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Constraints on Neltumius arizonensis (Coleoptera: Bruchidae) as a biocontrol agent of prosopis in South Africa : the role of parasitoids
1. Two species of seed feeding bruchid, Algarobius prosopis and A. bottimeri, were introduced to South Africa in 1987 and 1990 respectively, to curb the spread of the invasive weed Prosopis. Failure of A. bottimeri to establish and reduced effectiveness of A. prosopis due to interference by livestoc...
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| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2017
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| Summary: | 1. Two species of seed feeding bruchid, Algarobius prosopis and A. bottimeri, were introduced to South Africa in 1987 and 1990 respectively, to curb the spread of the invasive weed Prosopis. Failure of A. bottimeri to establish and reduced effectiveness of A. prosopis due to interference by livestock resulted in the release of a third species, Neltumius arizonensis in 1992. 2. Algarobius prosopis populations have remained high but N. arizonensis has not been as successful. 3. Populations ofboth bruchids showed similar emergence patterns through the sampling period hence there is no temporal partitioning of resources. 4. Percentage emergence of N. arizonensis was low at the start of the season but increased as the season progressed with higher proportions of N. arizonensis emerging from 'tree' pods than 'ground' pods. Regardless of the spatial partitioning of resources by the two bruchids, N. arizonensis emergence numbers are still far lower than those of A. prosopis (approximately 1:4 respectively). 5. Oviposition strategies of N. arizonensis results in high levels of egg parasitism by Uscana sp., Trichogrammatidae, that A. prosopis escapes by ovipositing in concealed places avoiding detection by parasitoids. 6. Egg parasitism is extremely high on N. arizonensis eggs (67%) and has resulted in failure by N. arizonensis to establish large populations and hence its effectiveness as a biocontrol agent is negligible. |
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