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Formulation and optimisation of entomopathogenic nematodes for long-term storage and application against key insect pests
Thesis (MScConsEcol)--Stellenbosch University, 2021.
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2021
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| _version_ | 1867613931196907520 |
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| access_status_str | Open Access |
| author | Nxitywa, Abongile |
| author2 | Malan, Antoinette P. |
| author_browse | Malan, Antoinette P. Nxitywa, Abongile |
| author_facet | Malan, Antoinette P. Nxitywa, Abongile |
| author_sort | Nxitywa, Abongile |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MScConsEcol)--Stellenbosch University, 2021. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/109842 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:43:58.501Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/109842 Formulation and optimisation of entomopathogenic nematodes for long-term storage and application against key insect pests Nxitywa, Abongile Malan, Antoinette P. Cloete, Mia Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology. Agricultural industries -- South Africa Insect nematodes -- Effect of temperature on Entomopathogenic nematodes Nematodes as biological pest control agents -- South Africa UCTD Thesis (MScConsEcol)--Stellenbosch University, 2021. ENGLISH ABSTRACT: Pest insect infestation is a key challenge to crop production in the agricultural industry. To reduce crop losses, farmers use chemical pesticides. The continuous use of pesticides lead to the development of insecticide resistance. Entomopathogenic nematodes (EPNs) have been found to be effective against key insect pests. However, their commercialisation as biological control agents is impaired by their short shelf life. Therefore, there is a dire need to develop a preservation method that can improve their storage, without negatively affecting their infectivity against the target pest insects. In this study, two in vitro-cultured South African isolates of EPNs, Steinernema jeffreyense and S. yirgalemense, were investigated for their storage stability in different formulations, stored at different temperatures. The formulation techniques included the use of diatomaceous earth (DE), alginate beads and gels. Pathogenicity tests for all the formulations were done using Tenebrio molitor (mealworms). Nipagin and Procydin were added to DE formulations as antimicrobial agents. For the DE formulation, both the species were investigated and stored at room temperature (RT), at 14 ℃ and 25 ℃, and monitored weekly, for a period of 8 weeks. For both species, the survival and pathogenicity of the formulated IJs stored at 14 ℃ were higher compared to those stored at 25 ℃, and at RT. The addition of antimicrobial agents prevented contamination, compared to the controls. To improve storage stability and to reduce the amount of IJs escaping from the beads, S. yirgalemense was encapsulated in alginate beads and the impact of three factors were investigated; sodium alginate (2% and 4%), calcium chloride (0.5% and 2%) and the different bead-hardening times (20 min and 60 min). The beads were stored at a constant 25 ℃ and monitored weekly for 6 weeks. This study found that the alginate percentage was the most important factor in preventing the infective juveniles (IJs) from escaping from the beads. All tested factors had no influence on the pathogenicity of the IJs, considering that the mortality of T. molitor remained above 70%. Lastly, the storage stability of S. yirgalemense was investigated through the use of two different types of agar, that is, STOCKOSORB® 660 and a novel developed cellulose nanofiber gel. The formulations were stored at a constant 25 ℃ and monitored weekly for a period of 6 weeks. These results revealed that the novel nanofiber gels are not suitable for the storage of S. yirgalemense IJs. The soft agar gels (1% and 1.5%) were found to have a mean percentage ranging from 77 - 82% after 6 weeks in comparison to IJs that were formulated in 1 g of STOCKOSORB® 660 in 50 ml water which had a 80% mean survival rate. The STOCKOSORB® 660-stored IJs were more pathogenic against mealworms than IJs in agar. The current study proved that South African EPN species have the ability to maintain a shelf life of up to 8 weeks, indicating that there is a high potential for their commercialisation. However, more research in large-scale field trials for effectivivity testsing and field persistence is still required. AFRIKAANSE OPSOMMING: Besmetting deur pesinsekte is ʼn belangrike uitdaging vir gewasproduksie in die landboubedryf. Om oesverliese te verminder, gebruik boere meestal chemiese plaagdoders. Die deurlopende gebruik van plaagdoders kan lei tot die ontwikkeling van weerstand teen die