DOI 10.1515/JAS-2016-0031 J. APIC. SCI. VOL. 60 NO. 2 2016J. APIC. SCI. Vol. 60 No. 2 2016 Original Article EVALUATION OF SELECTED ORNAMENTAL ASTERACEAE AS A POLLEN SOURCE FOR URBAN BEES Anna Wróblewska Ernest Stawiarz Marzena Masierowska* Department of Botany, University of Life Sciences in Lublin, 15 Akademicka, Lublin, Poland 20-950 *corresponding author: [email protected] Received: 27 April 2016; Accepted: 8 November 2016 Abstract Offering more floral resources for urban bees can be achieved by growing ornamental bee plants. The aim of the present study was to evaluate selected Asteraceae (Calendula officinalis ‘Persimmon Beauty’ and ‘Santana’, Centaurea macrocephala, Cosmos sulphureus, Dahlia pinnata, Tagetes patula, Tithonia rotundifolia, and Zinnia elegans) as pollen sources for pollinators. Under urban conditions in Lublin, SE Poland, the investigated plants flowered from late June to the end of October. The mass of pollen produced in florets and capitula was found to be species-related. The highest pollen amounts per 10 florets (10.1 mg) as well as per capitulum (249.7 mg) were found for C. macrocephala. The mass of pollen yielded by a single plant depended on both the pollen mass delivered per disk florets and the proportion of disk florets in capitulum, and the flowering abundance of the plants. A single plant of D. pinnata and a single plant of T. rotundifolia each produced the largest pollen mass. Mean pollen yield per 1m2 of a plot ranged from 6.2 g (Z. elegans) to 60.7 g (D. pinnata). Pollen grains are tricolporate, with echinate exine, medium or small in size. They can be categorised as oblatespherical, spherical, and prolatespherical. The principal visitors to C. macrocephala, C. sulphureus, and C. officinalis were honey bees, whereas bumble bees dominated on T. rotundifolia and D. pinnata. A magnet plant for butterflies was Z. elegans. Among the investigated species, D. pinnata, C. macrocephala, and T. rotundifolia were found to be the most valuable sources of pollen flow for managed and wild bees. Keywords: Asteraceae, bee pasture, pollen production, urban bees INTRODUCTION 2012; Jędrzejewska-Szmek & Zych, 2013). High plant species diversity is characteristic Pollinators provide vital ecosystem services both of several urban areas. Plant species richness to crops and wild plant communities (Aguilar et often increases in cities compared to more al., 2006; Klein et al., 2007). The primary pol- natural areas (Grimm et al., 2008). Therefore, linators of most plants are mainly bees. There urban areas are supportive to wild pollinators. is a clear evidence of recent decline in global The increase in plant richness in cities happens biodiversity and pollinating insects are no by using both native and alien ornamental plant exception (Potts et al., 2010). Land-use change species in landscaping and gardening (Acar et al., with the loss of floral and nesting resources 2007; McKinney, 2008). But replacement with is generally thought to be the most important exotic or alien plants may also be the cause of contributor to various disturbances in wild bee the changes in insect populations (Stelzer et al., abundances and species richness (Winfree et al., 2010). The usefulness of ornamental species 2009). However, current studies have shown and cultivars requires detailed investigations that cities could be pollinator reservoirs with concerning their flowering biology and availabil- a higher biodiversity of pollinating insects within ity of floral rewards. them, as compared to the countryside (Goulson One of the best-represented plant families et al., 2010; Banaszak-Cibicka & Żmihorski, in urban ecosystems is Asteraceae. Many 179 wróblewska et AL. Ornamental Asteraceae as a pollen source for bees Asteraceae have mass flowering, showy inflo- (A). Most of the studied taxa are native to the rescences - capitulum type and floral resources New World. Only Calendula officinalis is probably that attract different and abundant pollinators of European origin. Centaurea macrocephala (Käpylä & Niemelä, 1979; Suryanarayana et appears to be native to the Caucasus region and al., 1992; Bodnarčuk et al., 1993; Wróblewska, the nearby Anatolia region in Turkey (Wagenitz, 1995, 1997; Wróblewska & Stawiarz 2012 a, b; 1975). The selected species are easy to grow Denisow et al., 2014). Due to these character- and highly ornamental and have an extended istics, Asteracean species are frequently used flowering period. to compose flowerbeds in avenues, gardens, The study was conducted from 1999 to 2013 squares, and parks. Ornamental Asteraceae but investigations of each taxon were carried are considered particularly important plants for out for 3 growing seasons (Fig. 1). insect visitors (Strzałkowska, 2006; Wróblewska Experimental plots (each of them 2.5m2) were & Stawiarz, 2012 a). Numerous representatives established on a loess soil with pH 6 - 7 and of the Asteraceae family are described as good were fully exposed to the sun. All plants were melliferous plants, providing both nectar and sown directly into plots. After