Maataloustieteellinen A ikakauskirja Vol. 62: 45—49, 1990 Effect of bee pollination on yield and yield components of field bean (Vicia faba L.) ANNA-LIISA VARIS & RAIJA BRAX 1 Department of Agricultural and Forest Zoology, University of Helsinki, SF-00710 Helsinki, Finland Abstract. The effect of bees on the yield of field bean (Vida faba L.) was studied in cage experiments in southern Finland during two successive years. Comparisons were made between field cages with and without honeybees and open-pollinated uncaged controls. Effect of shad- ing was also considered. The yield in open plots, which were freely visited by pollinators, was considerably greater than in plots from which the insects were excluded. Freely visited plants and plants caged with bees produced about twice as many seeds as plants caged without bees, and the number of seeds per pod was also higher. The plants were tallest in cages without bees. In open plots, 44 % of the bee visitors were honeybees, 56 % being bumblebees. The higher number of seeds obtained with honeybee pollination indicates that honeybees are able to pollinate the field bean flowers in the conditions prevalent in Finland. It is con- cluded that there is little value in introducing bee colonies in small field bean areas and places where bumblebees are fairly abundant. Honeybees may improve the yield in larger fields, where natural pollinators are often scarce. Index words: bee pollination, Vida faba, honeybees, bumblebees Introduction Field bean has been cultivated in Finland since the 16th century. At the moment its acreage is rather small, being only 70 to 100 hectares. In the recent years there has, how- ever, been increasing interest in cultivating Present address: Vaasankatu 14 B 32, SF-00500 Hel- sinki, Finland the field bean, and it has been taken into the breeding programme (Hovinen 1988). The protein content of the seeds is relatively high, as is the content of lysine, an amino acid, which makes beans suitable for use in diets based mainly on lysine-deficient cereals (Clarke 1970). The field bean may also be useful as a break crop in farms with inten- 45 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND sive cereal production. It could be more wide- ly grown as an important source of home- produced feed protein if its yields were more stable. The variations in yield are great (e.g. Varis et ai. 1982), which may partly be caused by weather conditions and susceptibil- ity to pests and diseases; yield variations may also result from problems with pollination (e.g. Lawes 1974). Considerable yield increases caused by hon- eybees have been reported for the field bean (e.g. Scriven et al. 1961, Poulsen 1974), a plant where both self-pollination and cross- pollination occur. The increases in yield, how- ever, vary considerably in studies performed under different conditions, and according to Free & Williams (1977), the pollination re- quirements are well worth studying for each type of conditions. The aim of the present study was to clarify the effect of pollination by bees on the podding and yield of field bean in southern Finland. Materials and methods Field trials were carried out on the Viikki Experimental Farm of the University of Hel- sinki (61°12'N)in 1979 and 1980. Spring sown bean (cf. Mikko, Hankkija, Finland) was used with rows 12.5 cm apart. The treatments were: 1. Plants covered by a cage containing honey- bee colony 2. Plants covered by a cage to exclude the in- sects 3. Plants not caged 4. Plants covered by a cage with only two walls (in 1980 only) Nylon screen cages with an area of 2 m x 2 m and a height of 1.5 m were placed over the plants just before flowering. Randomized plot design with three replicates was used. The distance between plots was 4 m. The total field bean area was 800 square metres in 1979 and 500 square metres in 1980. In 1980 a field bean area of 3500 square metres was situated at 50 m distance from the experimental field. In 1980 a further treatment was added in which the plants were covered by a cage with only two walls. The purpose of this treatment was to clarify the role of the possible shading effect of the cages. For yield data, the total bean yields of the plots were weighed, and the numbers of pods and seeds per pod were counted from 4x5 plants per plot. To obtain the percentage of flowers producing pods, the number of flow- ers in these plants was counted twice a fort- night during the flowering period in 1979, but because this work was highly time-consuming, in 1980 the counting was based on the scores left by the flowers, and it was done immedi- ately after the harvest. The yield data were analysed by the analysis of variance. In 1980 the numbers of honeybees and