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Accueil du site → Master → Afrique du Sud → 2019 → Augmentative releases of Dactylopius austrinus De Lotto (Dactylopiidae ; Hemiptera) for biological control of Opuntia aurantiaca Lindley (Cactaceae), in South Africa

Rhodes University (2019)

Augmentative releases of Dactylopius austrinus De Lotto (Dactylopiidae ; Hemiptera) for biological control of Opuntia aurantiaca Lindley (Cactaceae), in South Africa

Mulateli, Thifhelimbilu

Titre : Augmentative releases of Dactylopius austrinus De Lotto (Dactylopiidae ; Hemiptera) for biological control of Opuntia aurantiaca Lindley (Cactaceae), in South Africa

Auteur : Mulateli, Thifhelimbilu

Université de soutenance : Rhodes University

Grade : Master of Science (MS) 2019

Résumé partiel
Opuntia aurantiaca Lindely (Cactaceae) is an invasive alien cactus which has detrimental effects on agroecosystems and indigenous biodiversity in South Africa. Dense infestations over large areas reduce grazing capacity and indigenous biodiversity. Despite the release of a biological control agent, the cochineal insect Dactylopius austrinus De Lotto (Dactylopiidae), the weed is still considered a major problem in many parts of the country. Biological control has relied heavily on classical biological control, with little augmentative biological control implemented. This study investigated the outcome of mass-rearing and augmentative releases of D. austrinus for the control of O. aurantiaca. Augmentative releases are thought to improve the level of control by increasing agent densities in the field and thus increasing the level of damage inflicted to the plants. All data were collected with the intention to optimize release strategies so that the maximum benefit from the biological control agent could be achieved. An impact study was conducted using potted plants in a greenhouse to quantify the efficacy of multiple releases of the agent on the target weed. All three of the release treatments showed consistently higher proportion of cochineal than the controls, as well as the insect exclusion treatments, and these differences were statistically significant. The number of cladodes per plant increased significantly for the insect exclusion and control treatment over the period of the study, whilst all three release treatments decreased steadily over the same period. This study indicated that the agent is damaging to O. aurantiaca and that a single release event was beneficial but that multiple releases did not result in greater levels of control. A post-release evaluation was carried out to quantify the impact of releases of D. austrinus on O. aurantiaca in the field. Plots where the agent was excluded were compared with those where the agent was left at natural field densities and three treatments where agent populations were augmented to varying degrees through releases.

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Page publiée le 20 janvier 2021