Browsing by Author "Faure, Sariana"

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    Development of a habitat management plan for improving the biological control of the vine mealybug planococccus ficus (signoret) in vineyards
    (Stellenbosch : Stellenbosch Univerisity, 2015-03) Faure, Sariana; Addison, Pia; Veldtman, Ruan; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH SUMMARY: The vine mealybug, Planococcus ficus (Signoret) is a major, cosmopolitan pest in all regions where grapes are grown. Vine mealybug has a direct injurious effect on vines through feeding, produces honeydew, on which sooty mould develops and has been shown to be a vector of the grapevine leafroll virus and associated closteroviruses. This project entailed research on the parasitoids of P. ficus, mainly Coccidoxenoides perminutus (Timberlake). The aim of this work was to contribute basic biological information for the establishment of a habitat management plan in vineyards to improve biocontrol of P. ficus. Two surveys were conducted to determine, firstly, the occurrence of mealybug parasitoids in the vineyards and their associated natural habitats, and secondly the association between flowering plants and parasitoids close to vineyards. Olfactometer screenings were conducted to determine attractiveness of six plants as food sources for adult C. perminutus. A comprehensive life history experiment was initiated to be compared with previous findings. In the first survey, to assess the biodiversity of mealybug parasitoids in vineyards and their associated natural habitats, C. perminutus, Anagyrus sp. near pseudococci (Girault) and Leptomastix dactylopii (Howard) were the predominant parasitoids found between January and May, with a peak in abundance during February. Signficantly more parasitoids were found in vineyards compared to associated natural habitats (p=0.049). The survey further indicated that these parasitoids, being density-independent and therefore not in need of high pest populations to sustain numbers, could contribute to integrated pest management, and with effective habitat modifications, their numbers could be naturally boosted to lend a valuable eco-system service. In the second survey, to determine whether parasitoids occur in the field in flowering plants associated with vineyards, a total of 20 indivdual parasitoids from 16 species were found. This is a promising indication that, although their impact on P.ficus was not measured during this study, the correct flowering plants interplanted in vineyards or on the edges could have a positive effect on the necessary occurrence of mealybug parasitoids as well as other natural enemies and pests in vineyards. Attractiveness of plants for C. perminutus was determined through the screening of a variety of flowering plants with a four-armed Pettersson olfactometer. Of the six plants tested, only Euryops abrotanifolia (L.) DC had a significant attractant effect (p=0.003926) on C. perminutus. The population of the parasitoid could possibly be increased by planting this plant in or around vineyards to provide a food source, and it is recommended that this plant be further investigated as a parasitoid attractant in the field. Furthermore, more plants need to be tested for inclusion in habitat management, as it is likely that a combination of plants will be more effective for biological control. To determine life table parameters of C. perminutus, including adult fitness and larval host preferences, laboratory experiments were conducted at 25°C on Planococcus citri (Risso), as initial experiments utilizing P. ficus had failed. In constrast with previous studies where the second and third nymphal instars were parasitised, all nymphal instars were attacked in this study, with no significant difference between them (p=0.057). Cost of life when laying eggs or not also came to no significant difference (p=0.46252). Lifetable parameters (Ro=159.5; T=27.602; rm=0.511) were different to those determined by Walton (2003) (Ro=69.94; T=29.5; rm=0.149) except for T which was similar, although the latter study was conducted on P. ficus. These differences could also be attributed to the use of mummies instead of hatched parasitoids, when collecting progeny for the determination of the preferences and parameters. Information obtained through these above mentioned experiments should be of use to rearing facilities and contribute to the establishment of a habitat management plan in vineyards to improve the control of P. ficus.