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Suffolk Natural History, Vol. 53
AN INVESTIGATION INTO THE FORAGING RESOURCES OF THE SOLITARY BEE LASIOGLOSSUM SEXNOTATUM (KIRBY, 1802) (HYMENOPTERA: HALICTIDAE) ADRIAN KNOWLES Introduction The solitary bee Lasioglossum sexnotatum is one of the rarest British species, currently included within the National Red Data Book as “Endangered” (RDB1). Over the last 16 years, it has shown itself to be widely distributed in the far-south-east of the county and with a few records from the Brecks in the north-west. There are also recent records from the Norfolk section of the Brecks. In Suffolk, recent records come from suburban gardens and an allotment in Ipswich; the golf courses at Purdis Heath (Ipswich Golf Club) and Rushmere Heath; several of the parks around Ipswich; waste ground at Nacton; Martlesham Heath; gardens at Boyton and Felixstowe; Sudbourne, Holbrook Bay and a pub beer garden at Orford! Several environmental factors can limit the distribution of a species, including winter or summer temperatures, restricted forage diet or associations with other species. In order to examine whether or not foraging behaviour might in any way limit the species, a series of pollen samples were collected in the summer of 2017. These were sent to Dr Judith Webb, a ‘forensic ecologist’ in Oxfordshire who specialises in identifying pollen samples. Pollen identification is a specialised skill, relying on examination of the textured sculpturing of the grain casing. This delivers varying results, depending on the plant families/species involved. Some pollen is unique, allowing it to be assigned to a species with confidence. Other pollen sculpturing is shared amongst several species of a genus, whilst other types can only be assigned to a group of similar species. Methodology Pollen samples can be collected in two ways. Firstly, one can capture a pollen-laden female, place her in a small tube and leave her undisturbed in a cool, dark environment for a short while. Invariably, females comb off their pollen load and they can then be released to go about their business as usual, leaving the pollen sample in the tube. Secondly, pollen can be combed off pinned specimens in reference collections. Both methods were used in this small study, of eight different samples. Once delivered to Dr Webb, pollen was carefully brushed from the hairs on the pinned bees or brushed from the inside of tubes into a drop of water on a glass slide. A coverslip was placed on and gently compressed. The pollens were then viewed under x400 and x1000 (oil immersion) magnification, using a light microscope with the use of phase contrast illumination. Prepared pollen type slides and pollen from a dried flower reference collection were available for comparisons. Identification of fresh pollen is generally a lot harder than identification of prepared pollen that has been through chemical treatment to remove the cytoplasmic contents of each grain. Results Samples A-E come from localities in Ipswich. Sample A. Two sorts of pollen visible – about 50% of each. One was a Papaver (poppy) species, the other, larger grains from a Glaucium (poppy). Trans. Suffolk Nat. Soc. 53 (2017)
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Sample B. The majority (approximately 80%) of grains most likely from Salix (willow). The remainder were from Acer (maples). Sample C. Mostly the same pollens as for sample A (sample C was from the same location) i.e. Papaver and Glaucium poppies, plus a small number of a type of Rosaceae but not Prunus avium (Wild Cherry) or P. spinosa (Blackthorn). These could easily be Sorbus/Rosa/Rubus. Sample D. The same type of Rosaceae pollen as Sample C (but different locality). Not Prunus avium (Wild Cherry) or P. spinosa (Blackthorn). These could easily be Sorbus/ Rosa/Rubus. Sample E. All Asteraceae ‘Fenestrate’. Many genera have this type: Taraxacum, Crepis, Hieracium, Hypochoeris, Lapsana, Leontodon, Tragopogon, Sonchus, Mycelis). The bees have been observed foraging at Common Cat’s-ear (Hypochaeris radicata) at this locality, so this is probably the source of much of this pollen type. Sample F. From Boyton. All Senecio-type (many genera have this type,:Senecio, Bellis, Bidens, Aster, Conyza, Calendula, Erigeron, Petasites, Inula, Rudbeckia, Solidago). The garden is known to support a shrubby Senecio plant, which is likely to be the source of this sample. Sample G. From Nacton Heath. All a type of largish pollen that resembles some members of the Scrophulariaceae, but not any of the wild species previously examined, like foxglove, figwort, mullein and toadflax. Most resembles a garden Penstemon. I collected this bee from waste ground but next to some ornamental planting on the edge of an industrial estate, while I was waiting for my car to be MoT tested! The same garage may be getting my custom in 2018, so I can try and pin down likely contenders. Sample H. Minsmere. Two sorts of grains, roughly 50:50 Rhamnus (buckthorn) and something from the Rosaceae that is not Prunus – could be Rosa/Rubus/Cotoneaster/ Pyracantha but cannot be definitively identified. This sample was taken from the environs of the car park at the Minsmere RSPB visitor centre, so several ornamental species plus native plants might account for the Rosaceae pollen. The female was taken from buckthorn flowers, where she was evidently nectaring, but this confirms that pollen was also being collected from this bush. Conclusions The larvae of Lasioglossum sexnotatum are not fussy eaters! Although the sample size is quite small, the pollens observed come from trees and shrubs (willow, maple and buckthorn), shrubby rose family plants, yellow daisy family plants (two different groups) and poppies (two different genera). Thus, diet is clearly not a limiting factor in the current UK distribution of this species. The investigation goes on... Acknowledgement The pollen analysis work has been funded by a Morley Bursary from the Suffolk Naturalists’ Society. The author is grateful for this financial assistance, which has helped further our knowledge of the ecology of this species in Britain. Adrian Knowles, Jessups Cottage, London Road, Capel St Mary, IP9 2JR
Trans. Suffolk Nat. Soc. 53 (2017)