germination, pollen food for insects from early spring to late the seedlings were thinned to obtain the rec- autumn (Rudnianskaja 1981; Jabłoński, 2000; ommended spacing. For each species, plant Ricciardelli d’Albore & Intoppa, 2000; Kołtowski, density (no. plants per 1 m2) was correlated with 2006; Lipiński, 2010). plant size: T. rotundifolia (2), C. sulphureus (6), The aim of the present study was to evaluate D. pinnata and C. macrocephala (7), Z. elegans eight ornamental Asteraceae species and (10), C. officials (11), and T. patula (20). Fer- cultivars as a source of pollen food for pollinat- tilisation and plant protection followed the ing insects under urban conditions. In particular, commercial recommendations. Investiga- we investigated (a) flowering phenology and tions on Centaurea macrocephala started the abundance of plants, (b) temporal distribution second year after sowing, when fully developed of the floral resources produced by them, and specimens were obtained. we estimated (c) the pollen flow. In addition, Flowering phenology and abundance the spectrum of insect flower-visitors (d) was The observations on phenology of flowering monitored, and (e) the morphological features were carried out on the species/cultivar level of pollen grains from these ornamentals were (Dafni, 1992). The flowering onset and flowering determined, which may be useful during pollen termination were recorded to determine the identification in palynological studies of bee timing and duration of flowering. The florets products. number per capitulum and the number of the successive order capitula per plant were MATERIAL AND METHODS counted to assess flowering abundance. Then, the total number of inflorescences per plant Study area and species was determined. In Dahlia pinnata, all capitula The investigation was carried out on the ex- were counted once, at the end of flowering, as perimental plots of the Department of Botany, it was impossible to separate the successive University of Life Sciences in Lublin, Poland order inflorescences without damaging the (51°14’N, 22°34’E). The following annuals (A) plants. During vegetation season, counts were and perennials (P) were included: Calendula made on 6 to 10 plants of each taxon. officinalis L. ‘Persimmon Beauty’ (A), C. offici- Assessment of pollen production and nalis L. ‘Santana’ (A), Centaurea macrocephala morphology of pollen grains Puschk. ex Willd. (P), Cosmos sulphureus Cav. (A), Total pollen mass available to insects was Dahlia pinnata Cav. (P/A – a perennial grown as determined by the modified ether method an annual), Tagetes patula L. (A), Tithonia rotun- (Warakomska, 1972). In consecutive years of the difolia Mill. S.F. Blake (A) and Zinnia elegans Jacq. study, for each taxon, six samples of 150 mature 180 J. APIC. SCI. Vol. 60 No. 2 2016 Fig. 1. Flowering period of the studied ornamental Asteraceae. The values in brackets mean the length of blooming in days. stamen heads from the capitula of successive The length of polar (P) and equatorial (E) axis orders were collected separately. The anthers was measured (Andrejev, 1926) and the shape were removed from randomly chosen flower as the P/E ratio was classified according to buds and placed on previously-tarred watch Erdtman’s recommendations (1954). glasses. Samples were then moved in an air dryer Insect visitation (SUP-65G Wamed, Poland) at 30°C to dehisce. Observations were carried out during one Then the pollen grains were first washed from vegetation season for the species studied, anthers with 70% ethanol, and subsequently - with the exception of T. patula. Throughout several times with pure ether. The accuracy of peak blooming, insect foraging activity was the procedure was checked using a binocular monitored. The number of working insects per microscope. The empty anthers were removed 1m2 of a plot was counted for 5 minutes, six from the watch glasses. Next, the pollen times every 2 hours, from 8:00 to 18:00 (GMT+2 samples were dried and weighted on a balance h). Counts were made on 3 days when there (WA 34 PRL T A14 MERA-KFM, Poland), allowing was favourable weather. Through observa- a calculation to be made of the mass of air-dried tions we noted 5 insect categories: honey bees pollen. The results were expressed per 10 (Apis mellifera L.), bumble bees (Bombus spp.), florets and then recalculated per capitulum and other bees (non-Apis and non-Bombus), but- plant. Moreover, the pollen mass from 1m2 of terflies (Lepidoptera), and all other insects. For the plot area available to insects was estimated. each plant species, the relative abundance of For this purpose, plant density per 1m2 of a plot these categories was determined. The results and the data regarding the average number were presented as centrograms showing the of capitula on a plant already formed during a percentage of individual insects groups working given growing season were used. on flowers. The dimension of pollen grains (n = 200 per Statystical analysis taxon) was determined based on the glycerol- Descriptive data are presented as means.