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This study focuses on the effective biocontrol agent Chilocorus nigritus (Fabricius). Its behaviour and ecology were compared with other Chilocorus spp. where appropriate, to elucidate why this species is such an effective biocontrol agent, and how to improve methodology for its deployment as a natural enemy. An artificial diet for C. nigritus was developed, but was still sub-optimal. Asterolecanium miliaris (Boisduval) was a suitable prey for all life stages of C. nigritus and the adults of Chilocorus bipustulatus (Linnaeus) and Chilocorus infernalis Mulsant, but was inadequate for larvae of the last two species. Adult weight, measured at one day after adult eclosion, was an appropriate indicator of the effects of larval treatment on their development and on the fitness of subsequent adults. There was no improvement in culture vigour due to a behavioural response of individuals within one generation to fluctuating as opposed to constant temperature. starvation for between 10h and 24h was appropriate for standardisation of hunger. Measuring feeding rate at a range of static temperatures did not reflect differences in the climatic adaptations of six Chilocorus spp., but mortality rates at increasingly high temperatures were useful. Chilocorus spp. showed little ability to choose between prey species. Prey substitutions adversely affected adults and larvae. Introduction of adults was the most effective method for field establishment. Giant bamboo Dendrocalamus giganteus Munro was a valuable site for field releases of C. nigritus, but less useful for C. bipustulatus and C. infernalis. Counter to assumptions on which interference models have been based, no significant intraspecific interference, reducing predatory efficiency, was observed. Visually prominent features on the horizon and a specific leaf shape, were attractive to foraging C. nigritus. The location of prey patches by adults was facilitated by prey odour, but not so for larvae. Adults detected individual prey olfactorily and visually over short distances, but physical contact was required for detection by larvae. Prey location by larvae and adults was facilitated by alterations in movement patterns in response to prey consumption. Differences in prey detection and the effects of prey substitutions, between the life stages, were related to field behaviour. The relevance to biological control, of responses to rearing conditions and feeding and foraging behaviour, was investigated. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.

The Russian wheat aphid, Diuraphis noxia is one of the most destructive exotic invaders of South Africa, capable of reducing individual wheat plant yields by up to 90%. Entomopathogenic fungi are important natural mortality factors associated with this aphid in its Eurasian endemic habitats as well as in the United States and Canada; their impact often exceeding that of predators and parasitoids. The principal objectives of this study included (1) baseline characterization of the aphid-pathogenic flora associated with aphids from South Africa, with special reference to six common cereal aphids, (2) quantification of the comparative impact of the different fungal species on the cereal-aphid complex in three different wheat producing regions of South Africa, (3) field evaluation of the Hyphomycete Beauveria bassiana against D. noxia on resistant wheat, (4) screening of six fungicides for their potential usage in managing entomophthoralean epizootics within greenhouse rearings of the Russian wheat aphid, and (5) development and evaluation of a novel bioassay protocol for screening entomopathogenic Hyphomycetes against D. noxia. A total of nine species of fungi known to infect and kill aphid hosts were collected, including the six entomophthoraleans, Pandora neoaphidis, Conidiobolus thromboides, Conidiobolus obscurus, Entomophthora planchoniana, Conidiobolus coronatus and Neozygites fresenii, and three Hyphomycetes, Beauveria bassiana, Verticillium lecanii, and Paecilomyces farinosus. The former four entomophthoraleans are considered first reports from this country. For the first time, morphological characteristics of these nine South African-collected species are visually depicted and techniques for their isolation and in vitro culture discussed. Seven species of fungi were recorded from D. noxia, of which P. neoaphidis was the most important, causing up to 50% mortality during the late season under dryland conditions in the summer-rainfall region. Mycoses at epizootic levels, together with the large diversity of fungal species recorded from this host, indicated a high level of susceptibility to fungal infection. In contrast, infection of the oat aphid Rhopalosiphum padi remained < 5% despite favourable numbers of hosts and apparently suitable environmental conditions. This phenomenon strongly suggests some level of low susceptibility to fungal infection in this species. Under irrigated conditions m KwaZulu-Natal, the rose-gram aphid Metopolophium dirhodum was the predominant aphid but remained below economical injury levels. Field surveys revealed that this aphid was effectively targeted by P. neoaphidis and C. obscurus, and findings suggest that in some areas of South Africa entomophthoralean fungi effectively suppress this aphid, negating the need for insecticide applications. On average, ca. 61% control of D. noxia on resistant wheat was observed following an application of B. bassiana (5 x 10¹³ conidia per hectare) during the early flag-leaf stage of the wheat. Efficacy of B. bassiana applications on younger plants appeared to be influenced by the level of aphid activity, possibly explained by secondary pick-up of inoculum by D. noxia. These findings accentuate the importance of understanding the tritrophic relationship between host plant, pest and pathogen. The fungicides copper oxychloride, mancozeb + oxadixyl, captab + metalaxyl, bittertanol, iprodione, and mancozeb at a rate of 0.1% active ingredient moderately to strongly inhibited C. thromboides vegetative growth (mean inhibition 81.1 %). Mancozeb at concentrations of 10.0, 2.0, 1.25, 0.5, 0.08, and 0.016% was further evaluated in vitro. The fungus growth cut-off point, midway between 1.25 and 2.0% mancozeb, was calculated and a rate of 1.625% active ingredient per litre of water was used to decontaminate the fungus-infected D. noxia cultures. A novel bioassay protocol was developed, employing live host plants for rearing aphids post inoculation. Using this design against D. noxia, an average LC₅₀ estimate of 85 conidia per mm² for B. bassiana strain GHA was calculated. Control mortality was restricted to levels below 4%. The data indicated high precision due to an average coefficient of variation for slope of less than 20%, and an average chi-squared value of 5.46 ± 2.74 (n = 10 assays). The design will accommodate the use of cereal aphid species other than D. noxia, while live host plants will facilitate tritrophic studies on the effect of host-plant resistance on fungus-induced mortality of D. noxia. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2002.

