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Thesis submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfillment of the requirements for the degree PhD Science Johannesburg, September 2014 / Drought has the potential to reset trophic interactions within natural and managed ecosystems. I tested how drought stress in maize and companion plants that are used in cereal agroecosystems of Kenya affect oviposition preference, larval feeding, and development of the spotted stemborer, Chilo partellus Swinhoe (Lepidoptera: Crambidae). Five host species were tested (all Poaceae): maize (Zea mays L.), Napier grass (Pennisetum purpureum Schumach), signal grass [Brachiaria brizantha (A. Rich) Stapf], Brachiaria cv ‘Mulato’, and molasses grass [Melinis minutiflora (Beauv.)]. Under periods of water deficit, maize was oviposited on as much as under control unstressed maize in both choice and no-choice experiments. Similarly, larval leaf damage was not significantly different in drought-stressed and unstressed maize. However in Napier and signal grasses, oviposition occurred less on drought-stressed than on unstressed corresponding individuals of the same species. Oviposition acceptance and foliar damage remained low in both drought-stressed and unstressed molasses grass and Mulato. Larval survival and development remained high in drought-stressed maize, but not in Napier, signal, and molasses grass and Mulato, where survival and development were low in both drought-stressed and unstressed plants. Drought stress resulted in increased total plant volatile emission in Napier and signal grasses. This significant change in total volatile emission of the plants upon stress was not present in molasses grass, Mulato II, Silverleaf and Greenleaf Desmodium despite variable changes in the quantities and qualities of particular constituent compounds among all the plant species during water deficit. In wind tunnel bioassays, volatile organic compounds (VOCs) from irrigated Napier and signal grasses were more attractive to C. partellus than the treatment plants. However, volatiles from molasses grass, Mulato II, Silverleaf and Greenleaf Desmodium were never preferred by the gravid moths in both irrigated and drought stressed v conditions. These changes in chemical constituents of the plant VOCs also elicited behavioural responses in parasitoids. Drought-stressed Napier grass attracted gravid Cotesia sesamiae parasitoids. Other companion plant species such as molasses grass and Mulato which constitutively emit these terpenes remained attractive to the parasitoids even under periods of drought. I attribute this differential preference of the moths to the constitutive and/or induced emission of key terpenoid compounds in plants that were tested. The induction of terpenoid compounds was coupled with a reduction in the amount of green leaf volatiles such as (Z)-3-hexenyl acetate in Napier and signal grasses. Taken together, the results suggest that control of stemborer pests using stimulo-deterrent diversion tactics remains possible under periods of environmental change.

A Dissertation submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science, Johannesburg, South Africa. 2016. / Solanum mauritianum Scopoli (Solanaceae) is a perennial tree or shrub native to South America, which has become a prominent and widespread invader in numerous sub-tropical countries around the world. In South Africa, S. mauritianum is listed as one of the country’s worst ecological weeds, having been targeted for biological control efforts since 1984. Despite some constraints, biocontrol efforts have seen the successful release of two promising biocontrol agents. The first of these biocontrol agents, released against S. mauritianum, was the sap-sucking lace bug, Gargaphia decoris Drake (Hemiptera: Tingidae). Sap-feeding by G. decoris metabolically impaired the leaves, resulting in a reduction to their photosynthesis, with a greater effect on plants growing in full-sun compared to plants growing in the shade. This difference was attributed to higher leaf temperatures experienced in the sun. Herbivory reduced transpiration rates by more than 50%, resulting in a reduction in evaporative cooling of the leaf. The increased physiological damage experienced by full-sun plants may be a combination of stresses, particularly the direct effect of chlorophyll removal via herbivory and the indirect effect of accumulated heat–light stress. The flowerbud-feeding weevil, Anthonomus santacruzi Hustache (Coleoptera: Curculionidae), was released in 2008 as a biological control agent against S. mauritianum. The hypothesis that climate, particularly low temperature and low relative humidity, restricts the survival and establishment of A. santacruzi in South Africa was tested. Thermal assessments on A. santacruzi adults calculated the CTmin and LT50 as 4.1 ± 0.2 °C (n = 20) and 4.2 ± 0.3 °C (n = 90) respectively. The LH50 of A. santacruzi adults was calculated as 46.9%. The establishment of A. santacruzi at only the warm and humid release sites in South Africa advocates for the consideration of low temperature and low humidity as factors impeding the agents’ establishment and spread, particularly on the cooler and drier Highveld. Furthermore, the impact of A. santacruzi’s florivory on the reproductive output of S. mauritianum, as well as the potential of the agent to act as an indirect pollinator was assessed. Overall direct floral damage caused by A. santacruzi was trivial, with only ~5% of the anther and ~2% of the petal area being removed. However, the consequent effects of A. santacruzi were considerably more damaging, with 25% and 66% reductions in flowering and fruiting respectively. Additionally, fruits produced from inflorescences exposed to A. santacruzi were smaller in size, with fewer, less viable seeds. The feeding and presence of A. santacruzi also maintains the potential for indirect effects on the pollination of S. mauritianum. This suggests that in areas with well-established A. santacruzi populations, the weevils may simultaneously facilitate the self-pollination and potential inbreeding of S. mauritianum. Keywords: Agent impacts and effects; biological control; Bugweed; climatic unsuitability; ecophysiology; indirect effects; post-release evaluation. / LG2017

