OCCURRENCE OF CHOREUTIS PARIANA (CLERCK) (LEPIDOPTERA, CHOREUTIDAE) AND ITS PARASITOIDS IN APPLE ORCHARDS IN LUBLIN

Edyta Górska-Drabik

ABSTRACT

Studies on the occurrence of Choreutis pariana (Clerck), the qualitative structure of the parasitoid complex of this phytophagous species, as well as the level of its parasitization, were conducted in Lublin during the 1996-1998 period. As a result of the study 1,167 larvae and pupae of apple leaf skeletonizer were collected and counted; their numbers varied according to the study sites. At the site where pesticides were regularly applied only one pupa of this species was collected. Numbers of Ch. pariana population were reduced by 11 species of parasitic hymenopterans of the Ichneumonidae and Braconidae families and the Chalcidoidea hyperfamily. The dominant species was Triclistus congener Holmgr., its contribution to the whole complex of parasitoids was over 45%. Total parasitization of apple leaf skeletonizer larvae and pupae was nearly 25%.

Key words: apple leaf skeletonizer, apple tree, Choreutis patiana, Hymenoptera – Parasitica, Lepidoptera, parasitization.

INTRODUCTION

Reports concerning the occurrence and biology of Choreutis pariana (Clerck) are very modest and were published in the 20s [3, 10] and the 30s of the 20^th century [7]. Little information is also available on the parasitoid insect complex of this species. The only data in the Polish literature may be found in the reports by Minkiewicz [3] and Olszak [4], whereas the most complete list of parasitoids of this species was presented by Zajanckauskas et al. [11].

The aim of the study was to determine the intensity of occurrence of Ch. pariana and recognition of the qualitative structure of parasitoid insect complex of this phytophagous species and the determination of the level of its parasitization.

MATERIALS AND METHODS

The study was conducted in Lublin during 1996-1998. The material was collected at 5 study sites. The following 3 sites were located in the western part on the outskirts of the city: the Ethnographic Museum of Rural History, Maria Skłodowska Curie Botanical Garden, and a household garden. The fourth site was located in the centre of Lublin – a city centre garden. At these sites pesticides were not applied. The fifth site was at the Agricultural University Experimental Orchard situated in the eastern outskirts of the city and was regularly treated with pesticides. Three to seventeen apple trees were selected at random at each site. Ch. pariana larvae and pupae were collected from leaves within arm’s length in the 10-14 day period between June-October. Collected 797 larvae and pupae were kept in an insectarium. Parasitic hymenopterans were identified by Prof. Bartłomiej Miczulski. The term Hymenoptera-Parasitica was adopted according to the keys edited by Medvedev (1978, 1981, 19 86).

RESULTS

From 1996-1998, a total number of 1,167 Ch. pariana larvae and pupae were collected from all study sites, both on the outskirts and in the city centre of Lublin. During the entire study period this species occurred in the greatest numbers on apple trees growing on the area of the Ethnographic Museum of Rural History. The mean number of larvae and pupae on one tree ranged from 20-60 at this site. Among the sites where chemical treatments were not applied, the smallest numbers of Ch. pariana were observed on apple trees in the household garden in the 1998 growing season – 4 larvae and pupae on one tree, on average. In the orchard of the Agricultural University, where insecticides were regularly applied, only one pupa was collected (tab. 1).

The presence of first generation larvae on apple tree leaves was noted at the end of May and the beginning of June, while the first empty cocoons were observed already in the first ten days of June on leaves. The first moths also emerged in the first ten days of June and until the beginning of July. The first larvae of the second generation were observed from the beginning of July, and moths emerged in August. The greatest number of the second generation larvae was noted at the end of July and the beginning of August. Larvae of the last generation were feeding from the last ten days of August until the middle of September, and the cocoons were noted as late as during the first ten days of October. The first moths from pupae of the third generation emerged at the beginning of September.

The numbers of Ch. pariana population was reduced by parasitic hymenopterans belonging to the Ichneumonidae and Braconidae families and the Chalcidoidea hyperfamily. The total parasitization of larvae and pupae by hymenopterans was nearly 25% during the 3 years of the study. This parasitization varied in individual years. It was only 10% in 1996; whereas in 1997 it was the highest – over 37% and in 1998 reached 28% (tab. 2). The level of parasitization at individual sites ranged from 16% in the city centre garden to over 26% in the Ethnographic Museum of Rural History (tab. 3). Parasitoids of the Ichneumonidae family reduced the numbers of Ch. pariana to the greatest level, over 20%. Parasitoids of the Braconidae family and the Chalcidoidea hyperfamily were less abudant. They parasitized about 2% of the Ch. pariana population. The contribution to the parasitization of parasitoids of th e Ichneumonidae family varied in individual years. In 1997 it was the highest – nearly 31%, whereas in 1996 – only 8%. The contribution to the parasitization of parasitic hymenopterans of the Braconidae family in all the study years remained on a similar level – approximately 2%. The contribution to parasitization of parasitoids of the Chalcidoidea hyperfamily varied in the individual years and ranged from 0.6% in 1996 to over 4% in 1997 (tab. 2).