bumblebees were calculated three times per day (between 9 and 10 a.m., 12 and 1 p.m., 3 and 4 p.m.) per 2 square metres in the centre of the field bean area. Only “positive” polli- nators which visited the front of the flower for nectar and pollen were counted. Results Seed yields. In 1979 the yields from non- caged plots averaged 3600 kg per hectare and in 1980, when the yield ripened too early be- cause of the drought, only 400 kg per hectare. In both years the highest yields were obtained from the non-caged plots. In spite of the great differences in yield, the tendency between the plots caged with bees and those caged with- out bees, in favour of the former, was the same in both years (Table 1). In the second year the yield in shading cages was 68 % of that of the non-caged plots. The seed weight of field bean grown in the open field was greatest. Number of seedsper plant was considerably smaller in plots without pollinators than in open plots or in plots with bees. In shaded plots the number of seeds per plant was about the same as in the open field. Number of seeds per pod was lowest in the plots where the pollinators were excluded. Percentage of flowers producing pods. Most of the flowers did not produce pods. The 46 Table I. Effect of bees on the yield and growth of field bean. Plants caged Plants in without with open shaded bees bees plots plots Seed yield Ist year 1623.8 1875.0 3567.0 kg/ha 2nd year 46.8 114.8 399.2 273.0 mean 835.3» 994.9* 1983.3" 1000 seed Ist year 224.5a 201.6» 421.0" weight g 2nd year 51.6a 45.4" 64.3" 63.6 No. of pods Ist year 5.8 7.2 9.7 per plant 2nd year 1.4 3.4 4.1 3.5 mean 3.6" 5.3» 6.9» No. of seeds Ist year 16.2 28.8 28.9 per plant 2nd year 3.1 9.9 12.0 12.1 mean 9.7» 19.6" 20.5" No. of seeds Ist year 2.7 3.2 3.0 per pod 2nd year 2.3 2.9 2.9 3.4 mean 2.5» 3.0" 3.0" % of flowers Ist year 16.3 18.6 22.8 producing 2nd year 17.6 32.0 39.4 38.0 pods mean 17.0» 25.3» 31.1» Height of Ist year 116.1 108.7 97.5 plants cm 2nd year 54.2 58.4 51.5 53.2 mean 85.2» 83.6» 74.5" Means followed by different letters within the same row are significantly different (P < 0.05, Duncans multiple range test). Interaction treatments x years was significant (P<0.05) only in 1000 seed weight. pod-flower ratio was lowest in plots where the pollinators were excluded. In open plots, which correspond to the normal growing con- ditions, the proportion of pods/flowers was 23 % in 1979 and 39 % in 1980. Height of the plants. In non-caged plots the plants were significantly shorter than in other treatments. Pollinators. 43.6 % of the bee pollinators in the open plots were honeybees, the rest bumblebees. Long-tongued species, B. subter- raneus (L.) and B. hortorum (L.) and to some extent also B. lucorum (L.), were the visitors. Discussion The yield in open plots freely visited by pollinators was more than twice as high as in plots from which insects were excluded. The level of bumblebee and honeybee activity in these plots was rather high to affect the yield through effective cross-pollination. The yield in plots caged with bees was higher than the yield in plots from which the insects were excluded. The difference was, however, not significant, which indicates that it is diffi- cult to arrange natural conditions for bees in cages and to maintain the optimal amount of bees in them. The results are in accordance with those of Free (1966), who blaimed the detrimental effect of caging, which “is likely to minimize any differences in seed produc- tion,” and suggested that the beneficial effect of bee pollination would probably be greater than implied by the results. The shading ef- fect of the cages alone does not explain the differences, because the yield in shading cages was more than twice as great as in the cages with bees and several times greater than in the cages from which the pollinators were ex- cluded. The total area of field bean may also affect 47 the results. In our experiment the total area of field bean was rather small allowing the bumblebees, as more effective pollinators, to achieve adequate pollination in the open plots. In large field bean areas the number of wild bees would most likely be smaller which would emphasize the role of honeybees. Bond and Pope (1974) noticed that crossing decreased as field size increased. In eastern England the critical size above which the number of wild insects would not be sufficient was, however, as high as between 12 and 32 ha. There are different opinions about the ef- fect of plant density on the crossing frequency of field bean (e.g. Fyfe 1954, Homola 1973). In any case, the highest yields from spring- sown field bean are generally obtained with narrow rows (12 —18 cm) (e.g. McEven 1973, Bengtsson and