Proceedings of the 37 th International Apicultural Congress, 28 October – 1 November 2001, Durban, South Africa APIMONDIA 2001 To be referenced as: Proc. 37 th Int. Apic. Congr., 28 Oct – 1 Nov 2001, Durban, South Africa ISBN: 0-620-27768-8 Produced by: Document Transformation Technologies Organised by: Conference Planners PEAR POLLEN DIGESTION BY LARVAE OF OSMIA CORNUTA LATREILLE (HYMENOPTERA MEGACHILIDAE) Laura Cresti 1 , Massimo Nepi 1 , Bettina Maccagnani 2 , Edith Ladurner 2 , Ettore Pacini 1 1 Dipartimento di Scienze Ambientali, Università degli Studi di Siena, Siena (Italia) 2 Dipartimento di Scienze e Tecnologie Ambientali, Università degli Studi di Bologna, Bologna (Italia) Abstract Histochemical study of Pyrus communis pollen modifications in bee provisions and in the alimentary canal of 4 th and 5 th instar larvae of Osmia cornuta was performed. Modifications were already evident in the provisions and consisted of cytoplasm protrusion through apertures and changes in carbohydrate content (increase in glucose and fructose and decrease in sucrose and starch). When pollen was ingested by the larvae, the pollen protoplast underwent to plasmolysis, i.e. it retracted from the pollen wall. Digestion of pollen began in the fore ventriculus where we observed: 1) disorganised intine at the apertures; 2) disappearance of nuclear DNA; 3) fewer pollen grains containing starch compared with provisions; 4) some empty pollen grains. Pollen was observed in the proctodeum only in the 5 th instar larvae, where it appeared extremely compressed and crushed. Pollen grains containing starch alone (probably dead pollen grains) were only slightly deformed. Key words: Osmia cornuta, bee pollen provisions, pollen digestion, starch, proteins. Introduction Specialised monocultures in the field and cultivation in protected environments have led to a sharp rise in the demand for pollinating insects. At the same time, Italian honey bee population has been decimated by a variety of pathogens (varroasis, American foulbrood and myasis). Research has therefore been begun into the rearing of wild Apoidea for controlled pollination. Results on Osmia spp. suggest that this bee could be useful for pollination (Bosch and Blas, 1994; Felicioli, 2000). Pedotrophic nests of insects of the genus Osmia consist of a linear series of cells, each containing a provision of pollen. One egg is laid on the pollen provision in each cell. After a few days a small