As a result of rearing of 797 Ch. pariana larvae and pupae, 8 Ichneumonidae species from 6 subfamilies, 2 Braconidae species from 2 subfamilies and 1 species of the Chalcidoidea hyperfamily were collected (tab. 4). Two species of parasitoids – Gelis areator Panz. and Mesochorus sp. are classified as hyperparasitoids. The first of the above-mentioned species may sporadically occur as the first-level parasitoid. The dominant species in the Ch. pariana parasitoids complex was Triclistus congener Holmgr. of the Ichneumonidae family. Its contribution to the whole complex of parasitoids was over 45% and it parasitized approximately 11% of the Ch. pariana population in the study period. The remaining 10 species parasitized nearly 14% of the population of Ch. pariana and the contribution of individual species to the complex of parasitoids varied from 0.1% to over 2% (tab. 4).

On the area of the Ethnographic Museum of Rural History, the greatest number of parasitic hymenopterans – 11species was noted; whereas their total number was 170. In the Botanical Garden, 5 species of parasitic hymenopterans and 22 individual insects were collected, while in the household and city centre gardens – only 4 species of parasitoids at each site. Their numbers were on a similar level – 5 and 6 individual insects respectively (tab. 3 and 4).

DISCUSSION

From the larvae of Ch. pariana present in the orchards in Lithuania, the most numerous complex of parasitic hymenopterans included 27 species, the majority of which belonged to the Icheneumonidae family [11]. In the presented studies, 11 species of parasitic hymenopterans were collected, 10 of which have already been reported by other authors, such as Minkiewicz [3], Zajanckauskas et al. [11] Olszak [4]. Only Itoplectis maculator F. was previously known as a parasite of Swammerdamia pyrella (Vill.) [2] and Archips rosanus (L.) [5].

In Poland, from this host species 7 species of Hymenoptera-Parasitica were identified [3, 4]. In own studies, among all species of parasitoids which were observed, 9 have not been previously reported in Poland from this host (tab. 4).

As a result of rearing of larvae and pupae of apple leaf skeletonizer, specimens of Gelis sp. and Mesochorus sp. of the Ichneumonidae family were also obtained, which are hyperparasitoids and were already reported from this host by Zajanckauskas et al. [11] and Olszak [4].

In present studies, in the complex of parasitoids of Ch. pariana, the dominant species was Triclistus congener Holmgr., which parasitized 11% of the host population and contributed to the complex of parasitoids over 45%. Presented results confirm the hypothesis of Szmidt [8] and Szujecki [9] that in the entomophagous insect complex one species may be of a considerable significance in the regulation of the numbers of the phytophagous species.

In available reports there are only few data concerning the level of parasitization of apple leaf skeletonizer. Olszak [4], quoting Kapustina, reported that the mean parasitization of larvae may reach 24%. The result of presented studies have provided similar data: the mean level of parasitization of the Ch. pariana larvae and pupae collected on apple trees growing in Lublin was nearly 25%.

The natural regulation of population of phytophagous insects depends largely on the effectiveness of their natural enemies, among which hymenopterans constitute a large group. This effectiveness is affected by both the features of the biology of an individual species and environmental conditions, such as: availability of plants for host insect species and suitable places for wintering for adults, and the presence of substitute insect hosts [4]. Environmental pollution, mainly due to industry and traffic, exerts a negative effect on beneficial insects occurring in the urban areas. The avoidance of polluted areas by parasitic hymenopterans was confirmed by Beiger and Woroszyło [1]. Environmental pollution in the studied area probably exerted a considerable influence on the numbers and effectiveness of parasitoids. Urban areas are the most strongly transformed anthropogenic environments, with traffic-related and industrial pollution being the primary cause of this transformation [6].

The level of parasitization, the number of species and density of parasitic hymenopterans varied at individual sites examined. The greatest diversity of parasitic hymenopterans were noticed in the Ethnographic Museum of Rural History. The level of parasitization was also the highest and reached 26%, compared to other sites. The variation in the occurrence of parasitoids, and therefore their contribution to parasitization, was influenced by the presence of host plants for the imagines of parasitoids. In the Ethnographic Museum of Rural History many types of flowering plants were growing near trees, which could be a source of nutrition for them, while at the remaining sites there were no flowering plants and the apple trees were surrounded by regularly mowed grass, vegetable plants or coniferous shrubs.

SUMMARY

During the period of the study (1996-1998), Ch. pariana occurred most numerously on apple trees growing in the Ethnographic Museum of Rural History and the level of parasitization was also the highest at this site.

In the orchard protected by insecticides during the two year period 1996 and 1998 only a single pupa of Ch. pariana was collected, which proved that number of the population of this phytophagous species was on a very low level.

The complex of parasitoids emerged from Ch. pariana comprised of 8 species of Ichneumonidae, 2 species of Braconidae and 1 species of Pteromalidae, while Triclistus congener Holmgr. was the dominant species in the complex of parsitoid insects.

ACKNOWLEDGEMENT

I wish to express my sincere thanks to professor Bartłomiej Miczulski who identified parasitic Hymenoptera.

REFERENCES

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