produkte. Daar is gevind dat entomopatogenies nematodes (EPNs) effektief is teen die belangrike pesinsekte. Die kommersialisering daarvan as biologiese beheermiddel word egter benadeel deur die kort rakleeftyd. Daar is dus ʼn dringende behoefte om ʼn formulerings metode te ontwikkel wat die stoor van nematodes kan verbeter, sonder dat infeksie teen die teikenplaaginsekte negatief beïnvloed word. In hierdie studie is twee in vitro gekweekte Suid-Afrikaanse EPN isolate, Steinernema jeffreyense en S. yirgalemense, ondersoek vir hul storingstabiliteit in verskillende formulasies by verskillende temperature. Die formuleringstegnieke het die gebruik van diatoomaarde (DE), alginaat korrels en gels ingesluit. Patogenisiteittoetse vir al die formulasies is met behulp van Tenebrio molitor (meelwurm) larwes gedoen. Nipagin en Procydin is as antimikrobiese-middels by die DE- formulerings gevoeg. Vir die DE-formulering is beide die spesies ondersoek en gestoor by kamertemperatuur (RT), by 14 °C sowel as by ʼn konstante 25 °C en weekliks gemonitor vir ʼn periode van 8 weke. Vir beide spesies was die oorlewing en patogeniteit van die geformuleerde infektiewe onvolwasse nematodes (IJs) wat by 14 °C gestoor is, hoër as in 25 °C en by RT. Die toevoeging van antimikrobiese middels het kontaminasie verhoed in vergelyking met die kontroles. Om die stabiliteit van die opberging te verbeter en die hoeveelheid IJs wat uit die alginaat korrels ontsnap te verminder, is S. yirgalemense, in die alginaat korrels geënkapsuleer en die effek van drie faktore is ondersoek: natriumalginaat (2% en 4%), kalsiumchloried (0,5% en 2%) en die verskillende korrel verhardingstye (20 min en 60 min). Die korrels is op ʼn konstante 25 °C gestoor en weekliks gemonitor vir 6 weke. Hierdie studie het bevind dat die presentasie alginaat die belangrikste faktor is om te verhoed dat die IJs uit die krale ontsnap. Alle getoetsde faktore het nie die patogeniteit van die IJs beïnvloed nie, aangesien die mortaliteit van T. molitor bo 70% gebly het. Laastens is die storingstabiliteit van S. yirgalemense ondersoek deur die gebruik van twee soorte agar, naamlik STOCKOSORB® 660 en ʼn nuut ontwikkelde sellulose nanovesel gel. Die formulasies is by ʼn konstante 25 °C gestoor en weekliks gemonitor oor ʼn 6 weke tydperk. Hierdie resultate het getoon dat die nuwe nanovesel gels nie geskik is vir die opberging van S. yirgalemense IJs nie. Daar is gevind dat sagte agar-gels (1% en 1.5%) na 6 weke ʼn gemiddelde oorlewingspersentasie van 77-82% toon, in vergelyking met IJs wat in 1 g STOCKOSORB® 660 in 50 ml water geformuleer is en ʼn gemiddelde oorlewing van 80% gehad het. Die STOCKOSORB® 660-gestoorde IJs was meer patogenies teen meelwurms as die IJs wat in agar formuleer is. Die huidige studie het bewys dat Suid-Afrikaans geïsoleerde EPN-spesies die vermoë besit om ʼn rakleeftyd van tot 8 weke te handhaaf, wat dui op ʼn groot kommersialiseringspotensiaal. Meer navorsing met grootskaalse veldproewe vir effektiwiteitstoetsing en nawerking in die veld is egter steeds nodig. Masters 2021-02-18T09:36:00Z 2021-04-21T14:28:34Z 2021-02-18T09:36:00Z 2021-04-21T14:28:34Z 2021-03 Thesis http://hdl.handle.net/10019.1/109842 en_ZA Stellenbosch University xvii, 100 pages : illustrations application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Agricultural industries -- South Africa Insect nematodes -- Effect of temperature on Entomopathogenic nematodes Nematodes as biological pest control agents -- South Africa UCTD Nxitywa, Abongile Formulation and optimisation of entomopathogenic nematodes for long-term storage and application against key insect pests |
| title | Formulation and optimisation of entomopathogenic nematodes for long-term storage and application against key insect pests |
| title_full | Formulation and optimisation of entomopathogenic nematodes for long-term storage and application against key insect pests |
| title_fullStr | Formulation and optimisation of entomopathogenic nematodes for long-term storage and application against key insect pests |
| title_full_unstemmed | Formulation and optimisation of entomopathogenic nematodes for long-term storage and application against key insect pests |
| title_short | Formulation and optimisation of entomopathogenic nematodes for long-term storage and application against key insect pests |
| title_sort | formulation and optimisation of entomopathogenic nematodes for long term storage and application against key insect pests |
| topic | Agricultural industries -- South Africa Insect nematodes -- Effect of temperature on Entomopathogenic nematodes Nematodes as biological pest control agents -- South Africa UCTD |
| url | http://hdl.handle.net/10019.1/109842 |
| work_keys_str_mv | AT nxitywaabongile formulationandoptimisationofentomopathogenicnematodesforlongtermstorageandapplicationagainstkeyinsectpests |