Floral Visitors to Chinese Date (Ziziphus jujuba) in New Mexico and Their Potential Role in Pollination

Chinese date or jujube (Ziziphus jujuba Miller) is a drought-tolerant fruit tree that grows well in the southwestern U.S. Its small flowers produce copious nectar in ring-shaped nectaries that are readily accessible to a wide range of insects. In China, where the species originated, it is pollinated mainly by the Asian honeybee (Apis cerana), which is absent from the U.S.A. Here, domesticated European honeybees (Apis mellifera) are not strongly attracted to jujube flowers, and the principal pollinators are unknown. In order to investigate the role of various potential pollen vectors, three studies were conducted at two sites in New Mexico (Los Lunas and Alcalde) from 2012-13. Preliminary collections of insect visitors to jujube flowers were made at both sites in 2012 and the pollen load on each insect was determined by collecting the pollen with a glycerin gel containing basic fuchsin; microscope slides were prepared from these samples and the pollen grains counted under 100x magnification. In 2013, timed collections of floral visitors were made throughout the day on two separate days at each site and the pollen load analysis repeated as above. In addition, an exclusion study was conducted at Los Lunas to determine the relative importance of nocturnal insects (e.g. night-flying moths) versus diurnal insects as pollinators, and to calculate the pollination efficiency of individual (diurnal) insects by capturing the first insect to visit a previously bagged flower and measuring the pollen load on both the insect and floral stigma after the visit. Our results indicate that diurnal insects are more effective pollinators than are nocturnal visitors and that a wide range of insects are capable of effecting pollination. Predatory wasps (both solitary and social species) from five families (Sphecidae, Pompilidae, Vespidae, Cabronidae, and Thynnidae) were the dominant insect visitors at each site, although the predatory ladybeetle Hippodamia convergens (Coccinellidae) and various Diptera (including species of Bombyliidae, Tachinidae and Syrphidae) were also common. Relatively few bees were collected: of the native species, most were members of the family Halictidae, while the few A. mellifera collected appeared to be mainly naïve (newly emerged) bees, with sparse pollen loads. The range of insect taxa collected differed at the two sites, and it seems likely that, in the U.S., the principal pollinators of jujube vary with location, with the differing pollination efficiencies of individual species being offset by the wide taxonomic range and high numbers of insects attracted to jujube flowers.