EVALUATING HONEY-BEES AS POLLINATORS OF VIRGIN FLOWERS OF ECHIUM-PLANTAGINEUM L (BORAGINACEAE) BY POLLEN-TUBE FLUORESCENCE

A novel technique was developed which simply, directly and quantitativ ely evaluated flower visitors as pollinators of Echium plantagineum in Canberra, Australia, based on microscopic detection of the fluorescen ce of the callose content of stylar pollen tubes stained with aniline blue. E. plantagineum is self-compatible, so that germination and poll en tube growth of both cross- and self-pollen to the ovules at the sty le base occur. The technique utilized 'virgin' flowers, bagged as buds and which subsequently opened within the bags. After careful unbaggin g, the majority (93.5%) of initial visitors to these previously-unvisi ted flowers were honey bees (Apis mellifera). The technique demonstrat ed that although autogamy was possible, it was not predominant in E. p lantagineum because permanently-bagged flowers had very low numbers of pollen tubes at their style bases (usually none), and emasculated and intact flowers exposed to single honey bee visits usually had the sam e numbers of tubes. Within treatments (intact, emasculated), honey bee visits for pollen, nectar or both, did not result in differences in p ollen tube number, nor was there any connection between degree of poll ination and time spent by a single honey bee per virgin flower. Althou gh most honey bees attending virgin flowers carried pellets of E. plan tagineum pollen on their hind legs, as a result of grooming actions to gather grains from their bodies, they were still as effective as poll inating agents as bees lacking corbicular pollen. Because one-third of single honey bee visits to emasculated virgin flowers (bearing recept ive stigmas) introduced sufficient pollen to achieve fertilization of all four ovules, and almost two-thirds of such visits resulted in poll ination, it appears that honey bees were effective cross-pollinators o f E. plantagineum. Various advantages of the technique, including appl ications to agriculture, are discussed.