trapezina. Their parasites were mainly ichneumons (Ichneumonidae) – Spudastica robusta, Diadegma armilata, Exetasces spp., Braconidae – Macrocentrus linearis, Holombus annulicornis and Microplitis as well as Eulophidae – Eulophus larvarum. The most important representatives of Lepidoptera species from the family Lymantriidae were Lymantria dispar, Calliteara pudibunda and Euproctis chryssorrhoea. Their larvae were hosts of hymenopera from the family of Braconidae: Apanteles spp., Meteorus ictericus as well as from the family Eulophidae – Eulophus spp.

DISCUSSION

Totally, 22 species of parasitic hymenoptera (Hymenoptera Parasitica) and 2 species of the dipterous (Diptera, Tachnidae) were found in the groups of collected caterpillars feeding on cultivated and common hazel in different environmental conditions. Eleven species of parasites were observed on the protected plantation, 13 on the unprotected plantation, and 16 in the forest environment. The majority of the obtained parasites are polyphagous species that can feed on representatives of various families of the order Lepidoptera. Only Spudastica robusta was included in the group of specific hymenoptera connected with the family Noctuidae, and Lyphia dubia is an olyphagous species feeding on the species from the family Geometridae [9].

The natural tendency of entomocenosis to relative species stability can be observed on the example of the processes of self-regulation. Operophtera brumata was found among the hazel pests, which its population was regulated by parasites in a significant degree. Lyphia dubia turned out to be its main enemy. It parasitized more than 53% of the population in the first years of studies. Besides, two species of parasitic hymenoptera, namely Oncophanes laevigatus and Macrocentrus marginator as well as one species of Eulophidae, namely Eulophus larvarum have emerged from O. brumata caterpillars. The complex of these parasitoids reduced the number of Operophtera brumata almost to a zero. Olszak [5] found out a similar percent of this pest’s parasitization, with some differences related to the year and the environment.

The species from the family Tortricidae were the most parasitized group of Lepidoptera species on the plantation of protected hazel. The complex of leaf roller parasitoids has been the subject of a number of studies, e.g. in orchards [1, 2, 3, 6, 7, 8]. Tortricids were parasitized in 24.5% on the protected, and in 11% on the unprotected plantation of hazelnut. The main role in limiting their numbers was played by Ichneumonidae. Similar results were achieved by Miczulski and Koślińska [3], who established the level of parasitization of leaf roller complex in apple orchards of the Lublin area within the range from 3% to 30%. The most effective parasitoids of tortricid caterpillars were Campoplex mutabilis from the family Ichneumonidae, Meteorus ictericus from Braconidae, and Sympiesis viridula from Eulophidae. In the study by Zajanczkaukas [9], all the mentioned above species were mostly noticed as a parasitoids of Archips rosanus.

Comparing the species composition of leaf roller parasitoids on both plantations it can be stated that in spite of chemical treatments the parasitic entomofauna was only slightly greater on the protected plantation than on unprotected one. According to Olszak [5], one of the factors increasing the efficiency of parasitoids is maintenance of small populations of pests ensuring the survival of parasitoids.

In conclusion, it should be stated that species and quantity diversity of the observed parasitoids was modified by habitat conditions, including man’s activity. The great majority of parasitoid complex was made up of polyphagous species, whose effect is connected with low numbers of the phytophagous, which in this case were Lepidoptera caterpillars. Even an infrequent use of insecticides, like on hazel plantations, results in reduction of the population of parasitoids and reduction of the species. Only diversity in the case of leaf rollers, the insecticide treatments had no effect on the level of parasitization of lepidopterous larvae or a diversity of parasitoid species complex.

ACKNOWLEDGEMENTS

I would like to express my deep gratitude Professor Bartłomiej Miczulski for help in identification to species, parasitoids reared from the larvae of Lepidoptera and belonging to the order of Hymenoptera – parasitica and Professor Agnieszka Draber-Mońko for those belonging to Diptera, Tachinidae.

CONCLUSIONS

1. Habitat conditions and man’s activity modified the occurrence of parasitoids belonging to the orders Hymenoptera and Diptera in hazel plantations.

2. Most of the parasitoids are polyphagous or olygophagous species the effect of which was associated with small numbers of the phytophagous hosts.

3. Even infrequent treatment of insecticides on hazel plantations reduced the population of parasitoids and their species diversity.

4. Ichneumonidae played the greatest role in parasitization of tortricid larvae, while Lyphia dubia and Macrocentrus marginator were the most effective parasites of Operophtera brumata.

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