Phenology of the specialist bee Colletes hederae and its dependence on Hedera helix L. in comparison to a generalist, Apis mellifera

Colletes hederae,the ivy bee, (Hymenoptera: Colletidae) has undergone large range expansions in Europe in recent years, including colonising Britain in 2001 with its original distribution limited to Western mainland Europe and the Channel Islands. It is thought to specialise onHedera helixL. (Apiales: Ariliaceae), common ivy. However, some research has questioned this dependence. This study quantifies the foraging ecology ofC. hederaeto determine its relationship with ivy in Sussex. We quantified the phenology of ivy bloom,C. hederaeactivity and flower visitation, and pollen collection of females through pollen analysis. We also gathered equivalent data onApis melliferaboth as a comparison and to assess alternative pollen sources. The phenology of femaleC. hederaeactivity was highly correlated with and phonologically contained within the ivy bloom period. Pollen analysis fromC. hederaeidentified ivy pollen was 98.5% of samples, significantly more than forA. mellifera(90%). Two other plant species were identified and more common inC. hederaesamples when ivy bloom was not at its peak. Surveys of ivy flowers surrounding the aggregations found thatC. hederaewere the most common insect (26%) foraging on ivy.AlthoughC. hederaecan forage on other species, ivy was found to be an important floral resource. The results also suggest the potential for competition withA. mellifera, the only other bee present in more than small numbers onH. helixflowers, as althoughA. melliferais a generalist, in autumn it mainly forages on ivy.

Floral vibrations by buzz-pollinating bees achieve higher frequency, velocity and acceleration than flight and defence vibrations

Vibrations play an important role in insect behaviour. In bees, vibrations are used in a variety of contexts including communication, as a warning signal to deter predators and during pollen foraging. However, little is known about how the biomechanical properties of bee vibrations vary across multiple behaviours within a species. In this study, we compared the properties of vibrations produced by Bombus terrestris audax (Hymenoptera: Apidae) workers in three contexts: during flight, during defensive buzzing, and in floral vibrations produced during pollen foraging on two buzz-pollinated plants (Solanum, Solanaceae). Using laser vibrometry, we were able to obtain contactless measures of both the frequency and amplitude of the thoracic vibrations of bees across the three behaviours. Despite all three types of vibrations being produced by the same power flight muscles, we found clear differences in the mechanical properties of the vibrations produced in different contexts. Both floral and defensive buzzes had higher frequency and amplitude velocity, acceleration, and displacement than the vibrations produced during flight. Floral vibrations had the highest frequency, amplitude velocity and acceleration of all the behaviours studied. Vibration amplitude, and in particular acceleration, of floral vibrations has been suggested as the key property for removing pollen from buzz-pollinated anthers. By increasing frequency and amplitude velocity and acceleration of their vibrations during vibratory pollen collection, foraging bees may be able to maximise pollen removal from flowers, although their foraging decisions are likely to be influenced by the presumably high cost of producing floral vibrations.