The effect of pollen protein concentration on body size in the sweat bee Lasioglossum zephyrum (Hymenoptera : Apiformes)

Adult bees and wasps provide all the food their offspring require to grow from egg to adult. For a given diet. offspring body size generally increases with an increase in the amount of food consumed as a larva, but the extent to which body size is influenced by the type of food consumed is poorly known. Pollen ranges from 2-60% protein among plant species, and bees are extremely efficient at assimilating nitrogen; therefore, it seems likely that either parent bees adjust the size of larval provisions to compensate for differences in pollen protein concentration or bee offspring attain different body size depending on the pollen type(s) consumed as a larva, We presented the generalist sweat bee Lasioglossum zephyrum with pollen diets that differed in protein content and monitored offspring body size during two experiments. In a protein supplementation experiment, diets ranged from 20-66% protein and consisted of Typha pollen amended with soy protein. On a pollen/soy diet, offspring body size increased 25% with a shift from 20-37% protein, but did not increase further at greater protein concentrations, In a multiple pollen experiment, pollen diets ranged from 20-39% protein and consisted of eight pollens that differed naturally in protein concentration. The largest offspring arose from the most protein-rich pollens, whereas much smaller bees developed on protein-poor pollens, Provision size only predicted offspring size when pollen type, and therefore protein quantity, was considered. Adult foragers did not adjust provision size to compensate for pollen protein, Therefore, offspring body size appears to result from a combination of controlled (provision size) and uncontrolled (pollen quality) factors that arise out of bee foraging decisions