CHEMICAL COMPOSITION OF ATTRACTIVE BLENDS IN SELECTED OCIMUM SPECIES TRADITIONALLY USED TO LURE HONEY BEES

Abstract

The success of sustainable beekeeping depends on possibility of establishing a bee colony. Low hive occupation rate has been identified as one of the prominent challenges facing beekeeping sector in addition to pest attacks, inadequate skills in hive management and poor apiary conditions. To initiate prompt hive colonization, some beekeepers traditionally use aromatic herbs and shrubs to smoke interior parts of a new hive. However, there is limited scientific evidence supporting the traditional use of aromatic plants as honey bee swarm lures. The aim of this study was to establish the chemical basis of the use of indigenous plants as honey bee lures. Essential oils, fresh and smoldered volatiles of three Ocimum species namely; O. kilimandscharicum, O. kenyense and O. lamiifolium were investigated for their chemical compositions and potential to lure bees. Gas Chromatography-Mass Spectrometry (GC-MS) analysis was used to determine chemical composition of volatiles of the Ocimum species. Dual choice Y-tube olfactometer experiments were used to determine the attraction of honey bees (Apis mellifera scutellata) to choices of essential oil, fresh and smoldered volatiles against negative and positive controls. Swarm luring activity of most attractive Ocimum species’ volatiles was tested in the field in an 8 by 8 randomized Latin square block experiment. There were notable variations in chemical constituents of the studied Ocimum species based on species, agro ecological zone and mode of extraction. Monoterpenoids (49.1-75.1%), benzenoids (28.9-43.9%) and sesquiterpenoids (2.13-37.7%) were the major classes of natural products characterizing respective volatiles of O. kilimandscharicum, O. kenyense and O. lamiifolium species. (Eucalyptol, estragole and β-pinene), (camphor, linalool and eucalyptol) and (α-phellandrene and β-sabinene) were identified as major chemical constituents of essential oil, fresh and smoldered volatiles of O. kenyense, O. kilimandscharicum and O. lamiifolium species, respectively. This study reports α-phellandrene chemotype of O. lamiifolium species’ essential oil for the first time. In olfactometric tests, attraction of honey bees to smoldered, fresh and essential oil volatiles varied significantly (p<0.05) with mean values of attracted bees of 7.16 ± 0.22, 6.81 ± 0.28 and 4.56 ± 0.40, respectively. Smoldered volatiles of O. kilimandscharicum-Kirinyaga (OKI-KRN), O. kenyense-Nyeri (OKE-NYR) and O. kilimandscharicum-Nyeri (OKI-NYR) were more attractive as compared to other investigated volatiles, with respective mean values of attracted bees of 8.17 ± 0.17, 7.67 ± 0.21 and 7.17 ± 0.17. In field bioassay, smoldered volatiles of OKI-NYR and OKI-KRN were the most effective honey bee luring treatments with mean hive occupation times of 29 and 30 days, respectively. Synthetic blends of fresh and smoldered volatiles of OKI-NYR, OKE-NYR and OKI-KRN were prepared using major constituents identified in GC-MS analysis and. Subtraction bioassays of synthetic blends of smoldered volatiles of OKI-NYR, OKE-NYR and OKI-KRN were conducted to determine the specific chemical constituents that contributed to their respective bee attractant activity. A blend comprising of geraniol, nerol, neryl acetate, eucalyptol, estragole, (E)-β-ocimene, (E)-β-caryophyllene, (E)-β-farnesene and α-humulene (SBAC1) was identified as a promising lead towards formulation of a potent bee lure with MEC50 and MEC75 values of 6.9 and 15.4 μg/μl, respectively. Findings of this study have demonstrated that chemo-ecological interactions of honey bees and aromatic plants are very crucial in prompting bee hive colonization, which in turn has the potential to contribute towards food security, manufacturing and poverty reduction thus addressing some aspects of Kenya government’s big four agenda.