Factors affecting offspring body size in the solitary bee Osmia bicornis (Hymenoptera, Megachilidae)

Body size is related to fitness in many insects. In solitary bees offspring body size is largely determined by maternal provisions and microclimate. We studied the effect of quantity and quality of provisions and rearing temperatures (20, 25 and 30 °C) on body size in the Red Mason bee, Osmia bicornis. Cocoon weight increased with provision weight and decreased with increasing temperature. High temperature (30 °C) led to high mortality of larvae and smaller body size, partly due to incomplete consumption of the provisions. Diversity of pollen in the provisions was low, and most provisions primarily consisted of mainly oak and maple pollen. Pollen diversity did not affect cocoon weight and males provided with pure oak or pure maple pollen showed similar adult size. Our results suggest that the quantity of provisions and temperature, but not pollen quality influence the development of O. bicornis progeny and might affect population dynamics of this abundant European pollinator.