EFFECT OF POSITION IN THE CANOPY OF BIRD CHERRY ON THE DEVELOPMENT OF COLONIES OF RHOPALOSIPHUM PADI L.

REDIA, XCII, 2009: 175-178 BOGUMIL LESZCZYNSKI (*) - ROBERT KRZYZANOWSKI (*) ANNA GADALINSKA-KRZYZANOWSKA (*) - PAWEL CZERNIEWICZ (*) EFFECT OF POSITION IN THE CANOPY OF BIRD CHERRY ON THE DEVELOPMENT OF COLONIES OF RHOPALOSIPHUM PADI L. (*) Department of Biochemistry and Molecular Biology, University of Podlasie, B.Prusa 12, 08110 Siedlce, Poland; leszczb@ap.siedlce.pl Leszczynski B., Krzyzanowski R., Gadalinska-Krzyzanowska A., Czerniewicz P. Effect of position in the canopy of bird cherry on the development of colonies of Rhopalosiphum padi L. The influence of light intensity, temperature and humidity on the growth and development of colonies of the bird cherry-oat aphid was studied. The south and south-western sectors of the canopy of a clump of bird cherry trees, which were less shaded by ash trees, were the most favourable for R. padi performance. The shoots of the bird cherry in these sectors were longer and developed faster than those in the north-eastern sectors. On the shoots located in the south-western sectors there were bigger colonies of the bird cherry-oat aphid. Of the physical environment of the leaves, light intensity was most closely associated with the growth and development of R. padi colonies on the shoots in the different parts of the canopy. There was also a slight effect of the temperature but no association with either humidity or chlorophyll content of the leaves. KEY WORDS: Rhopalosiphum padi, bird cherry, physical environment, chlorophyll INTRODUCTION The bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae) is one of the most important cereal aphids in Scotland, Scandinavia and Central Europe. It is an oligophagous species that host alternates between woody and herbaceous host-plants (LEATHER et al., 1989). The primary host is bird cherry, Prunus padus (L.) and the secondary hosts are grasses. The life cycle of the bird cherry-oat aphid is well studied, especially its population increase on and migration from bird cherry in spring (DIXON, 1971; Dixon and GLEN, 1971; SANDSTROM and PETTERSSON, 2000). In the eastern part of Poland the bird cherry-oat aphid hatches from winter eggs at the end of March. During the next few weeks the aphid feeds and increases in abundance on the developing shoots and leaves of bird cherry. Then in the middle of May winged migrants develop and migrate to herbaceous secondary host-plants (LESZCZYNSKI et al., 2001). The R. padi life cycle is well studied, especially the development of the bird cherry-oat aphid on its primary host (LEATHER and DIXON, 1981; WIKTELIUS, 1984), its spring migration and development on secondary hosts (LEATHER and DIXON, 1981; DEDRYVER and GELLE, 1982; KUROLI, 1983; WALTERS et al., 1984; LEATHER et al., 1989). It is well known that metabolic changes within the tissues of the primary host induce the spring migration of R. padi (WIKTELIUS, 1984; LESZCZYNSKI et al., 1999, CZERNIEWICZ et al., 2008). The spring migrants of the bird cherry-oat aphid are repelled by the odour (methyl salicylate) of the winter host (GLINWOOD and PETTERSSON, 2000). Some authors indicate that weather conditions, including temperature, rainfall and humidity have an important affect on the development of the bird cherry-oat aphid on its primary and secondary host plants (DEAN, 1974; LEATHER, 1981; LESZCZYNSKI, 1990). Several papers report the development of R. padi populations on the primary host (LEATHER and DIXON, 1981; LEATHER and LEHTI, 1981; LESZCZYNSKI et al., 2001; CZERNIEWICZ et al., 2008), however less attention is paid to the location, distribution and density of R. padi colonies on the primary host. WIKTELIUS (1984) found great variation in the numbers of bird cherry-oat aphids on three different bird cherry trees over a period of three years. Our primary observations also indicate that the abundance the bird cherry-oat aphid in Poland varies from area to area, depending on the location on the primary host and from year to year. The R. padi colonies on the primary host differ in size and there are also un-infested bird cherry trees. This paper reports the results of a study of the effect of position on bird cherry on the growth and development of local colonies of the bird cherry-oat aphid. In addition, the associations between light intensity, temperature and humidity, the distribution of aphid colonies and development of shoots on bird cherry clump were determined. MATERIALS AND METHODS LOCATION The single clump of bird cherry studied was located in Aleksandria Park, Siedlce, in the middle of the eastern part of Poland. The clump of bird cherry was surrounded and over shadowed on the northern and eastern sides by tall ash trees whereas the southern and western sides were more exposed to the elements. Shoots 1.5 m above the ground located in five sectors around of the clump of bird cherry were selected. The locations of the sectors were: 1) northern side, which was in the shade of tall ash trees (N); 2) northeastern side, which was surrounded by tall trees (NE); 3) eastern and southern side, which was less affected by the surrounding trees (ES); 4) southern side, which was surrounded only by low bushes and exposed to the sun (S); and 5) southern and western side, which was also surrounded by the low bushes and exposed to the sun (SW). Received 30 July 2009 Accepted 2 September 2009 Published 1 December 2009

