APHIDS (HOMOPTERA, APHIDODEA) INHABITING THE SHRUBS OF COTONEASTER DIVARICATUS REHDER ET E. H. WILSON IN THE URBAN GREEN AREA OF LUBLIN. PART I. THE POPULATION DYNAMICS

Bożenna Jaśkiewicz

ABSTRACT

The studies concerning the species composition and population dynamics of aphids inhabiting the shrubs of Cotoneaster divaricatus Rehder et E.H. Wilson were conducted in two sites: street site (A) and park site (B) on the green areas of Lublin in the years 1999-2001. Three species of aphids, namely Aphis pomi De Geer, Aphis fabae Scop. and Rhopalosiphum insertum (Walk.) were found on examined shrubs. All aphids species occurred in greater number in park site (B). A. pomi was the most numerous aphid species in both sites. Hot summer with air temperatures above 30°C and stormy rainfalls clearly decreased number of all aphid species.

Key words: aphids, Aphis pomi De Geer, Aphis fabae Scop., Rhopalosiphum insertum (Walk.), Cotoneaster divaricatus Rehder et E. H. Wilson, population dynamics..

INTRODUCTION

The shrubs of Cotoneaster divaricatus Rehder et E. H. Wilson belong to the more valuable leafy decorative plants in parks, gardens and in the green areas of housing estates [3]. They are characterised by high ornamental properties due to their pale pink flowers, dark red and long lasting fruit as well as the leaves changing their colour into purple red in autumn [3, 4, 15].

Cotoneasters are attacked by various pests, which inhibit the growth and development of plants and lower their decorative value. These pests include for example Lepidosaphes ulmi (L.), Hedya nubiferana Haw. and aphids (Homoptera, Aphidodea). Aphids, which have a stinging-sucking mouth apparatus, find favourable conditions for their development in the polluted city environment [7]. A few aphid species can feed on the shrubs of C. divaricatus, often forming very numerous colonies.

The purpose of the paper was to establish the species composition of aphids inhabiting the shrubs of Cotoneaster divaricatus Rehder et E. H. Wilson and to determine their population dynamics in urban conditions.

MATERIALS AND METHODS

The studies were carried out on Cotoneaster divaricatus Rehder et E.H. Wilson shrubs in the years 1999-2001. The observations included the shrubs growing in the green areas of Lublin in two sites: a street site – A (the area of the Rector’s Office of the Agricultural University) and a park site – B (green area of the Czechów housing district). In both sites, five plants of C. divaricatus growing close to each other were selected. These plants were not subjected to any protective treatment. Five shoots of similar length were chosen on each shrub and aphids were counted there. The plants were monitored between early spring and late autumn, with intervals of about ten days.

The following papers were used to establish the species composition of aphids: [1, 13].

Meteorological data were obtained from the Department of Agrometeorology of the Agricultural University in Lublin.

RESULTS

The presence of three aphid species was found as a result of studies on the shrubs of Cotoneaster divaricatus Rehder et E. H. Wilson: Aphis pomi De Geer, Aphis fabae Scop. and Rhopalosiphum insertum (Walk.).

Figures 1 and 2 present the population dynamics of particular aphid species, and figure 3 shows the weather conditions in the studied years.

Aphis pomi De Geer (photo 1)

After a harsh winter and a cool spring of 1999, the first yellow green aphids A. pomi were observed on the shoots of cotoneaster in the second decade of May in site A (fig. 1), and in the third decade of that month in site B (fig. 2). In subsequent observations the population of aphids increased gradually. Their maximum number in site A was found in the first decade of June (42.2 aphids/shrub), and in the second decade of July in site B (188.4 aphids/shrub). Beginning with the middle of June, a slow decrease of the aphid population was observed in site A, while in site B they occurred with changing intensity. It was probably caused by the heat and stormy rainfalls occurring at that time (fig. 3). The disappearance of aphids in site A took place early, in the third decade of August, while in site B their presence was detected about three months longer, until the first decade of November.

A mild winter and a warm spring in 2000 favoured the development of aphids. The first specimens of A. pomi in site A appeared already in the second decade of April (fig. 1), while in site B – about a month later, in the second decade of May (fig. 2). The subsequent observations showed a considerable increase of the aphid population of this species. In site A, their high number remained between the first decade of May and the end of June, while their maximum was observed in the first decade of June (217.2 aphids/shrub). In site B, the maximum number of aphids were found out in the third decade of June (444.0 aphids/shrub). In site A, between the second decade of July and the second decade of November, the aphids occurred with changing intensity on the examined shrubs, while in site B they stayed till the first decade of October.

