High Pollination Deficit and Strong Dependence on Honeybees in Pollination of Korla Fragrant Pear, Pyrus sinkiangensis

Abstract

Pollination deficits can compromise fruit yield and quality and have been reported in several fruit crops. It is unknown whether there is a pollination deficit in the production of Korla fragrant pear, Pyrus sinkiangensis, in China, and if so, whether this deficit can be mitigated by the use of managed honeybees (Apis mellifera). We assessed insect communities, flower visitation, pollination deficit and honeybee contribution to pear pollination in Korla fragrant pear orchards in Xinjiang, China. Insect communities were monitored using colored pan traps, and pollination deficit was assessed by comparing fruit set with open pollination to that with hand pollination in orchards without beehives from 2018 to 2021. The contribution of honeybees to pollination was assessed by comparing flower visitation, fruit set and fruit quality in pear orchards with and without beehives in 2020 and 2021. In orchards without beehives, wild bees (72%) were the dominant pollinator group in pan traps, followed by honeybees (15%), moths, hoverflies, butterflies and wasps (Vespidae). Fruit set in these orchards was much lower with open pollination (8 ± 2%) than with hand pollination (74 ± 4%). When comparing pollination in orchards with and without beehives in 2020 and 2021, we found that honeybees were responsible for most of the flower visits in orchards with (96%) and without beehives (66%). Wild bees were responsible for 1% and 6% of flower visits in orchards with and without beehives, respectively. Fruit set was significantly higher in orchards with beehives (38 ± 9%) than in orchards without beehives (12 ± 3%), while fruit set and sugar content were positively associated with pollinator visitation rate. The findings reveal a large pollination deficit in Korla fragrant pear orchards, and show that this deficit can be mitigated using managed honeybees.

Synthetic Nasonov gland pheromone enhances abundance and visitation of honeybee, Apis mellifera, in Korla fragrant pear, Pyrus sinkiangensis

“…NGP also resulted in higher honeybee abundance in mixed pear-apricot orchards. As insect pollination is a limiting factor in Korla fragrant pear (Li et al, 2022), these findings suggest that NGP has a potential to improve crop pollination by honeybees in this crop.…”

“…However, our results show that honeybee abundance in pan traps was strongly correlated with pear flower visitation rate, indicating that honeybee abundance in pan traps is a useful indicator for pear flower visitation. Furthermore, in a 2‐year study we showed that honeybee visitation rates were positively associated with initial fruit set and sugar content, but not fruit weight (Li et al, 2022). In addition, the effectiveness of NGP on fruit set and quality has also been reported in Guava and kiwifruit in India (Anita et al, 2012; Jailyang et al, 2022).…”

“…The increased visitation of honeybees to pear flowers could result in depletion of nectar in pear and/or increase the interference of different pollinator species (Weekers et al, 2022). However, even though wild pollinator species, such as wild bees, hoverflies and other flies, are common in pear orchards, their pear visitation rates are relatively low as compared to honeybees (Li et al, 2022). Based on this preliminary evaluation, the risks of using NGP in pear orchards are likely to be limited as compared to the risks of, for instance, the high agrochemical input in these orchards.…”

“…When NGP lures were applied to all trees in pear orchards this lead to a 2.2-fold higher honeybee abundance in pan traps compared to orchards without NGP lures, but only when there were beehives in the orchard. When no beehives were present in the orchards the honeybee abundance was low, and most likely constrained fruit set (Li et al, 2022). Obviously, if there are no or only few honeybees present in the orchard, the use of NGP will not be meaningful (Delaplane & Mayer, 2000).…”

“…Like most rosaceous plants, Korla fragrant pear is a self‐incompatible species that requires cross‐pollination by insects with a compatible cultivar to set fruit (De Franceschi et al, 2012). There is a large pollination deficit in Korla fragrant pear and this deficit can be mitigated by using beehives with managed honeybees, Apis mellifera (Li et al, 2022). While Korla fragrant pear is usually grown in monocultures, it is also grown in mixed pear‐apricot orchards.…”