Buzz-Pollinated Crops: A Global Review and Meta-analysis of the Effects of Supplemental Bee Pollination in Tomato

Buzz-pollinated plants require visitation from vibration producing bee species to elicit full pollen release. Several important food crops are buzz-pollinated including tomato, eggplant, kiwi, and blueberry. Although more than half of all bee species can buzz pollinate, the most commonly deployed supplemental pollinator, Apis mellifera L. (Hymenoptera: Apidae; honey bees), cannot produce vibrations to remove pollen. Here, we provide a list of buzz-pollinated food crops and discuss the extent to which they rely on pollination by vibration-producing bees. We then use the most commonly cultivated of these crops, the tomato, Solanum lycopersicum L. (Solanales: Solanaceae), as a case study to investigate the effect of different pollination treatments on aspects of fruit quality. Following a systematic review of the literature, we statistically analyzed 71 experiments from 24 studies across different geopolitical regions and conducted a meta-analysis on a subset of 21 of these experiments. Our results show that both supplemental pollination by buzz-pollinating bees and open pollination by assemblages of bees, which include buzz pollinators, significantly increase tomato fruit weight compared to a no-pollination control. In contrast, auxin treatment, artificial mechanical vibrations, or supplemental pollination by non-buzz-pollinating bees (including Apis spp.), do not significantly increase fruit weight. Finally, we compare strategies for providing bee pollination in tomato cultivation around the globe and highlight how using buzz-pollinating bees might improve tomato yield, particularly in some geographic regions. We conclude that employing native, wild buzz pollinators can deliver important economic benefits with reduced environmental risks and increased advantages for both developed and emerging economies.

Pollen limitation and reproduction varies with population size in experimental populations of Sabatia angularis (Gentianaceae)

Individuals in large plant populations are expected to benefit from increased reproductive success relative to those in small populations because of the facilitative effects of large aggregations on pollination. As populations become small, the inability to attract sufficient numbers of pollinators can reduce reproduction via pollen limitation. This study experimentally tested whether such trends occur for the herbaceous biennial Sabatia angularis (L.) Pursh (Gentianaceae). We created artificial populations of varying size consisting of potted S. angularis plants in two field sites to determine whether population size affected mean fruit and seed set. We also examined whether population size affected the degree of pollen limitation using a supplemental pollination design in one of the sites. Our results showed that, on average, seed set was lower in large populations, not small populations, of S. angularis and that this result may be due to increased pollen limitation in large populations. We suggest that in certain contexts, small populations may enjoy reproductive advantages over large populations by escaping intraspecific competition for pollinators.

SUPPLEMENTAL POLLINATION – INCREASING OLIVE (OLEA EUROPAEA) YIELDS IN HOT, ARID ENVIRONMENTS

In general, olive trees are self-compatible, but under some climatic conditions a number of cultivars have demonstrated problems with pollination and fruit set. The Manzanillo cultivar is usually self-pollinating, but under hot conditions its pollen develops slowly, resulting in little or no fertilization. Trials were carried out in two hot, arid ecosystems (Arid Chaco in La Rioja, Argentina and Sonoran Desert in Arizona, USA) to determine if supplemental pollination of a Manzanillo cultivar has the potential to increase yields, and to assess the effectiveness of three different cultivars as sources of pollen. Branches that received supplemental pollination produced 21% more total olives than the control. In Arizona, total olive and shotberry (unpollinated olive) production were significantly different between treatments. Branches that received supplemental pollination produced 98% more olives, and had 58% fewer shotberries than did branches in the control rows. Significantly more olives were produced on branches pollinated with Sevillano and Arbequina pollen, compared with those pollinated with Ascolano pollen and with the control.

Timing, magnitude and causes of flower and immature fruit loss in pin cherry and choke cherry

Pin cherry (Prunus pensylvanica L.) and choke cherry (Prunus virginiana L.) are two wild fruit species with potential for commercial production, but information about fruit production is limited. The objectives of this study were to determine, for both species, the timing and magnitude of flower and immature fruit loss, and to determine the primary causes of this loss, including the effects of pollen source and supplemental pollination. Sequential sampling of both pin cherry and choke cherry indicated that the primary period of abscission occurred during the first 3 wk following full bloom. Final fruit set ranged from 32.6 to 44.7% of flower number for pin cherry, and from 3.7 to 20.1% for choke cherry. Insect damage accounted for only 14% of the total observed flower and fruit abscissions in pin cherry and 7% in choke cherry. The major insect pest causing this loss in pin cherry was a sawfly (Hoplocampasp., Tenthredinidae) and in choke cherry, a leaf-roller (Archips argyrospila, Tortricidae). A controlled pollination experiment was used to determine the effects of pollen source and supplemental pollination on pin cherry and choke cherry. Final fruit set for flowers that were cross-pollinated by hand in both pin cherry (mean of 51.3%) and choke cherry (mean of 56.9%) in most cases was significantly greater than flowers that were open-pollinated, self-pollinated, or not pollinated. These data suggested that the majority of flower and immature fruit loss in both pin cherry and choke cherry resulted from a lack of pollination and/or fertilization. Key words: Choke cherry, pin cherry, flower loss, immature fruit loss, pollination, insect damage

Use Yield Ratios to Evaluate Effects of Supplemental Pollination on Crop Production

The environment caused large fluctuations in almond yields from year-to-year, which confounded analysis of pollination treatments performed in the field. Following the practice of supplemental pollination, there was insufficient improvement in yield to indicate that extra pollen applied to honey bees affected nut production. However, when yield for a cultivar exposed to extra pollen was compared to an untreated, reference cultivar grown in the same field, a statistically significant increase in yield was detected. Coefficients of variation for yield ratios averaged 54% lower than for yields alone in each of eight orchards examined. Converting annual yields to yield ratios mitigated the effects of the environment on analysis of production data.

Testing a Power Duster for Pollination of `McIntosh' Apples

This study was undertaken to test the efficacy of a power duster for supplemental pollination of `McIntosh' apple trees, where lack of nearby pollinizing cultivars was thought to be a limiting factor to productivity. The pollen duster was ineffective in increasing fruit set, fruit size, or seed number in fruits on limbs that were covered with spun-bonded rowcover material prior to bloom. Applying supplemental pollen to open-pollinated `McIntosh' trees had no effect on fruit set, yield, fruit size, or seed number, regardless of pollen dose, timing, or number of applications. Dispersal of supplemental pollen with a power duster appears to be an inefficient method of pollinating apple trees.