[Introduction] In the Western Cape Province the mealybug, Planococcus citri (Risso), was first reported on vines in 1930 by Joubert (1943a). By 1935 this mealybug had spread to the Hex River Valley, and subsequently to all the main table grape producing areas of the Western Cape Province. At present Pl. citri is the most important insect pest of the table grape industry and can, if not effectively controlled, result in a loss of at least five per cent of the export table grape crop (Kriegler, 1954). Some preliminary work on the natural enemies of Pl. citri on vines was carried out by Stubbings in 1948, but no further work of this nature has been undertaken in this area since then. The fact that the natural enemies can be an effective check to this mealybug on vines in the Western Cape Province has been known for a number of years (Potgieter, 1937; Hattingh, 1943; Joubert, 1943a; Myburgh, 1951). The present work is an attempt to obtain some basic knowlege of the population fluctuations of the insects concerned in this biological control. Surveys undertaken have shown that there is a complex of primary, secondary and possibly tertiary Hynenopterous parasites associated with Pl. citri. The presence of hyperparasites reduces the efficiency of the primary parasitic Hymenoptera. The usefulness of these primary parasites is further reduced as they only occur in effective numbers for a short period of the year. On the other hand, although attacked by some parasites, the numerous coccinellids found preying on Pl. citri are of more importance in reducing the mealybug populations, as they are present on the vines in effective numbers for the greater part of the year.

Phthorimaea operculella, commonly known as the Potato Tuber Moth, is an economically important agricultural pest worldwide. The baculovirus, Phthorimaea operculella granulovirus (PhoGV) has been considered as a means of control alternative to chemical control because of its host specificity and harmless impact on other organisms and ecosystems. An isolate of PhoGV obtained from a South African PTM population would be beneficial in the production of a biopesticide, which is not yet available. An efficient and cost-effective rearing method would be advantageous for potential commercial production. Commercial table and seed potato plantations and storage facilities located in Patensie, Bathurst, Howick and Ivanhoe were surveyed for PTM infestations. Patensie was the only site where milky discoloured larvae were found, a potential symptom of PhoGV infection. TEM analysis revealed no virus in these samples. Since no virus was found in the field-collected samples, PTM insects were collected to initiate rearing in the laboratory. PTM was raised by three different methods in the laboratory. A cost/benefit analysis, survival rate, fertility and sex ratio were recorded for each rearing method. Rearing method one was deemed unsuccessful for efficient commercial rearing, as survival percentage and fertility were low. Rearing methods two and three had high survival rates and high fertility, and were efficient and less labour intensive than rearing method one. Rearing method three was the most productive technique, but for commercial production rearing method two was considered the most manageable and efficient. The sex ratio was 1:1 for all three cultures. The cost analysis revealed that rearing methods two and three were less expensive than rearing method one because less labour was required to monitor insects. The success of rearing PTM for 19 months will enable these cultures to be up-scaled to a large production facility for mass rearing. Virus was not found in the field surveys or in laboratory cultures, therefore chemical, temperature, humidity and carbon dioxide stressors were used in an attempt to initiate a baculoviral infection. Symptoms were exhibited in larvae subjected to chemical, temperature and humidity treatments, but these were confirmed by TEM analysis not to be a result of PhoGV infection. The success of rearing PTM in the laboratory suggests that the method could be used in the commercial rearing of the insects in a large mass-rearing facility. The data obtained from induction protocols have allowed for better understanding for future induction for PhoGV and other baculoviruses in other insect species. The failure to isolate a South African PhoGV strain for developing a biopesticide against PTM has motivated further studies in obtaining a baculovirus in order for South Africa to develop a commercial product against this pest.

The gregarious pupal endoparasitoid, Tetrastichus howardi Olliff (Hymenoptera: Eulophidae), was introduced into South Africa as a biocontrol agent against the maize and the sorghum stem borers, Busseola fusca Fuller and Chilo partellus Swinhoe. Preovipositional behaviour, ovipositional behaviour, development, fertility, sex-ratio, and longevity were studied in the laboratory. A complex courtship behaviour was observed, however 35.3% of females were mated before emergence from the host pupa. Preoviposition period ranged from 100 mins up to 5 days. Host searching time in Petri dishes was shorter for lepidopteran pupae than for their parasitoid pupae, and shortest when T. howardi had previously experienced the host. Duration of oviposition was significantly longer in the lepidopteran pupae than in the smaller tachinid puparia. T. howardi showed no difference in preference for hosts of different ages. The lepidopteran hosts were preferred to their parasitoids. If T. howardi had previously experienced a certain host its pereference for that host tended to increase, but not significantly. When reared on a certain host, the preference for that host did increase. The parasitoid was able to discriminate between parasitzed and unparasitzed pupae although this ability developed only 2 days after the pupa was parasitized. Cotesia sesamiae Cameron, the main indigenous parasitoid of B. fusca and C. partellus, was not attacked by T howardi. The total duration of development from egg deposition to the adult stage ranged from 18 to 26 days at 24°C and 60% RH. Emergence of adults began after first light, mean emergence time in winter being 09h00. Emergence rate of T. howardi from parasitized hosts, and mortality rate of parasitized hosts, was higher for C. partellus and H. armigera than for Eldana saccharina Walker and Palexorista laxa Curran. This decreased for C. partellus and H. armigera when superparasitized. A strong correlation existed between total parasitoids emerging from a host and percentage of females. When a lepidopteran pupa was parasitized by a single T. howardi female, 55 progeny emerged of which 94% were females. Larger females showed greater fertility and also produced a higher percentage of females. Younger hosts were more suitable for development of T. howardi. Females lived for 5.4 to 52.5 days, and males lived for 3.1 to 28.6 days, depending on presence or absence of food, water and hosts. Reasons for releasing T. howardi in the field are discussed. Only 2 recoveries of parasitized C. partellus pupae were made from the field.

