reported here stem probably from plant secretions col- lected by the bees. Second, propolis waxes can no longer be regarded as being formed always and exclu ...
88 reported here stem probably from plant secretions collected by the bees. Second, propolis waxes can no longer be regarded as being formed always and exclusively by pharmacologically inert constituents. Considering the constituent classes of propolis waxes, the long-chain alicyclic compounds like hydrocarbons and esters are probably devoid of any substantial pharmacological activity, but compounds like the pentacyclic triterpenoids reported here should be considered among the constituents with biological activity. For example, lupeol and α-amyrin are known to be antiinflammatory cAK inhibitors (Hasmeda et al., 1999). ACKNOWLEDGEMENTS The authors acknowledge financial support provided by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) and CNPq (Conselho Nacional do Desenvolvimento Científico e Tecnológico).
REFERENCES HASMEDA, M; KWEIFIO-OKAI, G; MACRIDES, T; POLYA, G M (1999) Selective inhibition of eucatyote protein kinases by anti-inflammatory triterpenoids. Planta Medica 65(1): 14–18. HEPBURN, H R (1986) Honeybees and wax. Springer Verlag; Berlin, Germany: 250 pp. MARCUCCI, M C (1995) Propolis: chemical composition, biological properties and therapeutic activity. Apidologie 26(2): 83–99. MARCUCCI, M C; RODRIGUEZ, J; FERRERE, F; BANKOVA, V; POPOV, S; GROTO, R (1998) Chemical composition of Brazilian propolis from São Paulo state. Zeitschrift für Naturforschung, C53(1/2): 117–119. NEGRI, G; MARCUCCI, M C; SALATINO, A; SALATINO, M L F (1998) Hydrocarbons and monoesters of propolis waxes from Brazil. Apidologie 29(4): 305–314.
Journal of Apicultural Research 39(1-2): 88–89 (2000)
THE EFFECT OF CARBON DIOXIDE ENRICHMENT ON NECTAR PRODUCTION IN MELONS UNDER GREENHOUSE CONDITIONS A DAG; D EISIKOWITCH Department of Plant Sciences, The George S Wise Faculty of Life Sciences, Tel Aviv University, PO Box 39040, Tel Aviv 69978, Israel (Received 25 August 1999, accepted subject to revision 26 November 1999, accepted for publication 10 February 2000)
Keywords: Cucumis melo, melon, nectar, carbon dioxide, sugar, greenhouses, pollination, honey bees, Apis mellifera, Israel Melon (Cucumis melo) is widely grown in greenhouses in the south of Israel, mainly during the winter. The only pollinator used for melons is the honey bee (Apis mellifera) (Dag et al., 1992). The nectar produced in melon flowers under these greenhouse conditions is very dilute, sometimes below the minimum level of attrac-
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tiveness to the honey bee (20% sugar) (Free, 1993; Nukrian & Eisikowitch, 1995; Dag & Eisikowitch, 1999). This situation, mostly occurring in closed greenhouses, creates a problem of low bee activity which results in low fruit set (Dag & Eisikowitch, 1995; Dag & Eisikowitch, 1999). It has been suggested that any improvement in nectar reward might increase the attractiveness of the flowers, which in turn would improve fruit set and yield. Carbon dioxide enrichment has been used by the greenhouse industry for many years to increase crop growth and yield (Wittwer, 1986). The photosynthetic rate of plants grown under elevated CO2 conditions can increase by up to 40% compared to those grown at ambient CO2 and lead to increased carbon fixation in most C3 plant species (Cure & Acock, 1986). The current note presents preliminary results of the effect of carbon dioxide enrichment on nectar production in melon. The experiment was conducted at the Regional Research Station in Hazeva, in the centre of the Arava Valley in the southern part of Israel. A 0.5 acre greenhouse was divided into two parts: ‘control’ sector and ‘enriched’ sector. Melon seedlings were planted on 27 December,1990. In the early flowering stage before the hermaphrodite flowering stage (2 February 1990), in each sector, 70 male flowers were bagged in the morning before anthesis took place. Nectar was collected from 10 flowers for each sample between 09.00 h and 15.30 h; the samples were collected alternately from the two sectors. Nectar was collected and its volume measured with 1 µl micropipettes. The