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dc.contributor.advisorDu Plessis, M.J.
dc.contributor.advisorVan den Berg, J.
dc.contributor.authorFourie, Desireé
dc.date.accessioned2016-07-25T07:34:57Z
dc.date.available2016-07-25T07:34:57Z
dc.date.issued2016
dc.identifier.urihttp://hdl.handle.net/10394/18030
dc.descriptionMSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2016en_US
dc.description.abstractGenetically modified cotton expressing Bacillus thuringiensis (Bt) proteins has been cultivated in South Africa since 1998 for control of the bollworm complex. Spiny bollworms, Earias biplaga (Walker) (Lepidoptera: Noctuidae) and Earias insulana (Boisduval) (Lepidoptera: Noctuidae) belong to this complex. Exposure to Bt crops could contribute to resistance development to the insecticidal proteins expressed in these crops. The aim of this study was to determine the efficacy of Bt proteins for control of and the effect of temperature on development of E. biplaga in South Africa. There is currently no resistance of E. biplaga to Bollgard® and Bollgard II® cotton in South Africa. The use of Bt spray applications for control of E. biplaga on cotton was also evaluated, although it is currently not registered for control of this pest on cotton in South Africa. Half the dosage rate registered for bollworm control on cotton, was too low for effective control. The recommended dosage rate controlled the larvae as effective as Bollgard® and Bollgard II®, but 100% mortality was not achieved. Environmental factors such as UV light and rain may reduce the efficacy of Bt sprays. The final instar larvae might not be controlled by Bt sprays. Effective coverage with the spray application is essential for successful control. The effect of temperature on the development of E. biplaga was studied at four different temperature regimes, namely 18, 20, 25 and 30 ± 1°C. Development time for all life stages was inversely related to temperatures from 18 to 30 °C. The relationship between temperature and developmental rate of E. biplaga was linear between 18 and 30 °C and more rapid development was observed with increasing temperatures. The total development period was 68.9 to 22.5 days at 18 and 30 days, respectively. The thermal thresholds for E. biplaga were 15.2, 11.3, 12.8 and 12.2°C and the thermal constants were 34.3, 195.1, 156.45 and 369.6 °D, for the completion of the egg, larval, pupal and egg-to-adult stages, respectively.en_US
dc.language.isoenen_US
dc.publisherNorth-West University (South Africa) , Potchefstroom Campusen_US
dc.subjectBacillus thuringiensisen_US
dc.subjectBt sprayen_US
dc.subjectEarias biplagaen_US
dc.subjectDegree-daysen_US
dc.subjectDevelopmenten_US
dc.subjectResistanceen_US
dc.subjectTemperatureen_US
dc.titleEfficacy of Bt proteins and the effect of temperature on the development of spiny bollworm in South Africaen_US
dc.typeThesisen_US
dc.description.thesistypeMastersen_US


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