Acta Neerl. 28 177-195 Bot. (2/3), May 1979, p. Effects of bumblebee visits on the seed set of Pedicularis, Rhinanthus and Melampyrum (Scrophulariaceae) in the Netherlands Manja+M. Kwak Laboratorium voor Plantenoecologie,Biologisch Centr-um, Rijksuniversiteit Groningen, SUMMARY Thepollinationecology offive species ofRhinanthoideae (theannual species Rhinanthus serotinus, R. minor and Melampyrumpratense, the biennial Pedicularis sylvatica and the annual and biennial P. palustris) has been investigated. All species contain pollen and nectar and arefrequentlyvisited by sternotribically and nototribically pollinating bumblebees. The effectiveness of pollen transfer has been measured by the use of fluorescent and differences exist in of fluorescent powder. In R. serotinus M.pratense no percentages R. stigmas of flowers nototribically or sternotribically visited by bumblebees. minor flowers, visited sternotribically, have very low percentages of fluorescent stigmas. This indicates that the pollen- covered venter cannot touch stigmas enclosed by the galea; the movements of the bumblebees caused P. R. and M. flowers probably self-pollination, palustris, serotinus pratense are very frequently bumblebees. perforatedby nectar-collectingshort-tongued P. sylvatica and R. minorflowers are very rarely perforated.On these species nectar is mainlycollected by nototribicallypollinatingbumblebees. Seed productionand dependenceuponpollinationby bumblebees (Bombus Latr. spp.) areconsidered. A range from highdependenceuponbumblebee visits for seed production in P. palustris,tomedium dependencein P. sylvatica and R. serotinus and virtual independencein R. minor and M. pratense is established. No species is completely self-sterile. Seed set in caged plants is due to favourable morphology and position offlowers. Close proximity ofthecae and stigmaor a downward curving of the pistil under pollen chamber in Melampyrum and Rhinanthus insure seed set in caged plants. In Pedicularis these characteristics for self-pollination are absent. The importance of bumblebees for the five Rhinanthoideae and the reciprocal importance of these pollen and nectar providing plants for bumblebees is discussed. The importance of alternative pollination by honeybees, thrips and wind is evaluated. 1. INTRODUCTION The of extend present study was undertaken, as part a general survey, to our knowledge of the floral ecology of Rhinanthoideaeby detailed analysis of polli- nator behaviour in its general ecological context. The pollination mechanisms have been described in a previous paper(Kwak 1977). Thezygomorphic, nectari- ferous visited bumblebees flowers are mainly by (Bombus Latr. spp.), nototribi- cally and sternotribically. This deals with the ofbumblebeevisits for the seed setof five paper significance hemiparasites in the northern Netherlands: Pedicularispalustris L., P. sylvatica L., Rhinanthusserotinus(Schonh.) Oborny (= R. angustifolius Gmelin), R. minor L. These annual biennial.In the L., Meiampyrum pratense species are or addition, 178 M. M. KWAK importance of alternative pollination by honeybees, thrips and wind, will be evaluated. Honey bees, collecting pollen and nectar on alpine Rhinanthus species, are mentionedby Fossel (1974). Theirpollination efficiency is unknown. five In the literature the ability to self-pollinate in the species depends on the view of the authors. Several mechanisms of selfing are described: the close the that the is proximity ofanthers and stigma, the curving of style so stigma under the ofthe with the anthers attheendof the flowering period, and decrease pressure which the pollen chamber is kept closed at the end of the flowering period (Muller 1881; Knuth 1899; Wagner 1908; Warming 1908; Heukels 1910; Von Kirchner 1911; Schoenigem 1922; Kerner von Marilaun 1902;Werth of 1940; Lagerberg et al. 1957; Faegri & van der Pul 1966). The presence hairs on the thecae is mentionedinrelation to the ability ofself-pollination and of the prevention of lateral pollen release during bumblebee visits (Knuth 1899; Schoenigem No available of Heukels 1910; 1922). comparative figures are crossing and selfing. In this context the remark by Smith(1963) thatMelampyrum pratense had a good seed set in the greenhouse, probably in absence of bum- blebees, is most pertinent. Other Melampyrum species also exhibit autogamy (Cantlon et al. 1963; Hartl 1974). Alpine RhinanthusandPedicularis species are able to self-pollinate, according to Muller (1.c.) and Knuth (1.c.). Self- pollination in buds of R. minor in the Faroes is mentionedby Hagerup (1951). in America few when Pedicularis species produced very or no seeds caged (Sprague 1962; Macior 1970, 1973, 1974, 1975, 1977). Maclnnes (1972) men- tions arctic Pedicularis populations consisting ofplants which self-pollinate and are self-fertile and plants which neither self-pollinate nor are self-fertile. 