concentration of the nectar was measured with a Bellingham and Stanley hand refractometer, read as an equivalent for sucrose solution. The amount of sugar per flower was calculated according to the Cruden et al. (1983) formula, which transforms the value obtained from the refractometer (as sucrose solution) to a typical nectar content (sucrose, glucose and fructose). The concentration of CO2 in the enriched sector was 1000 ppm in the morning, which reduced to 400 ppm at 13.00 h and then increased to 600 ppm by 15.00 h. Nectar volume increased in the period from the morning to noon (fig. 1). The average nectar volumes from the enriched sector were significantly higher than in the control sector (P < 0.05, by Mann Witney test). However, the sugar concentration in the nectar, ranging from 25% in the morning to 32% in the afternoon, wasn’t significantly different between the two sectors. The similar sugar concentration between the two treatments led to a parallel pattern of higher sugar content per flower in the enriched sector, the average differences between the treatments was 0.1–0.3 mg sugar per flower. It is generally agreed that the current ambient level of CO2 is suboptimal for photosynthesis (Wittwer, 1986)
FIG. 1. Nectar volume in melon flowers under greenhouse conditions. CO2 enrichment compared to normal conditions (control) (means ± s.e.). and that photosynthesis level is related to nectar production (Shuel, 1992). Therefore, the above mentioned findings of increased nectar production in melons in an enriched environment are not surprising. However, it does contradict results obtained for field bean (Vicia faba) (Osborne et al., 1997). It is known from the literature that short exposure to a high level of CO2 causes worker honey bees to switch from hive to field activities at an early age, modifies hoarding behaviour and affects other age-dependent activities. All these findings involved exposure to high levels of CO2 or even to a pure CO2 atmosphere (Nicolas & Sillans, 1989). Our observations did not show evidence of any interference with bee foraging activity in the melon greenhouse caused by the CO2 enrichment. It seems that the level of CO2 used in our study (below 1000 ppm) does not cause any direct damage to the bee. However, improvement in nectar reward can increase the attractiveness of the flowers to the bees, increase pollination activity and consequently increase the fruit set and the yield.
REFERENCES CRUDEN, R W; HERMANN, S M; PETERSONS (1983) Patterns of nectar production and plant-pollinator coevolution. In Bentley, B; Elias, T (eds) The biology of nectaries. Columbia University Press; New York, USA; pp 80–125. CURE, J D; ACOCK, B (1986) Crop responses to carbon dioxide doubling: a literature survey. Agricultural for Meterology 38: 127–145.
DAG, A; EFRAT, C; OPHENBACH, R (1992) [Recommendation for pollination of greenhouse-grown melons by the honey bee.] Hassadeh 63: 270–272 (in Hebrew). DAG, A; EISIKOWITCH, D (1995) The influence of hive location on honey bee foraging activity and fruit set in melons grown in plastic greenhouses. Apidologie 26: 511–519. DAG, A; EISIKOWITCH, D (1999) Ventilation of greenhouses increases honeybee foraging activity on muskmelons, Cucumis melo. Journal of Apicultural Research 38: 169–175. FREE, J B (1993) Insect pollination of crops. Academic Press; London, UK; 684 pp. NICOLAS, G; SILLANS, D (1989) Immediate and latent effects of carbon dioxide on insects. Annual Review of Entomology 34: 97–116. NUKRIAN, R; EISIKOWICH, D (1995) Irrigation in melons and its effect on nectar production and honeybee foraging activity. Hassadeh 65: 78–81 (in Hebrew). OSBORNE, J L; AWMACK, C S; CLARK, S J; WILLIAMS, I H; MILLS, V C (1997) Nectar and flower production in Vicia faba L. (field bean) at ambient and elevated carbon dioxide. Apidologie 28: 43–55. SHUEL, R W (1992) The production of nectar and pollen. In Graham, J M (ed) The hive and the honey bee. Dadant and Sons; Illinois, USA; pp 401–425. WITTWER, S H (1986) Worldwide status and history of CO2 enrichment — an overview. In Enoch, H Z; Kimball, B A (eds) Carbon dioxide enrichment of greenhouse crops. Volume 1. CRC Press Inc; Florida, USA; pp 3–15.