176 B. LESZCZYNSKI ET AL. REDIA, Vol. XCII, 2009 APHID PERFORMANCE The development of colonies of the bird-cherry oat aphid in the five sectors was monitored weekly in 2007, from the appearance of the first fundatrices until the end of the spring migration to secondary host-plants. On each occasion the number of aphids on 10 marked shoots in each sector was recorded and expressed as the average number of aphids per shoot in each sector. FEATURES OF THE SHOOTS The chlorophyll a and b (SPAD units) content of the leaves of the shoots in each sector was measured using a Chlorophyll Meter SPAD-502 (Konica, Minolta). The measurements were taken at intervals throughout the observation period and are for three shoots from each sector. In addition, the average length of the shoots in each sector was determined. The measurements were taken during the peak density of the bird cherry-oat aphid, and are for 10 randomly selected shoots from each sector. PHYSICAL CONDITIONS The light intensity, temperature and humidity at the surface of the leaves of shoots were measured using a TES 1335 Light Meter and 4000NV Weather Tracker (Kestrel). Measurements were made five times a day, at 6 am, 10 am, 1 pm, 6 pm and 10 pm, in each sector. The average daily light intensity, temperature and humidity (from appearance of the first fundatrices to peak in aphid abundance) were calculated and correlated with bird cherry-oat aphid performance. STATISTICAL ANALYSIS The bird cherry-oat aphid performance in the five sectors were correlated (r Pearson s coefficient) with the physical conditions prevailing on the leaves and the chlorophyll content of the leaves. The results were also subjected to analysis of variance (ANOVA) and significance of the differences at p = 0.05% determined (Duncan test). RESULTS The bird cherry-oat aphid performed much better on the shoots in the southern and south-western sectors of the canopy of the clump of bird cherry. The shoots in the other sectors were less suitable for R. padi as only a small percentage of the total aphid population occurred on these shoots. In the sectors where the aphid was abundant there were more fundatrices and they gave rise to bigger colonies, which remained so throughout the period the aphid was on bird cherry (Fig. I). In the most suitable sectors the R.padi population remained high in the southwestern sector until the third decade of April and later in the southern sector. Fig. I Average number of aphids recorded in each of five sectors of the canopy of a clump of bird cherry, P. padus. There was a tendency for the chlorophyll a and b content of the leaves to increase as they aged (tab. 1). This increase paralleled that in the general increase in the population of the aphid. However, there were no significant differences in the quantity of these plant pigments in the leaves of the different sectors. Thus, there was no indication that the differences in R.padi performance in the various sectors were associated with differences in the chlorophyll content of the leaves. There were clear differences in the morphology of the shoots, with those on the north and east sides having darker leaves than on the south and west sides. In addition, the shoots on the south and west sides were much longer than those on the shaded north and east sides (Fig. II). Of the environmental conditions measured only light intensity was closely associated with bird cherry-oat aphid performance in the five sectors. The average light intensity between 10 am and 1 pm at the surface of the leaves of the shoots in south and south-western sectors was about three times greater than in the other sectors (Fig. III). There was also a very strong positive correlation between the average light intensity and average aphid abundance in the five sectors (r 0.9828; n=5). While the performance of R. padi on bird cherry tended to increase with increase in daily air temperature and there were differences in the temperatures recorded in the different sectors there was not a clear relationship between Table 1 Temporal changes the chlorophyll a and b (SPAD values) content of leaves in the five sectors of the canopy of the clump bird cherry, P. padus, during the period when infested with R. padi. Observation date Sectors in the canopy of bird cherry N NE ES S SW 06.04 17.7±0.89 18.7±0.83 16.0 ±0.15 18.6±0.41 20.1±0.44 13.04 18.4±0.83 20.3±0.59 17.2 ±0.74 19.5±0.84 21.9±0.62 20.04 20.6±0.52 22.7±0.77 19.2±1.09 21.9±0.81 24.7±0.44 27.04 22.2±0.59 23.9±1.48 20.3±0.29 22.3±0.74 24.4±0.33 04.05 23.4±0.43 26.2±0.61 21.0±0.15 22.6±0.28 23.9±0.29 11.05 27.9±0.22 27.8±0.20 23.4±0.50 25.9±0.49 26.4±0.61 18.05 27.9±0.25 26.5±1.21 28.9±0.14 26.7±0.68 25.1±0.13 24.05 30.8 ±0.15 30.0±0.22 29.6±0.24 29.5±0.32 29.3±0.39

