BIOLOGY AND POPULATION-STRUCTURE OF OSMIA-TRICORNIS LATREILLE (HYM, MEGACHILIDAE)

Osmia tricornis Latreille is a univoltine species that in NE Spain fli es from April to June. In 1990 and 1991 two populations were reared in the laboratory. Bees were incubated at 25-30-degrees-C during the sum mer and overwintered in refrigerators at 3-7-degrees-C for 112 and 167 days respectively. In spring bees were released in the field and prov ided with nesting materials with holes of different diameters. Bees th at had been exposed to longer over-wintering periods emerged sooner an d expressed lower over-wintering mortality than bees exposed to shorte r over-wintering periods. Females preferred to nest in holes of 7 mm i .d. The nesting season lasted from 2 to 2,5 montes. 0. tricornis is a highly polylectic species and collected pollen mainly from flowers pro ducing little or no nectar (Quercus, Cistus, Papaver, Ranunculus, etc. ). Several parasites and predators were found in the nests: Chaetodact ylus osmiae (Dujardin), Monodontomerus obsoletus Fabricius, Anthrax an thrax Schrank, Trichodes alvearius Fabricius, Melittobia sp. Westwood, Cacoxenus sp. Loew, Sapyga quinquepunctata (Fabricius), Stelis phaeop tera (Kirby) and Ptinus sexpunctatus Panzer. In both years, population s obtained at the end of the flying season were larger than population s initially released. 0. tricornis showed very similar biological feat ures to those of other Osmia (s. str.) Panzer species currently being used as crop pollinators.