88 reported here stem probably from plant secretions collected by the bees. Second, propolis waxes can no longer be regarded as being formed always and exclusively by pharmacologically inert constituents. Considering the constituent classes of propolis waxes, the long-chain alicyclic compounds like hydrocarbons and esters are probably devoid of any substantial pharmacological activity, but compounds like the pentacyclic triterpenoids reported here should be considered among the constituents with biological activity. For example, lupeol and α-amyrin are known to be antiinflammatory cAK inhibitors (Hasmeda et al., 1999). ACKNOWLEDGEMENTS The authors acknowledge financial support provided by FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) and CNPq (Conselho Nacional do Desenvolvimento Científico e Tecnológico).
REFERENCES HASMEDA, M; KWEIFIO-OKAI, G; MACRIDES, T; POLYA, G M (1999) Selective inhibition of eucatyote protein kinases by anti-inflammatory triterpenoids. Planta Medica 65(1): 14–18. HEPBURN, H R (1986) Honeybees and wax. Springer Verlag; Berlin, Germany: 250 pp. MARCUCCI, M C (1995) Propolis: chemical composition, biological properties and therapeutic activity. Apidologie 26(2): 83–99. MARCUCCI, M C; RODRIGUEZ, J; FERRERE, F; BANKOVA, V; POPOV, S; GROTO, R (1998) Chemical composition of Brazilian propolis from São Paulo state. Zeitschrift für Naturforschung, C53(1/2): 117–119. NEGRI, G; MARCUCCI, M C; SALATINO, A; SALATINO, M L F (1998) Hydrocarbons and monoesters of propolis waxes from Brazil. Apidologie 29(4): 305–314.
Journal of Apicultural Research 39(1-2): 88–89 (2000)
THE EFFECT OF CARBON DIOXIDE ENRICHMENT ON NECTAR PRODUCTION IN MELONS UNDER GREENHOUSE CONDITIONS A DAG; D EISIKOWITCH Department of Plant Sciences, The George S Wise Faculty of Life Sciences, Tel Aviv University, PO Box 39040, Tel Aviv 69978, Israel (Received 25 August 1999, accepted subject to revision 26 November 1999, accepted for publication 10 February 2000)
Keywords: Cucumis melo, melon, nectar, carbon dioxide, sugar, greenhouses, pollination, honey bees, Apis mellifera, Israel Melon (Cucumis melo) is widely grown in greenhouses in the south of Israel, mainly during the winter. The only pollinator used for melons is the honey bee (Apis mellifera) (Dag et al., 1992). The nectar produced in melon flowers under these greenhouse conditions is very dilute, sometimes below the minimum level of attrac-
Negri; Marcucci; Salatino; Salatino
89
Notes and comments
tiveness to the honey bee (20% sugar) (Free, 1993; Nukrian & Eisikowitch, 1995; Dag & Eisikowitch, 1999). This situation, mostly occurring in closed greenhouses, creates a problem of low bee activity which results in low fruit set (Dag & Eisikowitch, 1995; Dag & Eisikowitch, 1999). It has been suggested that any improvement in nectar reward might increase the attractiveness of the flowers, which in turn would improve fruit set and yield. Carbon dioxide enrichment has been used by the greenhouse industry for many years to increase crop growth and yield (Wittwer, 1986). The photosynthetic rate of plants grown under elevated CO2 conditions can increase by up to 40% compared to those grown at ambient CO2 and lead to increased carbon fixation in most C3 plant species (Cure & Acock, 1986). The current note presents preliminary results of the effect of carbon dioxide enrichment on nectar production in melon. The experiment was conducted at the Regional Research Station in Hazeva, in the centre of the Arava Valley in the southern part of Israel. A 0.5 acre greenhouse was divided into two parts: ‘control’ sector and ‘enriched’ sector. Melon seedlings were planted on 27 December,1990. In the early flowering stage before the hermaphrodite flowering stage (2 February 1990), in each sector, 70 male flowers were bagged in the morning before anthesis took place. Nectar was collected from 10 flowers for each sample between 09.00 h and 15.30 h; the samples were collected alternately from the two sectors. Nectar was collected and its volume measured with 1 µl micropipettes. The concentration of the nectar was measured with a Bellingham and Stanley