Bingefors 1975). The number of seeds per plant was the same in the bee cages as in the open plots, and it was twice as high as in plots without polli- nators. The greater number of seeds per pod in bee cages and open plots is in accordance with the results of Free (1966) and Poulsen (1974). Although the honeybee pollination resulted in higher numbers of pods and seeds than did self-pollination, the larger seed size in the lat- ter compensated the difference in yield weight. The shading decreased the number of pods, and the honeybee pollination resulted in the same amount of pods as did free access in the shaded plots. The number of seeds per pod was increased by the shading. The shelter against the sun and wind offered by the cage walls may have been favourable for the pol- linating insects. References Bengtsson, A. & Binoefors, S. 1975. Odlingstekniska försök med äkerböna. Inverkan av sätid, radavständ och utsädesmängd. Summary: Agronomic experi- ments with field beans. Effect of sowing date, row spacing and seed rate. Lantbr.högsk. Medd. A 229: 1—27. Bond, D.A. & Pope, M. 1974. Factors affecting the proportion of cross-bred and self-bred seed obtained from field bean (Vicia faba L.) crops. J. Agric. Sci. Camb. 83: 343—351. Clarke, H.E. 1970. The evaluation of the field bean (Vicia faba Linn.). Proc. Nutr. Soc. 29: 64—73. Free, J.B. 1966. The pollination requirements of broad beans and field beans. J. Agric. Sci. 66: 395—397. & Williams, I.H. 1977. The pollination of crops by bees. Apimondia. 14 p. Bucharest. Fyfe, J.L. 1954. Plant breeding studies in leguminous forage crops. 11. Further observations on natural cross-breeding in winter beans. J. Agric. Sci. Camb. 45: 141 147. Homola, I. 1973. The present stage of heterosis breeding in broad bean (Vicia faba L. var. equina). Genetika a Slechteni 9: 67 —74. Hovinen, S. 1988. Breeding of field bean (Vicia faba L.) with early maturity. J. Agric. Sci. Finl. 60: 260—267. Lawes, D.A. 1974. Field beans: improving yield and reliability. Span 17: 21 —23. McEven, J. 1973. The effects of growth regulators, seed rates and row spacings on field beans (Vicia faba L.). J. Agric. Sci. Camb. 80: 37—42. Poulsen, M.H. 1974. Pollination, seed setting, cross- fertilization and inbreeding in Vicia faba L. Zeitschr. Pfl.ziichtung 74: 97 —118. Scriven, W.A., Cooper, B.A. & Allen, H. 1961. Polli- nation of field beans. Outlook Agric. 3: 69—75. Varis, E., Hovinen, S., Kansanen, P. & Kauppila, R. 1982. Legumes in Finnish agriculture. Finnish Na- tional Fund for Research Development. Nitrogen pro- ject. Rep. 1. p. 219—231. Helsinki. Ms received August 21, 1989 48 SELOSTUS Mehiläisten merkitys härkäpavun pölyttäjinä Anna-Liisa Varis ja Raija Brax 1 Helsingin yliopisto. Maatalous- ja metsäeläintieteen laitos, 00710 Helsinki Helsingin yliopiston Viikin koetilalla järjestetyissä ko- keissa pyrittiin selvittämään, mikä merkitys hyönteispö- lytyksellä on härkäpavun sadonmuodostukseen sekä missä määrin mehiläisten suorittama pölytys vaikuttaa härkä- pavun satoon. Osalle koeruuduista asetettiin juuri ennen kukintaa hä- kit, joiden sisälle vietiin pieni mehiläisyhteiskunta, osal- le häkit, joissa pölyttäjähyönteisiä ei ollut. Lisäksi ko- keessa oli avoin koeruutu, johonpölyttäjähyönteiset pää- sivät vapaasti, sekä toisena koevuonna molemmista päis- tään avoin varjostushäkki. Koe järjestettiin vuosina 1979 ja 1980. Ensimmäisenä vuotena kasvu oli hyvä. Toisena vuotena kasvit tuleentuivat kuivuuden johdosta liian ai- kaisin ja sato jäi pieneksi. Mehiläispölytys lisäsi härkäpavun siemensatoa 19 % itsepölytykseen verrattuna, mutta ero ei ollut merkitsevä 95 %:n luotettavuudella. Sen sijaan avoin pölytys, jossa sekä mehiläiset että kimalaiset voivat vapaasti toimia pö- 1 Nykyinen osoite: Vaasankatu 14 B 32, 00500 Helsinki lyttäjinä, lisäsi satoamerkitsevästi pelkkään mehiläispö- lytykseen ja itsepölytykseen verrattuna. Siementen luku- määrä kasvia kohti oli sekä mehiläishäkkien että avoin- ten ruutujen kasveissa likimain kaksinkertainen verrat- tuina pölyttäjiltä suljettuihin häkkeihin ja myös siemen- ten lukumäärä palkoa kohti oli suurempi. Avoin pölytys vastasi lähinnä täydellistä pölytystä, koska härkäpapu- ala oli suhteellisen pieni ja pölyttäjien määrä riittävä. Kasvin korkeus, joka kuvastaa vegetatiivisen kehityksen nopeutta, oli ensimmäisenä vuotena suurin pölyttäjiltä eristetyssä häkissä osoittaen itsepölytykseen pakotetun kasvin pyrkimystä pitkittää vegetatiivista kasvua. Mehiläispölytyksellä saatu siementen suurempi luku- määrä osoittaa, että mehiläiset pystyvät Suomen olois- sakin pölyttämään härkäpavun kukan. Saadunkokemuk- sen perusteella mehiläisten käyttöä voi suositella laajoil- la härkäpapualoilla, joilla on puutetta kimalaisista. 49