81 Adv. Hort. Sci., 2009 23(2): 81-86 Received for publication 28 May 2008. Accepted for publication 28 November 2008. Distance from honeybee colonies and raceme order affect Prosopis juliflora (Sw.) DC. flower pollination and seed set S. Zaitoun*, A. Al-Majeed Al-Ghzawi**, N.H. Samarah* * Department of Plant Production and Protection, Faculty of Agricultural Technology, Al-Balqa’ Applied University, Al-Salt, Jordan. ** Department of Plant Production, Faculty of Agriculture, Jordan University of Science and Technology, P. O. Box 3030, Irbid, Jordan. Key words: colony distance, pollination, Prosopis juliflora, raceme. Abstract: An experiment was conducted in the Jordan Valley, Jordan to examine the effect of the order of flow- ering of racemes and the distance of bee hives from flowering trees on pod set, seed set, and pod characteristics of Prosopis juliflora. Flowers of Prosopis were subjected to three pollination treatments: i) open pollination; ii) open pollination plus removal of first raceme; and iii) supplementary pollination plus removal of first raceme. Trees were selected at three distances from the bee hives (0, 2, and 4 km). Number of pods per node for open pol- lination treatment tended to decrease with the decrease in raceme order on the flowering node. Removal of raceme improved pod set in the consequent ordering raceme as compared with open pollination treatment. The pollination treatment x distance interaction was significant for pod number and weight. Supplementary pollina- tion plus removal gave higher pod number per node than other pollination treatments. The role of honeybees in Prosopis flower pollination is restricted to the nearest trees; trees should not be more than 2 km from the bee hives to improve pod set and seed yield. 1. Introduction A major problem that limits livestock production in Jordan and other arid regions around the world is the high cost of animal feed. This is mainly due to an acute shortage of fresh water, limiting the utilization of arable land for the production of food for human and animal consumption. There are some readily available livestock feeds for natural-range grazing and browsing land as well as agricultural by-products such as pods of carob (Ceratonia siliqua) (El-Shatnawi and Ereifj, 2001), husks from olive mills (Olea europaea) (Al Jas- sim et al., 1997) and Prosopis pods (Abdullah and Abdelhafez, 2004). In the last two decades, mesquite trees, Prosopis juliflora, have been planted abundantly in semiarid regions of Jordan, including the Jordan Val- ley. Prosopis trees are grown for landscaping under irrigation; mostly when used as windbreaks they grow and produce an inconsistent pod yield in Jordan and other countries (Solbrig and Cantino, 1975; Oliveira and Pires, 1990; Pasieczink et al., 2001; Abdullah and Abdelhafez, 2004). The flowering period which extends from early Sep- tember to late January in Wadi Araba may not be suit- able for pollination of flowering plants that require insect pollinators because most wild bees are in estiva- tions. As mesquite trees grow in a healthy state with a canopy reaching 5 m high, low pod yield and seasonal pod yield variation may be due to pollination problems. Flower pollination is mainly affected by different factors such as insufficient pollen receipt (Lee, 1988; Berry and Calvo, 1991; Brunet and Charlesworth, 1995), competition among ovaries of the same inflo- rescence for a limited source of nutrients (Bawa and Webb, 1984; Guitián, 1994; Medrano et al., 2000), and differences in the positions within the inflorescence (Lee, 1988; Berry and Calvo, 1991; Diggle, 1995), for which the fruit set of late-opening flowers is not affect- ed by the removal of early-opening flowers or the pre- vention of their fruiting (Sutherland, 1987; Berry and Calvo, 1991). Prosopis juliflora is a self-incompatible plant that requires cross-pollination for seed set (Pasieczink et al., 2001). Under Jordanian conditions, Prosopis blooms in late summer and winter. Honey bees (Apis mellifera L.) act as primary pollinators for Prosopis juliflora (Sw.) DC., since wild bees seldom pollinate its