Recent work questions the nutritional quality of many types of pollen  
sources that bees commonly use for food

SPECIALIZED BEES FAIL TO DEVELOP ON NON-HOST POLLEN: DO PLANTS  
CHEMICALLY PROTECT THEIR POLLEN?
CHRISTOPHE J. PRAZ, ANDREAS MULLER AND SILVIA DORN
Ecology, 89(3), 2008, pp. 795–804

Abstract. Bees require large amounts of pollen for their own  
reproduction. While several morphological flower traits are known to  
have evolved to protect plants against excessive pollen harvesting by  
bees, little is known on how selection to minimize pollen loss acts on  
the chemical composition of pollen. In this study, we traced the  
larval development of four solitary bee species, each specialized on a  
different pollen source, when reared on non-host pollen by  
transferring unhatched eggs of one species onto the pollen provisions  
of another species. Pollen diets of Asteraceae and Ranunculus  
(Ranunculaceae) proved to be inadequate for all bee species tested  
except those specialized on these plants. Further, pollen of Sinapis  
(Brassicaceae) and Echium (Boraginaceae) failed to support larval  
development in one bee species specialized on Campanula  
(Campanulaceae). Our results strongly suggest that pollen of these  
four taxonomic groups possess protective properties that hamper  
digestion and thus challenge the general view of pollen as an easy-to- 
use protein source for flower visitors.

* * *

Pollen of Asteraceae was shown to be of poor quality for the honey  
bee, for bumblebees as well as for two solitary bee species. Many  
members of Asteraceae are copious nectar producers. Centaurea  
(knapweed), Helianthus annuus (domestic sunflower), and some species  
of Solidago (goldenrod) are major "honey plants". Some members of the  
Asteraceae are economically important as weeds. Notably in the United  
States are the ragwort (Senecio jacobaea), groundsel (Senecio  
vulgaris), and Taraxacum (dandelion).

Peter Loring Borst
Ithaca, NY  USA
+42.347999, -76.495239

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html

Access BEE-L directly at:
http://community.lsoft.com/scripts/wa-LSOFTDONATIONS.exe?A0=BEE-L