2. METHODS AND MATERIALS Field studies conducted from until October in in were May 1974-1978 popu- lationsof Pedicularis palustris, P. sylvatica, Rhinanthus serotinus, R. minorand Melampyrum pratense in the northern Netherlands including the West Frisian island of Schiermonnikoog. A R. minorpopulation in the southern Netherlands was also visited. Self-pollination potentials for each species were determinedby comparing fruit development on plants caged to exclude pollinating insects with fruit development on uncaged plants in the immediatevicinity of the caged ones. Lace covered (meshes 1 x 1 mm) cages 60 x 60 x 60 cm were placed over whole individual for insect plants, or bags were placed over stems. Except M. pratense, exclosures were used both in the fieldand in the experimental garden. One ofthe R. minorpopulations, grownin theexperimental garden, was ofFrench origin; seeds had been collected in a dune population near Portbail (Normandy). To analyze the possibility ofautodeposition ofpollen or self-sterility, stigmas of of and in fromthe caged flowers P. palustris P. sylvatica were dipped ripe pollen same flower. The effectiveness of pollen transfer by bumblebees was studied by sites with touching the pollen on the bodies of the visiting bumblebees a brush containing afluorescentpowder (“Daylight” Fluorescent Heffnerand Co.)These 179 POLLINATION ECOLOGY OFFIVE HEMIPARASITIC RHINANTHOIDEAE II bumblebeescontinuedtheirforaging trips. Visited flowers were collected and the styles removed and examined with a UV lamp for the presence of fluorescent powder. Pollen germination and pollen tube growth were observed by UV fluorescence microscopy (Linskens & Esser 1957; Martin 1959) using a 2% solution of water-soluble aniline blue in K P0 dye 20% 3 4 (Wilms 1974). The possibility ofhoneybee pollination was examined. Two hives were placed at the edge of a dense stand of Rhinanthus. Pollen loads were collected by using a pollen trap and examined by light microscopy. Hives were also present at a distance of about 30 m from the experimental garden. The ofwind of in dense standof possibility dispersal pollen was examined a very conditions flowering R. serotinus when weather were favourable. Test slides, coated with silicon oil on one side to catch air-bornepollen grains, were placed at different levels above the ground: 15, 25, 35, 45 and 55 cm, with the coated side wind. slides leftfor facing the Test were 12 hours, from 23.00 till 11.00hours and from 11.00 till 23.00 hours. They were examined microscopically for Rhinanthus pollen. Fig. 1. Flowers of the five plant species studied in natural positions, under insect-exclosures: A = N S = O = = anthers; stigma; ovary; nectary. a. P. palustris; b. P. sylvatica; c. R. serotinus; d. R. minor; e. M. pratense. 180 M. M. KWAK number seeds/caps. observed 4 4 max, 3838 25 3434 18 18 antheranther first ripe short shortshort long long long on hairs thecae absent absentabsent present present present stigma protr. protr.protr. protr. end. end. mm 9-20 7-10 9-11 tube lengthlength 9-20 7-10 14-17 7-9 10-13 in mm corolla length 17-2017-20 15-18 20-24 17-22 13-17 13-16 in Melampyrum. color purplish/pinkpurplish/pink tooth) flower pink yellow (bluetooth)(bluetooth) yellow/ (white yellow/white and pink Rhinanthus September JulyJuly j J Augustus-September May-September Pedicularis, flowering-time May— Augustus May-July May-July June-July of {j||\|2 characteristics form biennial biennial life biennial annual biennial annual annual annualannual Selected 1. palustris sylvatica serotinus minor pratense Table P. P.P. R. R. M. POLLINATION ECOLOGY OF FIVE HEMIPARASITIC RHINANTHOIDEAE II 181 : + plant + + 86.886,8 96.096,0 87.5 86.7 80.0 — 85.7 - 97.5 37.3 20.0 0 75.0 83.3 80.880.8 42.9 these 0 % sterno- tribic 100 100 1977; V/ on 1974- mber foraging number loads 5 — 6 - — 4 7 - of ™ of loads 36 38 75 16 15 21 40 18 59 1010 24 2626 + ) ) jonellus B. + + (+)+ + + observation bumblebees ( ( +++ +( + + + + + + + + + on lucorum B.B. from + + + + + + + + + + + + + + + + + terrestris/ B. ++ ++ +++ +++ +++ +++ ++ ++ based + + + + + + + + + + + + + + + + + + + + 1974 part in first taken hypnorum B. + + + + + + + + ; ++++ + + + + loads, pratorum B. + +++ + + + + + +++ + + + + + + + + Melampyrum pollen +++++ + + ) of ++ lapidarius B. + + + + + + + + + + + + tand (( amount ruderarius B. + + Rhinanthus on based ) equestrisequestris B. (+) (+)(+> (+> (+)+ ( Pedicularis, part of second muscorum + + + + + B. + + + + + + + + + + rare; ++++ + + + ++ + + + + + + + + populations pascuorum + + + + + + + + + +++ +++ + + + + + + + + + + (+): B. + +++ + on + ++++(+) +++ + ++ +++ +++ species occasional; hortorum B. + + + + + +