Doctoral Degrees (Conservation Ecology and Entomology)

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Browsing Doctoral Degrees (Conservation Ecology and Entomology) by browse.metadata.advisor "Barnes, B. N."

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    Development of an integrated pest management system for vine mealybug, Planococcus ficus (Signoret), in vineyards in the Western Cape Province, South Africa
    (Stellenbosch : Stellenbosch University, 2003-03) Walton, Vaughn M. (Vaughn Martin); Pringle, K. L.; Barnes, B. N.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: A survey was conducted in the Western Cape Province during the 1999/2000 and 2000/2001 seasons on mealybugs occurring in vineyards. P/anococcus ficus (Signoret) was the dominant mealybug in vineyards during this time. During this study P. ficus was recorded for the first time on roots of grapevines, which has far reaching implications for the control of this important vine leafroll virus vector as control actions were focused on above ground control. Other mealybugs presently recorded in local vineyards included Pseudococcus /ongispinus (Targioni) and Ferrisia ma/vastra (McDaniel). Pseudococcus viburni (Maskell) and Ps. so/ani Ferris were found on weeds in vineyards. Natural enemies of P. ficus recorded most frequently were species of Nephus predatory beetles, and the parasitaids Coccidoxenoides peregrinus (Timberlake), Anagyrus sp. and Leptomastix dacty/opii (Howard). Developmental studies on P. ficus and C. peregrinus indicated that the intrinsic rate of increase (rm) was similar, peaking at 25°C (rm = 0.169 for P. ficus; rm = 0.149 for C. peregrinus). The net replacement rate (Ra) was higher for P. ficus than for C. peregrinus at all five temperatures tested. The Ra for P. ficus reached a maximum at 21°C (308.87) and C. peregrinus at 25°C for C. peregrinus (69.94). The lower and upper thresholds for development of P. ficus were estimated at 16.59 and 35.61°C respectively. The lower threshold for development of C. peregrinus was 8.85°C. These parameters indicated that both insects were well adapted to temperatures in the Western Cape Province. The lower minimum threshold temperature of C. peregrinus in relation to that of P. ficus suggests that C. peregrinus should be more active during winter and early spring than P. ficus. A central systematic presence-absence sampling system was developed for P. ficus. Monitoring three different plant parts on the vine indicated that new growth areas on vines adjacent to the main stem could serve as an early warning system for pending P. ficus bunch infestations. Intervention should be planned when 2 % of the stems are infested with P. ficus when using this system. Seasonal population studies of P. ficus and its natural enemies showed that stem infestation by P. ficus reached peak levels during January in Robertson and Stellenbosch and during February in the Hex River Valley. Vine mealybugs colonised new growth early in the season, followed by the leaves and eventually the bunches towards the end of the season. High stem infestations early in the season resulted in high bunch infestation levels at harvest. A density dependent relationship was evident between P. ficus populations and parasitoid populations, suggesting that the parasitoids played a mayor role in the biological control of P. ficus populations. Biological control was however only achieved towards the end of the season when damage to the crop had already occurred. Mass releases of C. peregrinus on P. ficus populations were done in order to augment biological control as an alternative to chemical control. Between five and six releases of 20 000 C. peregrinus per release were done at monthly intervals in three grapegrowing areas. Mass released C. peregrinus controlled P. ficus adequately in the Hex River Valley. Control of P. ficus using this approach was no worse than using chemical control in Robertson and Stellenbosch. C. peregrinus is commercially available and can therefore be used as an alternative to chemical control by producers. Degree day estimation was used to predict development of P. ficus populations. This information was used as an input in a P. ficus pest management model. Data acquired from P. ficus and ant monitoring were used as components to construct a decision chart. This chart can be used by producers to optimise the control of P. ficus populations using either chemical control or mass releases of C. peregrinus.