AN ULTRASTRUCTURAL-STUDY OF POLLEN GRAINS CONSUMED BY LARVAE OF OSMIABEES (HYMENOPTERA, MEGACHILIDAE)

Pollen samples from provisions and faeces found in the nests of four O smia species were analyzed by SEM and TEM. The pollen grains studied w ere Cistus, Sonchus type oleraceus, Prunus type dulcis, and Quercus ty pe ilex. The apertures of Cistus and Sonchus pollen stored in the prov isions were slightly expanded, and the cytoplasm protruded through the m. Conversely, Prunus and Quercus pollen grains showed hardly any sign s of such apertural protrusions. Further, the cytoplasm of Cistus and Sonchus pollen (which have thin intines) was almost entirely lacking i n the pollen grains recovered from faeces, while in the faecal pollen grains of Prunus and Quercus (with thick intines) the cytoplasm was mu ch less modified. These preliminary results indicate that both the pro trusion of the cytoplasm in the provisions and the thickness of the in tine may play an important role in the digestion of pollen grains by O smia bee larvae.