Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti Supplementing bumblebees to ‘Mauritius’ lychee improves yield G. Sapir a , M. Goldway a,b , R.A. Stern a,b, ⁎ a MIGAL – Galilee Research Institute, P.O. Box 831, Kiryat Shemona 11016, Israel b Department of Biotechnology, Faculty of Life Sciences, Tel-Hai College, Upper Galilee 12210, Israel ARTICLEINFO Keywords: Litchi chinensis Pollination Honeybee Bumblebee Fruit set Yield ABSTRACT Honeybees (HB) are strongly attracted to lychee flowers and serve as the main pollen vector in most lychee orchards throughout the world. Despite precise protocols for managing HB in Israeli lychee orchards, we sus- pected that the full pollination potential of the orchards was not being achieved and that yields could be in- creased. Since bumblebees (BB) forage in harsh weather and at lower temperatures than HB, in previous studies we questioned if adding BB to HB in apple and pear orchards would increase fruit set and yield. Encouraged by the important results, we examined this approach in lychee in the present work. The experiments were con- ducted for three years, resulting in a significant increase in lychee fruit set and yield. Our observations revealed that BB contribute to lychee pollination not only because they are active in conditions that HB are not, but also because HB collect mainly nectar from the lychee flowers and barely contact the reproductive organs, while BB collectmainlypollenandhencepollinationincreases.Asaresultofthiswork,since201810BBhivesperhectare have been introduced into many lychee orchards in Israel in addition to the standard 2.5 HB hives per hectare. 1. Introduction Low fertility of many fruit trees can arise due to various reasons, such as low flowering intensity, abnormal development of male and/or female reproductive organs, inadequate pollination, failure during the double fertilization in the ovule and finally pre-harvest fruit drop (Monselise, 1986; Westwood, 1993; Janick and Paull, 2003; Tromp et al., 2005). In lychee there are three types of flowers which bloom sequentially on the same inflorescence; male 1 (M1) flower first then the female (F) flower and finally male 2 (M2) flower (Fig. 1). The pollen grains of M2 flowers are more viable than M1 flowers (Stern and Gazit, 1998).Ina single inflorescence, the bloom of each type does not overlap with the others, thus self pollen transfer among flowers of the same panicle does not occur. However, the bloom of different inflorescences on a tree is not synchronized. Hence pollination can accrue between flowers of different inflorescences on the same tree (Joubert, 1986). Honeybees (HB) are strongly attracted to lychee flowers, especially to its nectar (Stern and Gazit, 1996), and serve as the lychee’s main pollinator in most orchards throughout the world. Therefore, lack of pollination was not considered a limiting factor for lychee yield (McGregor, 1976; Menzel, 1984; Joubert, 1986; DeGrandi-Hoffman, 1987; King et al., 1989; Free, 1993; Stern et al., 1993; Stern and Gazit, 1996, 2003). Still, Chen (1993) proposed that since the origin of lychee is in southern China (Huang et al., 2005), its native pollinator was probablytheendemicChineseHB(A.ceranacerana),andpollinationby the European HB might be insufficient (Stern and Gazit, 2003). In re- cent experiments conducted in Israel in pear and apple orchards, it was shown that introducing bumblebees (BB: Bombus terrestris L.) together withHBenhancedpollination,resultinginasignificantimprovementin fertility (Zisovich et al., 2012; Sapir et al., 2017). In addition, Zhang etal.(2015),whohadstudiedpeachpollinationinagreenhouse,found thattheadditionofBBtoHBimprovedfruitsetandfruitsizecompared to pollination only with HB. They suggested that this was due to an increase in pollen grains that had reached the stigma that led to faster germination and completion of the fertilization process. Similar results werefoundinAsianpear (Pyruspyrifolia) pollinated abundantly (Zhang et al., 2010). BB have several attributes that are beneficial for pollination. Like HB, BB collect nectar and pollen from numerous sources (Heinrich, 2004), however the BB’s capacity to carry nectar and pollen is greater) Free and Williams, 1972) as their body is about twice as large (Heinrich, 2004). In addition, in each foraging trip, BB generally visit many more flowers than HB (Goodell and Thomson, 1997; Zisovich et al., 2012; Sapir et al., 2017). Moreover, BB forage at temperatures below 14°C, the limiting temperature for HB activity (Vicens and Bosch, 2000; Sapir et al., 2017), and in harsh conditions (Goulson, 2010). Hence, BB pollination can commence earlier in the day and is https://doi.org/10.1016/j.scienta.2019.03.015 Received 13 January 2019; Received in revised form 6 March 2019; Accepted 8 March 2019 ⁎ Corresponding author at: MIGAL – Galilee Research Institute, P.O. Box 831, Kiryat Shemona 11016, Israel. E-mail address: raffi@migal.org.il (R.A. Stern). Scientia Horticulturae 251 (2019) 162–166 0304-4238/ © 2019 Elsevier B.V. All rights reserved. T