J. Insect Physiol. Vol. 43, No. 1, pp. 89–100, 1997  1997 Elsevier Science Ltd Pergamon Printed in Great Britain. All rights reserved 0022-1910/97 $17.00 + 0.00 S0022-1910(96)00024-8 Digestion of Pollen Components by Larvae of the Flower-Specialist Bee Chelostoma florisomne (Hymenoptera: Megachilidae) HEIDI E. M. DOBSON,*† YING-SHIN PENG* Received 13 October 1995; revised 29 December 1995 Pollen digestion in larvae of the solitary bee Chelostoma florisomne (Megachilidae), a pollen- specialist (oligolectic) species on Ranunculus spp. (Ranunculaceae), was investigated using histological techniques. Serial sections from the anterior-, median-, and posterior- midgut/hindgut regions of the larval alimentary canal were selectively stained and examined for disappearance of lipids, proteins, and carbohydrates from ingested Ranunculus pollen grains. During digestion, pollen contents were observed to gradually extrude through the grain apertures. Most of the digestion of lipids and proteins occurred in the anterior- and median- midgut, whereas carbohydrates disappeared more slowly and mainly in the median- and pos- terior-midgut. In the hindgut, pollen comprised mainly empty exine shells, which were crushed and often broken, suggesting that some components of the wall are degraded during digestion, causing collapse of the outer, chemically resistant wall layer (exine). Lipids were completely digested, but small quantities of proteins and carbohydrates were often still present in grains in the posterior midgut/hindgut. The pollenkitt appeared to be completely absorbed, with none evident in the posterior midgut or in larval feces. The findings indicate that this oligolectic bee has the digestive equipment necessary to effectively remove and absorb the nutrients present in the pollen of its restricted food source. Comparison with similar studies in adult honey bees suggests that differing digestive abilities might be an underlying factor in pollen speciali- zation in bees.  1997 Elsevier Science Ltd. All rights reserved Histology Ranunculus spp. Nutrition Oligolecty INTRODUCTION survival or reproduction (e.g. oogenesis). It has been documented in numerous orders, including Collembola Pollen is used as food by a diversity of flower-feeding (Scott and Stojanovich, 1963; Kevan and Kevan, 1970), animals, providing nutrition through its rich content of Orthoptera (Lockwood and Bomar, 1992), Thysanoptera proteins, lipids, carbohydrates, as well as vitamins and (Grinfel’d, 1959; Kirk, 1984), Diptera (Wilson and minerals (Todd and Bretherick, 1942; Stanley and Lin- Lieux, 1972; Holloway, 1976; Gilbert, 1981; Leereveld, skens, 1974). Pollen-feeders include vertebrates, such as 1982; Ssymank and Gilbert, 1993; Nicolson, 1994), birds (Churchill and Christensen, 1970; Cox, 1984; Brice Coleoptera (Siegfried and Mullin, 1990; Rickson et al., et al., 1989), bats (Howell, 1974; Cox, 1984; Law, 1992), 1990; Benedict et al., 1991; Nalepa et al., 1992), Lepi- and marsupials (Turner, 1984; Smith and Green, 1987; doptera (Gilbert, 1972; Rogers, 1978), and Hymenoptera, Goldingay, 1990), but most abundant are the invert- in both wasps (Hunt et al., 1991) and most particularly ebrates, especially mites (Royce and Krantz, 1989; Ouy- bees (Roubik, 1989). As a group, bees depend strongly ang et al., 1992) and insects (Stanley and Linskens, 1974; on pollen for their sustenance, obtaining from it all their Faegri and van der Pijl, 1979). The eating of pollen required proteins together with lipids and other nutrients. occurs widely in insects, many of which require it for In the case of honey bees and stingless bees, pollen-feed- ing occurs mainly in the adult stage, where it stimulates the production of glandular secretions that are fed to the *Department of Entomology, University of California, Davis, CA larvae (Haydak, 1970). However, in most bee species, 95616, U.S.A. including all solitary bees, pollen forms the principal †Author for correspondence. Current address: Department of Biology, Whitman College, Walla, Walla, WA 99362, U.S.A. food of the larvae while the adults eat it to only varying 89