hand refractometer, read as an equivalent for sucrose solution. The amount of sugar per flower was calculated according to the Cruden et al. (1983) formula, which transforms the value obtained from the refractometer (as sucrose solution) to a typical nectar content (sucrose, glucose and fructose). The concentration of CO2 in the enriched sector was 1000 ppm in the morning, which reduced to 400 ppm at 13.00 h and then increased to 600 ppm by 15.00 h. Nectar volume increased in the period from the morning to noon (fig. 1). The average nectar volumes from the enriched sector were significantly higher than in the control sector (P < 0.05, by Mann Witney test). However, the sugar concentration in the nectar, ranging from 25% in the morning to 32% in the afternoon, wasn’t significantly different between the two sectors. The similar sugar concentration between the two treatments led to a parallel pattern of higher sugar content per flower in the enriched sector, the average differences between the treatments was 0.1–0.3 mg sugar per flower. It is generally agreed that the current ambient level of CO2 is suboptimal for photosynthesis (Wittwer, 1986)
FIG. 1. Nectar volume in melon flowers under greenhouse conditions. CO2 enrichment compared to normal conditions (control) (means ± s.e.). and that photosynthesis level is related to nectar production (Shuel, 1992). Therefore, the above mentioned findings of increased nectar production in melons in an enriched environment are not surprising. However, it does contradict results obtained for field bean (Vicia faba) (Osborne et al., 1997). It is known from the literature that short exposure to a high level of CO2 causes worker honey bees to switch from hive to field activities at an early age, modifies hoarding behaviour and affects other age-dependent activities. All these findings involved exposure to high levels of CO2 or even to a pure CO2 atmosphere (Nicolas & Sillans, 1989). Our observations did not show evidence of any interference with bee foraging activity in the melon greenhouse caused by the CO2 enrichment. It seems that the level of CO2 used in our study (below 1000 ppm) does not cause any direct damage to the bee. However, improvement in nectar reward can increase the attractiveness of the flowers to the bees, increase pollination activity and consequently increase the fruit set and the yield.
REFERENCES CRUDEN, R W; HERMANN, S M; PETERSONS (1983) Patterns of nectar production and plant-pollinator coevolution. In Bentley, B; Elias, T (eds) The biology of nectaries. Columbia University Press; New York, USA; pp 80–125. CURE, J D; ACOCK, B (1986) Crop responses to carbon dioxide doubling: a literature survey. Agricultural for Meterology 38: 127–145.
DAG, A; EFRAT, C; OPHENBACH, R (1992) [Recommendation for pollination of greenhouse-grown melons by the honey bee.] Hassadeh 63: 270–272 (in Hebrew). DAG, A; EISIKOWITCH, D (1995) The influence of hive location on honey bee foraging activity and fruit set in melons grown in plastic greenhouses. Apidologie 26: 511–519. DAG, A; EISIKOWITCH, D (1999) Ventilation of greenhouses increases honeybee foraging activity on muskmelons, Cucumis melo. Journal of Apicultural Research 38: 169–175. FREE, J B (1993) Insect pollination of crops. Academic Press; London, UK; 684 pp. NICOLAS, G; SILLANS, D (1989) Immediate and latent effects of carbon dioxide on insects. Annual Review of Entomology 34: 97–116. NUKRIAN, R; EISIKOWICH, D (1995) Irrigation in melons and its effect on nectar production and honeybee foraging activity. Hassadeh 65: 78–81 (in Hebrew). OSBORNE, J L; AWMACK, C S; CLARK, S J; WILLIAMS, I H; MILLS, V C (1997) Nectar and flower production in Vicia faba L. (field bean) at ambient and elevated carbon dioxide. Apidologie 28: 43–55. SHUEL, R W (1992) The production of nectar and pollen. In Graham, J M (ed) The hive and the honey bee. Dadant and Sons; Illinois, USA; pp 401–425. WITTWER, S H (1986) Worldwide status and history of CO2 enrichment — an overview. In Enoch, H Z; Kimball, B A (eds) Carbon dioxide enrichment of greenhouse crops. Volume 1. CRC Press Inc; Florida, USA; pp 3–15.
