Introducing plants for bee-keeping at any cost? – Assessment of Phacelia tanacetifolia as nectar source plant under xeric Mediterranean conditions

Abstract.

 We assessed nectar and honey potential of Phacelia tanacetifolia, an American plant, under Mediterranean conditions. Its flowering occurred during the major flowering season unless intensely irrigated, whereas duration and flower life span were shorter compared to continental conditions. Mediterranean climate limitations to nectar secretion were assessed on plants grown under natural conditions (xeric) vs. regular irrigation. May flowering xeric plants produced less nectar per flower than the irrigated ones, but had the same nectar potential per surface area. On the contrary, at the cost of intense irrigation, July flowering plants produced much higher nectar per flower and per surface area compared to xeric ones. In all flowering periods and sections honeybees were the most constant and numerous visitors, visiting the flowers mainly for nectar, whereas solitary bees were scarce. Based on our results, we suggest that although the plant may be a good nectar source for honeybees in some cases, we have serious reservations for a generalised use in the Mediterranean.