Pests and predators on genetically altered cotton (Bt-cotton) and associated host plants in South Africa
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Date
2009-09-23
Authors
Bennett, Annette
Journal Title
Journal ISSN
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Publisher
University of the Free State
Abstract
The efficacy of the Bt-genes (the cry1Ac and cry2Ab2 genes) were evaluated for bollworms (i.e. the American or “African” bollworm, Helicoverpa armigera, the red bollworm Diparopsis castanea and the spiny bollworm species, Earias biplaga and E. insulana) on cotton under normal spraying conditions in different field trials in South Africa. Differences that were found in bollworm efficacy and yields are explained by comparison in various field trials. Bt-cottons (Genetically Modified Cotton) exhibiting either only bollworm resistance (NuOPAL), or cotton exhibiting both bollworm resistance and herbicide tolerance (NuOpal RR)-, or cotton exhibiting only herbicide tolerance
(DeltaOpal RR) were compared with non-Bt-cotton (DeltaOPAL). At the same time the effect of the Bt-gene on non-target organisms, such as secondary pests and predator numbers was monitored. Since most of the small-scale farmers in South Africa cultivate Bt-cotton and they are required to plant a refuge as part of a Resistance Management Programme, the abundance of alternative host plants for bollworms was evaluated in the largest small-scale production region, the Makhathini Flats (KwaZulu-Natal). Finally, the acceptance of Bt-technology amongst growers are discussed. This study was undertaken over a number of years and the repetition of a number of the trials at different localities has showed that Bt-technology has proved to be not only effective against the target pests, which are the african bollworms on cotton, but it is also beneficial to farmers in the form of a higher yield production and improved crop protection. The effect of the Bt-gene on non-target organisms is minimal if present and the Bt-gene has no detrimental effect on predator numbers, especially in the presence of an increase in insect host numbers, irrelative of the cotton type planted. The increase in predator numbers and secondary
pests is a result of the decrease in the number of bollworm sprays applied on Bt-cottons to control bollworm, as bollworms are effectively controlled by the Bt-gene. In some instances when additional sprays for secondary pests were applied, the benefit for the grower to plant Bt-cottons, is reflected in the higher yields and lower input costs as a result of the absence or fewer bollworm sprays. The host plant study showed that alternative host plant abundance in an area where cotton is cultivated, can provided evidence for a possible alternative refuge to conventional cotton. The fact that very little, of the cotton planted by South African farmers are conventional cotton (non-Bt-cotton) varieties, confirms the acceptance of Bt-technology amongst cotton growers, with full acceptance of the requirements of planting this cotton, while obtaining higher yields per surface area than in the case of non-Bt-cottons. The benefits of planting Bt-cotton that
have been illustrated in this study, clearly demonstrates the acceptance of Bt-cotton in South Africa, especially amongst, the commercial and the small-scale farmer, by enabling cotton growers to farm more cost-effectively.
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Keywords
Cotton -- Diseases and pests -- South Africa, Parasitic insects -- Host plants, Heliothis zea, Thesis (Ph.D. (Zoology and Entomology))--University of the Free State, 2007