Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Insect pollination contributes in various degrees toward the production of a variety of
agricultural crops that ensure diversity and nutritional value in the human diet. Although
managed honeybees (Apis mellifera L.) are still the most economically valuable pollinators of
monoculture crops cultivated globally, wild pollinator communities can contribute
substantially toward crop pollination through pollination ecosystem services sourced from
neighbouring natural habitats. Pollination ecosystem services are thus valuable and can
motivate for the protection of natural ecosystems hosting diverse insect pollinator
communities. F1 onion hybrid seed production is entirely dependent on high insect pollinator
activity to ensure cross pollination, seed set and profitable seed yields. Data was collected on
18 onion hybrid seed crops grown in the semi‐arid Klein Karoo and southern Karoo regions of
the Western Cape, South Africa. These two main production regions are located within the
Succulent Karoo biome, recognized as a global biodiversity hotspot of especially high plant
diversity. It is also habitat to the indigenous Cape honeybee (Apis mellifera capensis Esch.).
Sites selected varied in the percentages of available natural habitat and managed honeybee
hives stocking density. Diverse anthophile assemblages were sampled with pan traps within
all the onion fields, regardless of the percentage of available natural habitat near the crop.
Crop management practices significantly affected the diversity of anthophile species caught
within onion fields, although less than 20% of this diversity was observed actually visiting
onion flowers. The honeybee (managed and wild) was by far the most important pollinator
because of its high visitation frequency and regular substantial onion pollen loads carried on
their bodies. Honeybee visitation significantly increased onion hybrid seed yield, while
anthophile diversity and non‐Apis visitation had no effect on seed yield. Neither managed
hive density, nor percentage natural habitat were important in determining honeybee
visitation or seed yield. Total annual rainfall was the only significant factor determining
honeybee visitation. Secondary factors caused by rainfall variability, such as wild flower
abundance or soil moisture, may have significantly affected honeybee visitation. In addition,
the positive correlation between honeybee visitation and the diversity of hand‐sampled
insects from onion flowers; indicate that either or both onion varietal attractiveness and/or
pollinator population size may have had significant effects on overall insect visitation.
Honeybees showed marked discrimination between hybrid onion parental lines and preferred
to forage on one or the other during single foraging trips. Hybrid onion parents differed
significantly in nectar characteristics and onion flower scent which would encourage selective
foraging through floral constancy. Interspecies interactions were insignificant in causing increased honeybee pollination because of the scarcity of non‐Apis visitors. Most farming
practices are subjected to favourable environmental conditions for successful production.
However, and especially in the South African context, the dependence of onion hybrid seed
crops on insect pollination for successful yields, increase its reliance on natural ecosystem
dynamics that may deliver abundant wild honeybee pollinators, or attract them away from
the crops. Nevertheless, this dependence can be mitigated effectively by the use of managed
honeybee colonies to supplement wild honeybee workers on the flowers. / AFRIKAANSE OPSOMMING: Insek bestuiwing dra in verskillende grade by tot die produksie van landbou gewasse wat
variteit en voedingswaarde in die mens se dieet verseker. Al is die heuningby (Apis mellifera
L.) steeds die waardevolste ekonomiese bestuiwer van verboude enkelgewasse, kan wilde
bestuiwers wesenlik bydra tot gewasbestuiwing deur middel van ekosisteem dienste
afkomstig van natuurlike habitatte. Bestuiwing ekosisteem dienste is daarom waardevol en
kan dus die bewaring van natuurlike ekosisteme, wat diverse gemeenskappe huisves,
regverdig. F1 basterui saadproduksie is totaal afhanklik van hoë insek‐bestuiwer aktiwiteit
om kruisbestuiwing, saadvorming en winsgewende saadopbrengste te verseker. Data is
ingesamel op 18 basterui saad aanplantings in die half‐droë Klein Karoo en suid‐Karoo streke
van die Weskaap, Suid‐Afrika. Hierdie twee hoof produksie streke is geleë binne die
Sukkulente Karoo bioom wat erken word as ʼn globale biodiversiteits “hotspot” met hoë plant
diversiteit. Dit is ook die habitat van die inheemse Kaapse heuningby (Apis mellifera capensis
Esch.). Aanplantings is gekies om verskillende grade van beskikbare natuurlike habitat en
bestuurde heuningby korf digthede te verteenwoordig. Diverse versamelings blom‐besoekers
is versamel met water‐wippe in al die aanplantings, ongeag die persentasie natuurlike habitat
beskikbaar by elke aanplanting. Gewas bestuurspraktyke het die diversiteit van blombesoekers
betekenisvol beïnvloed. Tog is minder as 20% van hierdie diversiteit as aktiewe
besoekers op die uiekoppe waargeneem. Heuningbye (bestuur of wild) was oorwegend die
belangrikste bestuiwers as gevolg van hoë besoek frekwensies en wesenlike ladings
uiestuifmeel op hulle liggame. Heuningby besoeke het saadopbrengs betekenisvol verhoog,
maar blom‐besoeker diversiteit en nie‐Apis besoeke het geen effek op saadopbrengs gehad
nie. Bestuurde korf digtheid en persentasie natuurlike habitat was nie belangrik in die
bepaling van heuningby besoeke of basterui saadopbrengste nie. Totale jaarlikse reënval was
die enigste betekenisvolle faktor wat heuningby besoeke bepaal het. Sekondêre faktore wat
versoorsaak word deur reënval veranderlikheid, soos veldblom volopheid of grondvog, kon
betekenisvolle effekte op die aantal heuningby besoeke gehad het. Bykomend, dui die
positiewe korrelasie tussen heuningby besoeke en die diversiteit van hand‐versamelde
insekte vanaf die uiekoppe op die moontlike betekenisvolle effek van elk of beide basterui
variteit aantreklikheid en/of bestuiwer populasie grote op algehele insek besoeke.
Heuningbye het noemenswaardige diskriminasie getoon tussen die basterui ouerlyne en het
verkies om op een of die ander te wei tydens enkele weidingstogte. Basterui ouerlyne het
betekenisvol verskil in nektar eienskappe en blomgeur wat die selektiewe weiding van
heuningbye, toegepas deur blomkonstantheid, sal aanmoedig. Tussen‐spesie interaksies was onbetekenisvol in die verhoging van heuningby bestuiwing omdat nie‐Apis besoekers baie
skaars was. Meeste boerdery praktyke is onderhewig aan gunstige omgewings toestande vir
suksesvolle produksie. Maar, en veral in die Suid‐Afrikaanse konteks, omdat basterui saad
aanplantings afhanklik is van insek bestuiwing vir suksesvolle opbrengste, word daar meer
staat gemaak op natuurlike ekosisteem dinamika wat volop wilde heuningby bestuiwers kan
voorsien, of selfs bestuiwers van die aanplanting kan weg lok. Nietemin, hierdie afhanklikheid
kan effektief verlaag word deur die gebruik van bestuurde heuningby kolonies om die aantal
wilde heuningby werkers op die blomme aan te vul.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86238 |
| Date | 04 1900 |
| Creators | Brand, Mariette Rieks |
| Contributors | Samways, Michael J., Veldtman, Ruan, Colville, Jonathan F., Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xviii, 168 p. : ill. |
| Rights | Stellenbosch University |
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