EFFECT OF POSITION IN THE CANOPY OF BIRD CHERRY ON THE DEVELOPMENT OF COLONIES 177 Fig. II Average length of the shoots measured in each of the five sectors of the canopy of the clump of bird cherry, P. padus. Values not followed by the same letter are significantly different at p = 0.05 (Duncan s test). Fig. III Association between the cumulative number of aphids and light intensity recorded in the five sectors of the canopy of the clump of bird cherry. the average daily temperature and aphid performance in the five sectors. However, aphid performance was associated with differences in the temperatures recorded between 10 am and 1 pm in the five sectors, especially during the two weeks prior to R. padi achieving its peak population density on the primary host. The daily humidity recorded at the surface of the leaves varied by about 2.84% between the five sectors and there was an association between humidity and aphid performance. Generally, the average humidity was slightly higher in the north-eastern sectors in the morning and south-western sectors in the afternoon and evening. DISCUSSION Results presented here indicate that sizes of the colonies of the bird cherry-oat aphid in different parts of the canopy of a clump of bird cherry varied greatly. Inter - pretation of this phenomenon is difficult and complex, since many abiotic and biotic factors influence the development of this aphid on its primary host, interactions between host volatiles and sex pheromones (POPE et al., 2007), the number of winter eggs and their mortality (LEATHER, 1980; LEATHER and LEHTI, 1981) and the activity of predators attacking the eggs and aphids (BODE, 1980; LEATHER and LEHTI, 1982; DEDRYVER, 1983). On the other hand, it is known that R. padi is sensitive to weather conditions, such as temperature, air humidity, rainfall, wind speed and daily light intensity while on its secondary host plants (DEAN, 1974; LEATHER et al., 1989; LESZCZYNSKI, 1990). This report suggests that in a park landscape the development of the bird cherry-oat aphid after hatching from over-wintering eggs was dependant on the location of the aphids within the canopy of a bird cherry tree. In such an environment, the major factor associated with the performance of R. padi was average light intensity at the plant surface. Previous results revealed an association between the performance of the bird cherry-oat aphid on cereal leaves and high light intensities at the leaf surface (LESZCZYNSKI, 1990). The southern and south-western sectors of the clump of bird cherry were less shaded by tall trees and more exposed to high light intensities than other sectors. This is important since high light intensities and/or exposure to strong sun light stimulate the biosynthesis of plant metabolites and positively influence insect physiology. The results presented here indicate that vigorous growth of bird cherry shoots occurred mainly in those sectors directly exposed to the sun.. In addition, it is reported that favourable conditions resulted in the development of large fundatrigeniae, highly fecund apterae and an increase in the number of winged emigrants (LEATHER et al., 1989). It is also well known that intense solar radiation stimulates the biosynthesis of insect biomolecules, including vitamin D (TROJAN, 1985). The other abiotic factors studied generally stimulated the development of R.padi on the primary host. The results accord with those of other papers in suggesting that weather can affect the population development of the bird cherry-oat aphid (LEATHER, 1985; VEGA and WORMER, 2008). However, the differences in temperature and humidity in the five sectors were only weakly associated aphid population density. The only exception was the slightly higher temperature in the south-western sector while the strongest daily illumination, during the last two weeks before R. padi population reached a peak density. Similar tendency was also observed in the chlorophyll a and b content of the leaves. The green pigment content increased as the leaves aged, which increased their photosynthetic potential and resulted in a greater biosynthesis of sugars by the leaves of bird cherry (SYTYKIEWICZ et al., 2008, CZERNIEWICZ unpublished). It may also stimulate the development of winged emigrants, since they need energy for flight, but again there was only a weak association between chlorophyll content of the leaves and the the peak numbers of aphids in the five sectors. In conclusion, the data presented suggest that colonies of the bird cherry-oat aphid differ in size even on the same bird cherry tree. This has received scant attention and is in need of further study especially the chemistry of P. padus in relation to the development of R. padi populations under various environmental conditions. This will increase our understanding the ecology of this aphid on its primary host and enable the timing and size of spring migration and colonisation of the secondary hosts, including cereals, to be more precisely predicted. ACKNOWLEDGMENTS This work was supported by grant no N310 003 31/0264 from the Ministry of Science and Higher Education.

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