The commercial forest industry in South Africa is predominantly dependent on large tracts of exotic monoculture plantations. While this simplifies management practice, there is always the inherent danger posed by introduced pests and diseases. Classical biological control is usually the most effective control method against introduced exotic pests. Climatic factors and seasonal differences may negatively affect the ability of the natural enemies to establish successfully at the new location. Successful establishment of the natural enemies usually results in control over the pest within four years. Sirex noctilio naturally occurs in the mediterranean countries of Europe and North Africa. It is the only member of the Siricid family capable of killing living pine trees. Sirex noctilio was accidentally introduced into New Zealand from Europe during the early 1900s. It has since been found in Australia, Brazil, Argentina South Africa and Chile. Initial biological control in New Zealand and Tasmania was through the release of Siricid specific parasitoid wasps from Europe and North America. The discovery of the accidental introduction of the entomophagous nematode Beddingia siricidicola and its subsequent artificial culturing for release provided the platform for the biological control methodology, which brought the Sirex woodwasp under control. The methods and natural enemies used in New Zealand and Australia were introduced by the South American countries and in the Western Cape of South Africa. Successful biological control was achieved in the Western Cape within two years after the initial introduction of the nematode B. siricidicola. The migration of S. noctilio into the summer rainfall regions of South Africa occurred in the absence of the associated natural enemies. This resulted in rapid population growth of the pest and substantial damage was caused to plantations of Pinus patula in the Eastern Cape and KwaZulu-Natal. Initial attempts at introducing B. siricidicola during 2004 were not very successful. This study contributes to the understanding and adaptation of the biological control methods to the summer rainfall climate. The key finding was that in the summer rainfall climate, only the bottom third of nematode inoculated S. noctilio infested trees produced parasitized adults during the emergence period. A comparative study was done on log samples from S. noctilio infested trees collected in the Western Cape and KwaZulu-Natal. iv An adapted nematode inoculation technique for pulpwood plantations in the summer rainfall regions was developed and implemented in mass inoculations with B. siricidicola during 2007 and 2008. Locally available herbicides were tested for suitability of use in the establishment of trap trees, which would attract ovipositing S. noctilio females in situations where low numbers of the woodwasp occur. Determination of the levels of natural B. siricidicola parasitism in S. noctilio adults during the 2008 emergence period indicate successful establishment of the nematode in KwaZulu-Natal. Successful introduction of the parasitoid wasp Ibalia leucospoides into the summer rainfall regions has also been achieved.

Sclerotinia homoeocarpa F.T. Bennett, causal agent of dollar spot on creeping bentgrass (Agrostis palustris Huds.); and Rhizoctonia solani Kihn, causal agent of brown patch on tall fescue (Festuca arundinacea Schreb.), are important pathogens of turfgrass. This research evaluated the ability of twenty bacterial strains of the genus Pseudomonas as potential biological agents for the control of these diseases. Year 1 dollar spot field trials resulted in the identification of five strains performing statistically as well as the recommended fungicide, chlorothalonil. Year 2 trials, using the top strains from Year 1, employed different application schedules and inclusion of a commercial spray adjuvant, Agri-Dex™, Results from Year 2 dollar spot trials indicated that eight strains performed statistically better than the non-treated control. Results from Year 1 and Year 2 of brown patch field trials provided three strains that performed statistically better than the nontreated control during Year 1, but only one strain during Year 2. Laboratory tests performed with all strains and both pathogens showed that demonstration of agar-based inhibition is more difficult to obtain with R. solani. Six strains evaluated using AgriDex™ and S. homoeocarpa in laboratory and greenhouse tests, determined that application with Agri-Dex™ can be more effective than with bacteria alone. Supporting greenhouse tests using the top strains from the S. homoeocarpa field trials to evaluate application timing in controlling dollar spot, indicated less disease with earlier and more frequent applications. With further research, several strains have the potential for disease control on turf, particularly dollar spot, and may reduce the reliance on chemical fungicides. / Master of Science

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Graduation date: 1995

In the agricultural muck soil area of southwestern Quebec, two native parasitoids, Peristenus pallipes and P. pseudopallipes (Hymenoptera: Braconidae) were found to parasitize nymphs of the tarnished plant bug Lygus lineolaris (Hemiptera: Miridae), on various flowering plants and on cultivated lettuce. Parasitism levels (ranging from 1.3% to 92.3%) varied with host plant species sampled, and with methods used for the calculation of percentage parasitism. The percentage parasitism of tarnished plant bug populations was expressed as pooled values from all samples in the season (method 1), and by the Southwood and Jepson's graphical method (method 2). Phenology of parasitism, defined as the time during which female parasitoids are active in the field, was evaluated for both native parasitoid species. The cold-hardiness of P. digoneutis, a European nymph parasitoid introduced in northern United States, was evaluated in the laboratory by measuring the supercooling point and cumulative cold damage at sub-zero temperatures. When compared to the native P. pallipes and P. pseudopallipes the exotic parasitoid showed the same capacity to withstand cold temperatures. Prior to introduction, the evaluation of the impact of P. digoneutis on indigenous species will require a rapid identification to species level. The development of immature stages of P. digoneutis was studied to find taxonomic and developmental differences between the three species. At $21 pm1 sp circ$C, the egg matures in five days, and there are three larval instars, the first two molting inside the host while the third emerges from the host, three to four weeks after egg deposition. Adult characters of the pre-imaginal stage can be used to distinguish the exotic P. digoneutis from the two native species since mouth sclerites of the final instar larvae of P. digoneutis, P. pallipes and P. pseudopallipes do not possess reliable distinguishing characters. (Abstract shortened by UMI.)