A sustainable pest control system integrates automated pest detection and recognition to evaluate the pest density using image samples taken from habitats. Novel predator/prey modelling algorithms assess control requirements for the UAV system, which is designed to deliver measured quantities of naturally beneficial predators to combat pest infestations within economically acceptable timeframes. The integrated system will reduce the damaging effect of pests in an infested habitat to an economically acceptable level without the use of chemical pesticides. Plant pest recognition and detection is vital for food security, quality of life and a stable agricultural economy. The research utilises a combination of the k-means clustering algorithm and the correspondence filter to achieve pest detection and recognition. The detection is achieved by partitioning the data space into Voronoi cells, which tends to find clusters of comparable spatial extents, thereby separating the objects (pests) from the background (pest habitat). The detection is established by extracting the variant and distinctive attributes between the pest and its habitat (leaf, stem) and using the correspondence filter to identify the plant pests to obtain correlation peak values for the different datasets. The correspondence filter can achieve rotationally invariant recognition of pests for a full 360 degrees, which proves the effectiveness of the algorithm and provides a count of the number of pests in the image. A series of models has been produced that will permit an assessment of common pest infestation problems and estimate the number of predators that are required to control the problem within a time schedule. A UAV predator deployment system has been designed. The system is offered as a replacement for chemical pesticides to improve peoples' health opportunities and the quality of food products.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains vii, 80 p. : ill. (some col.) Vita. Includes abstract. Includes bibliographical references (p. 72-76).

Revised; Originally Published: 2014 / 4 pp. / Sonic pest devices are tools that emit sound in the attempt to repel, deter, or kill unwanted animals such as insects, rodents, birds and large mammals. There are many commercially available sonic pest devices that claim to be effective.Commercially available sonic pest devices for use in residential applications have not been shown to be effective in scientific studies. For this reason, use of these devices is not advised to treat common pest problems. Although some researchers are developing sonic techniques that illustrate promise for very specific pests, these technologies are yet to be commercially available.

Antifeedants and growth regulators have potential as alternatives to conventional methods of insect pest control. As with conventional chemicals it is important to consider their effects on natural enemies of the pests. The aim of this project was to determine whether the bitter-tasting synthetic chemical denatonium benzoate as an antifeedant and compare with neem derivatives. Other aims were to investigate their effect on parasitoids and the field infestation of cabbage pests. Denatonium benzoate is systemic and had no contact effect but acted as an antifeedant on a generalist sap feeder <I>Myzus persicae</I> and reduced the survival, fecundity, and lifespan. Neem derivatives, Azatin EC and Pestistat R were more effective of which Azatin EC was the most effective. Antifeedants further reduced the fecundity and survival when parasitized with its parasitoid, <I>Aphidius matricariae</I> and neem derivatives had adverse effects on both aphid and the parasitoid. Denatonium benzoate and Pestistat R with a specialist leaf feeder, <I>Pieris brassicae</I> and all antifeedants with <I>Plutella xylostella</I> (generalist leaf feeder) and <I>Chrysodeixis eriosoma</I> (specialist brassica leaf feeder) reduced the leaf area consumed and it was inversely proportional to the concentration. The highest leaf area consumption was in denatonium benzoate and the lowest in Pestistat R. Higher azadirachtin concentrations were detrimental but denatonium benzoate was safer to the larval parasitoid, <I>Cotesia plutellae</I>. Denatonium benzoate and Azatin EC reduced field infestation of <I>M. persicae, P. xylostella</I> and <I>C. eriosoma</I> in Peradeniya, Sri Lanka and Azatin EC was the most effective. Denatonium benzoate acts as an antifeedant against cabbage pests and safer towards parasitoids hence can be used in integrated pest management programmes. Neem derivatives are comparatively more effective on pests but harmful to parasitoids. Denatonium benzoate and Azatin EC effectively reduced the pest infestation under field conditions.

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