Abstract
Biological control is a longstanding approach in the management of populations of pests, vectors and invasive species. Mosquitoes are major vectors of pathogens and parasites which induce unrivaled morbidity and mortality through disease. Emergent insecticide resistance and environmental concerns have recently driven increased interest in biological control approaches for the management of vector mosquito populations. Copepods have been particularly successful biocontrol agents for mosquitoes. However, the efficacy of biological control agents is mediated by context-dependencies, which are often poorly understood. A functional response (FR) approach is frequently used to derive per capita ecological impacts of biocontrol agents towards target organisms, and can be applied to quantify context-dependencies of interaction strengths. However, the use of FRs alone fails to account for population-level effects (i.e. Numerical Response, NR).This study examines the efficacy of multiple biocontrol agents towards vectorially-important mosquito species, whilst explicitly considering the effects of environmental context. I develop a novel metric to quantify and compare biocontrol agent impacts under context-dependencies, Relative Control Potential (RCP), which blends per capita (FR) and population-level (NR proxies) impacts. I demonstrate that RCP can integrate environmental contexts that mediate consumer-resource interactions, such as climatic warming, which can drive interspecific differences between biocontrol agents. I establish that both predatory cyclopoid and calanoid copepods typically exhibit a Type II FR irrespective of abiotic contexts (temperature, habitat complexity, water clarity), and thus propose their efficacy in supressing mosquito populations is robust to different aquatic environments where mosquitoes breed.
Copepod-mosquito interaction strengths increased concurrently with temperature, v suggesting that offtake rates may keep pace with greater mosquito proliferations anticipated under climatic warming. Maximum feeding rates of cyclopoid copepods were unaffected by habitat complexity, and FRs were not impacted by water clarity regime shifts. This suggests that copepods are reliant on hydromechanical rather than visual cues in detecting mosquito prey. However, the presence of alternative prey resulted in species-specific shifts in FR magnitude and form in cyclopoid copepods. Whilst Culex mosquitoes avoided copepods when selecting oviposition sites, the application of domestic pond dye created an attractant, where oviposition in predator-treated water was favoured.
As predation by copepods was unaffected by dyed environments, the use of pond dye and predators in combination could promote population sink effects. I also propose the use of calanoid copepods in vector control for the first time, and demonstrate their efficacy in field-based trials that target container-based aquatic environments where vector mosquitoes breed. Finally, I demonstrate that the stocking of invasive mosquitofish can impact the overall biotic resistance of communities towards mosquito prey through interguild predation, coupled by naïveté that is often prevalent in previously fishless aquatic ecosystems. Intermediate mosquito predators were naïve to mosquitofish cues, and mosquitofish actively killed such trophic groups.
Therefore, I suggest that the use of non-native biocontrol agents should be avoided, and instead that practitioners should apply native organisms for the biocontrol of mosquito populations. This work demonstrates (1) the utility of FRs in determining interaction strengths of biocontrol agents and target organisms under context-dependencies; (2) a metric which can be used to predict and compare the impacts of potential biocontrol agents based on per capita and population-level impacts; (3) that both cyclopoid and calanoid copepods exhibit high predatory potential towards mosquito prey, which is often context-independent.
| Date of Award | Dec 2019 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Jaimie Thomas Allan Dick (Supervisor) & Neil Reid (Supervisor) |