The diamondback moth, Plutella xylostella (Linnaeus 1758.) (Lepidoptera: Plutellidae), is a major insect pest of Brassica crops in many parts of the world leading to economic losses amounting to an estimated US$ 4-5 billion. Although parasitoids (biological control agents) play a major role in suppressing the pest populations during November – May in South Africa, the pest reaches outbreak status during September and October due to low impact of parasitoids, which has necessitated regular application of insecticides. However, insecticide applications have often resulted in the pest developing resistance, and when coupled with the negative effects of several insecticides on parasitoids, integration of the two pest control strategies for effective management of P. xylostella population density has been difficult to achieve. One approach that has received little attention is integration of host plant resistance (bottom-up effect) and biological control (top-down effect) for effective management of P. xylostella. However, the interaction between host plants, the insect pest, and parasitoids is not simple and straight forward, as strong negative impact of host plants on fitness of the insect pest can be cascaded up the food chain and have a negative impact on a given parasitoid, which in turn may reduce the desired complementary effect between the two pest control strategies. To identify optimal interactions between cabbage (Brassica oleracea L. var. capitata, Brassicaceae), P. xylostella and its larval parasitoid Cotesia vestalis (Haliday 1834) (Hymenoptera: Braconidae), this study investigated (i) the effects of seven cabbage cultivars (Empowa, Hollywood F1, Megaton, Leano, Menzania, Beverley Hills and Karabo) on fitness parameters (survival, developmental time, pupal weights, longevity without food and oviposition rates) of P. xylostella; (ii) the influence of the same host plant cultivars on fitness parameters (developmental time, pupal weights, longevity xi without food, fecundity, emergence rate and sex ratio) of C. vestalis. Furthermore, net reproductive rates and the intrinsic rates of natural increase were calculated for C. vestalis that emerged from hosts fed on each of the cultivars. All experiments were conducted in climate-controlled laboratory rooms maintained at 22 ± 1 ºC (mean ± S.D.), 60 ± 5 % RH and 16L: 8D photoperiod. Under the no choice test, overall survival of P. xylostella immature stages was highest on Karabo (67.26%) and lowest on Megaton (44.92%). The larval and pupal developmental period, and generation time was prolonged on Empowa (18.48 days), Karabo (14.64 days) and Beverly Hills (17.48 days), while developmental period on Hollywood F1 (13.79 days) was shortest. Male and female P. xylostella pupal weights were lighter from larvae that fed on Megaton (4.13 and 4.65 mg), Menzania (4.53 and 4.91 mg), and Hollywood F1 (4.11 and 5.08 mg), whereas pupal weights from Karabo (6.0 and 6.82 mg) were the heaviest. Unfed female moths originally reared on Beverley Hills had the highest longevity (5.05 days), whereas those reared on Leano (3.54 days) and Megaton (3.89 days) had the shortest life span. Under the choice-test, P. xylostella moth laid significantly more eggs on Empowa (48.8%) and Hollywood F1 (45.6%) and least on Menzania (11.8%) and Leano (10.6%). Megaton was more resistant to P. xylostella due to lower survival rates of immature stages, lower pupal weights and moth longevity. The generation time of C. vestalis was shortest on Karabo (10.10 days) and Leano (10.38 days), and longest on Megaton (12.57 days) and Empowa (12.80 days). The highest pupal weight of C. vestalis was obtained from parasitoids reared from P. xylostella fed Menzania (5.4 mg), Megaton (5.25 mg) and Beverly Hills (4.85 mg) and the lightest on Karabo (3.8 mg). Parasitoids reared on larvae that fed on Hollywood F1 lived the longest (2.28 days) followed by Menzania (1.94 days) and Beverly Hills (1.8 days), whereas those whose hosts fed on Leano had shortest life span (0.83 days). Despite the parasitoids from Megaton hosts being heavier, their fecundity and number of female progeny per female (16.87 and 3.60, respectively) were lowest. Cotesia vestalis fecundity and daughters produced per female were highest on hosts fed on Menzania (38.00 and 9.13, respectively) and Beverly Hills (32.87 and 9.07, respectively). As a consequence, the net reproductive rate (R0) and intrinsic rate of increase (r) were higher on Menzania (7.87 and 0.58, respectively) and Beverly Hills (8.29 and 0.62, respectively). As survival and overall fitness of P. xylostella was lower on Megaton, this cultivar can play a major role in restricting population growth of this pest and thus generational number of eggs deposited on it during September and October. However, this strong bottom-up effect of Megaton on P. xylostella was cascaded up the food chain, as overall fitness of C. vestalis was lower on hosts developing on it. In contrast, the overall fitness of C. vestalis was higher on hosts that developed on Menzania and Beverly Hills. As these cultivars showed potential to sustain population density of C. vestalis at higher levels, it is also assumed that the period required for the parasitoid to reach the critical density to suppress the host population at a lower average density will be reached quicker than on other cultivars. Thus, their cultivation may improve biological control of P. xylostella during November–May in South Africa / Agriculture, Animal Health and Human Ecology / M. Sc. (Agriculture)

