Browsing by Author "Chidawanyika, Frank"

Now showing 1 - 3 of 3
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    Biologically based methods for pest management in agriculture under changing climates : challenges and future directions
    (MDPI, 2012) Chidawanyika, Frank; Mudavanhu, Pride; Nyamukondiwa, Casper
    The current changes in global climatic regimes present a significant societal challenge, affecting in all likelihood insect physiology, biochemistry, biogeography and population dynamics. With the increasing resistance of many insect pest species to chemical insecticides and an increasing organic food market, pest control strategies are slowly shifting towards more sustainable, ecologically sound and economically viable options. Biologically based pest management strategies present such opportunities through predation or parasitism of pests and plant direct or indirect defense mechanisms that can all be important components of sustainable integrated pest management programs. Inevitably, the efficacy of biological control systems is highly dependent on natural enemy-prey interactions, which will likely be modified by changing climates. Therefore, knowledge of how insect pests and their natural enemies respond to climate variation is of fundamental importance in understanding biological insect pest management under global climate change. Here, we discuss biological control, its challenges under climate change scenarios and how increased global temperatures will require adaptive management strategies to cope with changing status of insects and their natural enemies.
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    Global climate change as a driver of bottom-up and top-down factors in agricultural landscapes and the fate of host-parasitoid interactions
    (Frontiers Media, 2019-03-28) Chidawanyika, Frank; Mudavanhu, Pride; Nyamukondiwa, Casper
    The global climate is rapidly changing and the evidence is increasingly manifesting across various biological systems. For arthropods, several studies have demonstrated how changing climates affect their distribution through phenological and physiological responses, largely focusing on various organismal fitness parameters. However, the net-effect of the changing climate among ecological communities may be mediated by the feedback pathways among interacting trophic groups under environmental change. For agroecosystems, the maintenance of the integrity of trophic interactions even under climate variability is a high priority. This is even more important in this era where there is advocacy for sustainable agriculture, with higher emphasis on environmentally benign methods. For this reason, pest management in food production systems using biological control (especially use of parasitoid antagonists) has come to the forefront. In this review, we give an overview of the diversity of physiological responses among host insect and parasitoid populations and how this may influence their interactions. We highlight how climate change may modify bottom-up and top-down factors among agroecosystems with a particular focus on plant-insect host-parasitoid tritrophic interactions. We also outline how habitat management may influence arthropod population dynamics and how it can be manipulated to improve on-farm climate resilience and parasitoid conservation. We wrap-up by highlighting how the application of knowledge of conservation biodiversity, designing of multifunctional resilient landscapes, and evolutionary physiology of arthropods under thermal stress may be used to improve the fitness of mass-reared parasitoids (in or ex situ) for the improvement in efficacy of parasitoids ecosystem services under thermally stressful environments.
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    Thermal tolerance of Cydia pomonella (Lepidoptera : Tortricidae) under ecologically relevant conditions
    (Stellenbosch : University of Stellenbosch, 2010-12) Chidawanyika, Frank; Terblanche, J. S.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Conservation Ecology and Entomology
    ENGLISH ABSTRACT: Ambient temperature plays a key role in insect-physiology, -population dynamics and ultimately -geographic distribution. Here, I investigate the survival of codling moth, Cydia pomonella (Linnaues) (Lepidoptera: Tortricidae), which is a pest of economic importance in pome fruit production, to a wide range of temperature treatments. In this thesis, I first explore how temperature affects the survival and limits to activity of codling moth and secondly investigate if thermal acclimation can improve field performance of moths used in sterile insect technique control programmes under ecologically relevant conditions. First, I found that absolute temperature as well as the duration of temperature exposure significantly affects adult C. pomonella survival. Lethal temperatures, explored between -20 °C to -5 °C and 32 °C to 47 °C over a range of durations, showed that 50% of the adult C. pomonella population killed at -12 °C and at 44 °C after 2 hrs for each treatment. At high temperatures a pretreatment at 37 °C for 1 hr dramatically improved survival at 43 °C for 2 hrs from 20% to 90% (p<0.0001). Furthermore, high temperature pre-treatments (37 °C for 1 hr) significantly improved low temperature survival at -9 °C for 2 hrs. In sum, my results suggest pronounced plasticity of acute high temperature tolerance in adult C. pomonella, but limited acute low temperature responses. Secondly, low-temperature acclimated laboratory-reared moths were recaptured in significantly higher numbers (d.f. = 2, χ2 = 53.13 p<0.001), by sex pheromone traps, under cooler conditions in the wild relative to warm-acclimated or non-acclimated moths. However, these improvements in low temperature performance in cold-acclimated moths came at a cost to performance under warmer conditions in the wild. This novel study demonstrates the importance of thermal history on C. pomonella survival and clear costs and benefits of thermal acclimation on field and laboratory performance, and thus, the potential utility of thermal pre-treatments for improved efficacy in the sterile insect technique programme for C. pomonella control under cooler, springtime conditions. Finally, on a global scale, this study highlights that low and high temperatures could play a role in CM adult survival through direct mortality and thus, may influence, or have influenced in the pest, population dynamics.