After a mild winter in 2001, the first non-winged individuals were observed in site A in the second decade of April (fig. 1), and in site B – about two weeks later, in the first decade of May (fig. 2). In May, the number of A. pomi aphids grew in both sites. Their maximum in site A was found out in the first decade of June (219.4 aphids/shrub), and in site B – in the first decade of July (211.0 aphids/shrub). The decrease of the number of aphids in July was probably caused by high air temperatures (32.5°C) and frequent showers at the end of that month (fig. 3). In August, an increase of the aphid population was found out in both sites, and as early as in September aphids laying eggs were observed (photo 2). The disappearance of A. pomi in sites A and B took place at the same time, in the first decade of December.

Aphis fabae Scop. (photo 3)

Dwarf black specimens of this aphid were observed on the shrubs of C. divaricatus.

In 1999, the periods of occurrence of this aphid species were analogous in sites A and B (fig. 1, 2). The first individuals were observed in the second decade of June and at the same time this was their maximum (in site A – 2.4 aphids/shrub, in site B – 14.2 aphids/shrub). The disappearance of aphids was found out already in the first decade of August. The number of aphids A. fabae in site B was a few times as high as in site A.

In 2000, the presence of this species of aphids was observed only in site B in the course of two observations (in the first decade of June and the first decade of July). Their number in that period was low and did not exceed 2.0 aphids/shrub.

In 2001, seven specimens were found in site A only during one observation. On the other hand, aphids A. fabae in site B were observed between the third decade of May and the third decade of June. They were the most numerous in the second decade of June (6.6 aphids/shrub).

Rhopalosiphum insertum (Walk.)

Aphids of this species appeared only in site B in 2001. Their scarce presence was observed in the course of two observations: in the first and second decade of May (fig. 2).

DISCUSSION

Three years of observations made it possible to state that three aphid species, namely Aphis pomi De Geer, Aphis fabae Scop. and Rhopalosiphum insertum (Walk.) occurred on the shrubs of Cotoneaster divaricatus Rehder et E. H. Wilson.

Aphis pomi De Geer is a frequent species in orchards, especially in tree nurseries [5, 16]. It also inhabits decorative trees and shrubs from the family Rosaceae, for example Chaenomeles sp., Cotoneaster sp. and Crataegus sp. [2, 9, 11, 12, 14]. Aphids of this species appeared annually, between spring and late autumn and they dominated in both sites. Their more numerous presence was found in the park site (B); more than 5,500 specimens were observed on one shrub in the course of three years, while in the street site (A) there were about 3.000 specimens.

Aphids Aphis fabae Scop. preyed on the leaves, young shoots and flower petals in spring and sometimes at the beginning of summer, always being more numerous in the park site. Aphids of this species were dwarf forms (1.2 mm in length) and no paper confirming their occurrence on the examined shrubs was found.

Rhopalosiphum insertum (Walk.) is the species most frequent in orchards in early spring [5]. It is also mentioned by Goszczyński et al. [9] and Łabanowski and Soika [12] on decorative trees and shrubs, i.e. Crataegus sp., Cotoneaster sp. In the present studies, individual specimens of this species were observed only in May of 2001 in the park site.

The effect of weather conditions on the dynamics of aphid population, especially of A. pomi was considerable, causing differences in their numbers. A delayed period of vegetation, frequent stormy rainfalls and heat waves (above 30°C) in July and August did not favour the development of aphids. Such weather conditions were observed especially in 1999, when a smaller population of aphids was observed as compared to the year 2000 (in site A – almost ten times smaller, in site B – 2.5 times). On the other hand, the weather conditions in 2000 and 2001 were more favourable. An early and warm spring with temperatures within the norm, rarer showers and a long period of vegetation caused that the number of A. pomi in those years was considerably higher. The influence of the weather conditions on two other aphids species were minimal because of their occurrence periods. The effect of weather conditions in a given year on the aphid population and the periods of their appearance and disap pearance on other plants are confirmed by the conclusions of a number of authors [5, 6, 8, 10, 17].

CONCLUSIONS

1. Three years of studies on the shrubs of Cotoneaster divaricatus Rehder et E. H. Wilson in Lublin found out the presence of three aphid species, namely Aphis pom De Geer, Aphis fabae Scop. and Rhopalosiphum insertum (Walk.).

2. Larger number of all three species of aphids were observed in the park site (B) as compared to the street site (A).

3. Weather conditions had a significant effect on the number of all aphid species. The aphid population clearly decreased in hot years when the air temperature was above 30°C, or after stormy rainfalls.

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