The interaction between farmers, agricultural scientists and extension workers is sometimes overlooked in agricultural entomology. In an attempt to respond to this reality this study examines some foundation of this interaction in relation to the pest management practices of subsistence and small-scale farmers and also highlights the problems that might arise in the implementation of IPM. Problems involving pests occurrence; language barriers; beliefs, knowledge and perception about insects, and visual literacy are examined. The thesis has a two-fold focus, firstly the study of pests on cabbages of subsistence farmers in Grahamstown and secondly a broader focus on other aspects such as cultural entomology, perception of insects and visual literacy specifically in relation to Xhosa speaking people in the Eastern Cape. The most important crop for emergent farmers in the Eastern Cape are cabbages, which have a variety of pests of which diamondback moths and are the most important. Traditional pest management practices tend to influence the development of IPM programmes adopted by these farmers. Eastern Cape farmers apply periodic cropping systems, which had an effect on the population densities of diamondback moth (DBM), other lepidopteran pests and their parasitoids. Considering the maximum population densities of DBM, which were 0.2 - 2.9 larvae/plant, there were no major pest problems. The availability of parasitoids, even in highly disturbed and patchy environments, showed good potential for biological control. Since some extension officers cannot speak the local farmers’ language, a dictionary of insect names was formulated in their language (isiXhosa) to assist communication. Response-frequency distribution analysis showed that the dictionary is essentially complete. The literal translations of some names show that isiXhosa speakers often relate insects to people, or to their habitat or classify them according to their behaviour. Farmers from eight sites in the Eastern Cape were interviewed regarding their knowledge and perception of insect pests and their control thereof. To some extent, farmers still rely on cultural control and have beliefs about insects that reflected both reality and superstition. There is no difference between the Ciskei and Transkei regions regarding insect-related beliefs. Farmers generally lack an understanding of insect ecology. There is a need for farmers to be taught about insects to assist with the implementation of IPM. Leftover pesticides from commercial farms or detergents are sometimes used to manage the pests. When training illiterate or semi-literate farmers, it is important to understand their media literacy so as to design useful graphic and object training media. Generally farmers showed that they either understand graphic or object media depending on the features of the insects being looked at. These findings are discussed with regard to the potential development of IPM training material for subsistence and small-scale farmers in a community.

PhD (Agric) (Plant Production) / Department of Plant Production / Brassicas are important vegetable crops grown for home consumption and market gardening in eastern and southern Africa. However, productivity is affected by aphids, through both direct feeding and disease transmission. Botanical insecticides have potential to control the aphids, but so far few plants have been evaluated for use on brassicas. This study was conducted to evaluate the effectiveness of Solanum panduriforme to control aphids on brassicas. Botanical extracts from three parts of S. panduriforme were assessed for their insecticidal effects on the cabbage aphid, Brevicoryne brassicae. The extracts from leaf powder (LP), ripe berry powder (BP), fresh ripe berries (RB) and fresh unripe berries (UB) were extracted with four solvents; water, ethanol, hexane and diethyl ether, using homogenisation, maceration and solvent-assisted / sequential extraction methods. The effectiveness of the extracts was determined by laboratory bioassays as well as by plant assays in the screen house and under field conditions. The experiments were replicated three or four times depending on the assays and the design used was completely randomized design (CRD). The immature (LP and UB) plant parts were generally more effective than the mature (BP and RB) plant parts, with mortalities ranging from 100 % down to 40 % respectively depending on assays. Ethanol extracts were more effective than aqueous extracts (LP 96% and 63%; BP 96% and 64%; RB 100% and 64%; UB 100% and 90%). The dried crude extracts from hexane were more effective than di-ethyl ether extracts. The group chemical analysis indicated presence of alkaloids in the berries (BP, RB and UB), which were absent in the leaves (LP). Phenolic compounds and flavonoids were present in all the extracts (LP, BP, RB, and UB). Saponins were present in the fresh parts (RB and UB). The results show how the locally available S. panduriforme plants can be used as an aphicide to control aphids on brassicas. Farmers can directly prepare an easy and cheap botanical / NRF

The seasonal abundance of the imported cabbageworm, <i>Artogeia rapae</i> (L.)), cabbage looper <i>Trichoplusia ni</i> (Hubner)) and diamondback moth (<i>Plutella xylostella</i> (L.)) was determined in 1982 to 1984 on cabbage in southwest Virginia. The imported cabbageworm was the most important pest. It had one and a partial second generation in 1982 and 1983, and two and a partial third generation in 1984. Market Prize and Green Winter varieties had lower <i>A. rapae</i> infestations than Abbott & Cobb #5 or Rio Verde. Two generations of the diamondback moth, which preferentially fed on cabbage leaves versus heads, were seen in 1983 and 1984. <i>Diadegma insularis</i> (Meus.) (Hymenoptera: Ichneumonidae) parasitized 46% and 69% of the diamondback moth in 1983 and 1984, respectively. Higher parasitization of <i>P. xylostella</i> was found in pupae collected from Abbott & Cobb #5. Two generations of the cabbage looper were seen in 1983 and a single generation in 1984. <i>Pteromalus puparum</i> (L.) (Hymenoptera: Pteromalidae) parasitized 64.1% and 32.5% of imported cabbageworm pupae in 1983 and 1984; parasitism was most pronounced in the latter part of the season. High percentages of parasites successfully emerged as adults, indicating efficient host utilization. Most parasite mortality within the host occurred in the larval stage; mean adult parasite emergence per host for 1983 and 1984 was 52.3 with a 1:1 sex ratio. <i>P. puparum</i> parasitized either host sex, producing equal proportions of male and female parasites. Adult female <i>P. puparum</i> were not adversely affected by residues of methomyl (Lannate®), permethrin (Pounce®) and fenvalarate (Pydrin®), but males showed significantly higher mortality than controls following exposure to methomyl after 12 h, and methomyl and permethrin after six days. <P. puparum</i> adults were successfully refrigerated for up to 15 days at 3°C in individual gelatin capsules. Survival beyond 15 days was better at l5°C and 23°C. <i>A. rapae</i> larvae could be reared at densities of 30 to 60 larvae per 70±10 g on a high wheat germ artificial diet. Pupae from the lowest density were larger in length and weight than those reared at the two higher densities, and all laboratory-reared pupae were smaller than either normal or parasitized field pupae. / Ph. D.