, 3rd Syrphidae Symposium Presentation given at the nd to 5th September, 2005 Leiden, The Netherlands, 2

Pollen supply and feeding The role of pollen in a syrphid’s preferences of syrphids in metabolism shrub/herb vegetation boundary by • Maturing of sex organs feces analysis • Protein supply for basic metabolism • Exine of the pollen is indigestible Wilfried H.O. Ernst • Digestion of the interior of the pollen Hoofddorp grain only after pollen germination in the gut and enzymatic break-down of the intine

• Methods Scope of feces analysis • (1) Analysis of pollen types in feces hand-collected syrphids kept in plastic bottles with transparent walls up to • Diurnal diversity of flower visits by the defecation. same individuum • At feces removal, measurement of the size of the feces • Dispersal and homogenization of feces in water on • Seasonal diversity of flower visits by the microscope slides. same • Microscopic analysis of three-time 100 pollen grains using a • Differential exploitation of flowers by grid of 73 or 29 µm (Golding & Edmunds, 2003) syrphid species in a small geographic area • (2) Feeding experiment • Keeping syrphids for three hours for defecation. Then • Time for pollen passage through the gut addition of inflorescences with morphologically contrasting • Efficiency of pollen digestion pollen types for one hour. Each feces was removed immediately and analyzed. • (3) Pollen digestion (Haslett, 1983) as % ingested pollen

Species-specific opening and closing time of flowers Feces size and form Flowers of Lapsana communis (blue) open and close Surfaces vary from 0.070 mm² in small earlier than those of Cichorium intybus (red) and Crepis species (Melanostoma) up to 16 to 20 mm² in biennis (yellow). Consequence for syrphids: switching large species (Volucella zonaria). to other food sources during a day. Forms are round, worm-like and patches. Daily flowering period From left to right feces of: Syrphus ribesii, Episyrphus 120 balteatus with pollen of Chenopodium album, 100 Episyrphus balteatus with pollen of Ligustrum vulgare, 80 Melanostoma scalare, scripta 60

flowers 40 20

open of Percentage 0

:40 :30 30 8:00 8 9:30 4: 11 13:00 1 17:00 Time (+2 h GMT) , 3rd Syrphidae Symposium Presentation given at the nd to 5th September, 2005 Leiden, The Netherlands, 2 1 , 3rd Syrphidae Symposium Presentation given at the nd to 5th September, 2005 Leiden, The Netherlands, 2

• Residence time of pollen in Episyrphus balteatus Open and closed flowers of When collected from inflorescences of the syrphids had consumed pollen of Plantago Cichorium intybus lanceolata (red) and Heracleum sphondylium (yellow) which stopped after sampling. Between 110 to 180 min flowers of Rubus fruticosus (blue) were offered for pollen consumption. Residence time of pollen can be more than 6 hours. Pollen excretion

100% 80% 60%

pollen 40% 20% total of Percentage 0% 40 60 120 150 180 240 280 300 340 Time after finishing feeding (min)

• Relationship between feces size and the Species-specific pollen consumption number of pollen grains per feces in the same environment There is a highly significant correlation •Only Epistrophe eligans and Neoscia podagrica (P<0.001): y (number)=1300+0.72 x (surface) ingested pollen of the tree Prunus avium, all other syrphids took pollen from herbs Feces size and pollen amount • Bras- Tussi- Tara- Bellis Prunus • sica lago xacum avium 25000 20000 • Ch. pagana 87 0 13 0 0 15000 10000 • E. arbustorum 0 100 0 0 0

per feces per 5000 0 • E. lineata 66 0 31 3 0 number of pollen pollen of number 0 5000 10000 15000 20000 25000 • H.pendulus 0 85 14 1 0 Projected surface of feces (um2) • N. podagrica 0 0 0 0 100 • E. eligans 0 0 0 0 100

Digestion of Plantago lanceolata by • Not all pollen types found in feces of the syrphids were the Episyrphe balteatus result of visits to different plant species, but were due to contamination of inflorescences by wind-dispersed or -transported pollen. Six inflorescences of Cichorium • Only less than 30% of the ingested pollen of intybus were sampled just at closing time (noon) and per Plantago lanceolata is digested during six hours inflorescence 10 stigmata were pooled to one sample and after ingestion. counted for 50 pollen of the host plant (blue). Contamination of inflorescences Digestion of pollen of Plantago 100% 30.00 80% 60% 20.00 40% 20% 10.00 pollen number number pollen 0% Percentage of total Percentage of

digested pollen 0.00 123456 100 120 180 210 240 300 340 360 Inflorescence Time (min) after ingestion , 3rd Syrphidae Symposium Presentation given at the nd to 5th September, 2005 Leiden, The Netherlands, 2 2 , 3rd Syrphidae Symposium Presentation given at the nd to 5th September, 2005 Leiden, The Netherlands, 2

Conclusion • During the day, species taking pollen from flowers with a daily opening and closing rhythm have to move to other pollen suppliers. • During the season, pollen of a high diversity of plant species are used without specific preferences. • Not all pollen ingested are digested. • Due to contamination of inflorescence by foreign pollen, low percentage of pollen types in feces do not indicate visit of syrphids to different plant species.

, 3rd Syrphidae Symposium Presentation given at the nd to 5th September, 2005 Leiden, The Netherlands, 2 3