This study investigated effects of insect growth regulators (IGRs), recommended for use on citrus in southern Africa, on non-target organisms, particularly species of Coccinellidae in and around three citrus estates in the lowveld region of Swaziland, i.e. Tambuti, Tambankulu and Tunzini estates. Some of the species are important predators of citrus pest insects. The distribution of coccinellids within an agricultural land mosaic and factors affecting this distribution pattern were also investigated. Results showed that coccinellid densities and species diversity were lowest in the natural veld surrounding the orchards. In contrast, citrus orchards had the highest coccinellid densities and diversity. River borders, along the Great Usuthu river, had intermediate densities and diversity. While temperature, relative humidity and ground insolation had no significant effect on coccinellid population densities, the presence / absence of prey (host plant), on the other hand, was an important factor. This was the case both for phytophagous and predatory coccinellid species. These showed close patterns of distribution with their respective host plants or prey species. Economically important species, such as Rodolia spp., were restricted to the orchards, while other species, especially those whose economic role is uncertain, such as Cheilomenes lunata and Scymnus spp., were found in most habitat types. Coccinellid population densities were assessed during four treatment programmes: 1) an integrated pest management (IPM) programme where no IGRs were used, 2) a programme where any of the recommended IGRs were to be applied, 3) conventional pesticide programme, and 4) an orchard which did not receive any chemically treatment over the last four years (at Tambankulu estate only). Significant differences between treatment programmes were observed at all three estates, when only economically important coccinellid species were assessed. Orchards under an IPM programme (with no IGRs) were found to have significantly higher population densities compared to those in IGR-treated or under a conventional pesticide regime. The untreated orchard at Tambankulu, however, had significantly higher coccinellid densities of economically important species and higher overall population densities than any of the managed orchards. Of the three estates assessed, Tunzini had significantly higher population densities of all beneficial coccinellids, (excluding the untreated orchard at Tambankulu). Natural vegetation around Tunzini and Tambuti contributed to the higher coccinellid densities compared to Tambankulu, which was surrounded by other agricultural land. Laboratory and field experiments on two non-target species, the ladybird Chilocorus nigritus (Fabricius) (all stages) and the moth Bombyx mori (Linnaeus) (larval stage) assessed specific IGR effects, if any. Three IGRs, buprofezin, teflubenzuron (both chitin synthesis inhibitors) and pyriproxyfen (a juvenile hormone analogue) were used. All three pesticides are currently recommended for use on citrus in southern Africa and were tested at the recommended dosages. Laboratory experiments showed that all three IGRs have a negative impact on both non-target species. When B. mori received direct applications, there was larval mortality as a result of the failing to complete moulting or dying immediately after moulting. In addition, no larvae were able to pupate after having fed on contaminated leaves. In the case of C. nigritus, larvae fed IGR-treated scale or sprayed with buprofezin suffered significantly higher mortality than controls, while IGR effects on those sprayed with, or fed scale-treated with, pyriproxyfen or teflubenzuron were not significant. No adults however, emerged from any pupae in any of the treatment groups. All three IGRs had ovicidal activity on C.nigritus eggs. Adult fecundity in both field and laboratory experiments was not affected significantly after exposure to any of the three IGRs. In field experiments, the proportion of larvae of the moth and ladybird that developed up to the reproductive adult stage, after exposure to buprofezin, was not significantly different from the control. This was not the case for pyriproxyfen and teflubenzuron. Buprofezin was therefore found to be the least detrimental of the three IGRs tested. Minimal drift was observed when a knapsack sprayer was used. However, there was spray drift up to 32m (the furthest distance assessed here) where commercial sprayers were used. This suggests that pesticide drift from orchards to adjacent areas would have serious implications for biological diversity in the river borders and rivers adjacent to the estates. The sensitivity of the non-target species to the IGRs tested needs serious consideration, as it indicates a broader spectrum of activity for the compounds than what is promoted. Additionally, natural control may be affected. This is because the timing of IGR applications and increasing coccinellid populations coincide, resulting in a reduced pool of coccinellid predators. This study emphasised the importance of an appropriately heterogenous landscape to maximise habitat availability for the coccinellids. Although the economic role of the multihabitat coccinellid species recorded here is unknown, they nevertheless clearly contribute to citrus pest control. Such a mosaic landscape, in conjunction with IPM, with no IGR use, promotes ecological diversity and controls pests with minimum disruption to biodiversity. The use of IGRs in citrus thus needs carefiil reconsideration in light of the non-target effects observed on the two species, especially the valuable predatory species, C. nigritus. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1998.