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Title: Insect-plant interaction in the cowpea beetle, Callosobruchus maculatus
Author: Ahuchaogu, Christopher Emeka
ISNI:       0000 0004 7970 2370
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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The cowpea weevil, Callosobruchus maculatus Fab. is an economically important pest of stored grain – and especially of cowpeas - in sub-Saharan Africa. It causes serious damage to stored peas, resulting in reduced food security for subsistence farmers and financial loss and economic uncertainty to larger-scale farmers. Due to the economic and nutritional importance of the crop, particularly in Nigeria, farmers take several measures to protect their produce against insect infestations. The application of pesticides has been the generic control measure due to its effectiveness, affordability and ease of application. However, the negative effects of this control strategy - including increasingly apparent health and environmental consequences – is increasingly motivating stakeholders to advocate for an alternative management approach that has less social and environmental impact and is more sustainable. In this thesis, I investigate C. maculatus biology in the context of its interaction with its primary food source, Vigna unguiculata L. Walp. (the cowpea). I start by examining the sensory anatomy of the antenna and female external genitalia comparing individuals from a lab-adapted strain (widely used as a model system in evolutionary biology) and a wild strain. I then examine the pest's ability to detect host odour from the peas (the stored product) and the living pods (an as yet understudied aspect of the pest's infestation tactics) based on understanding olfactory cues. I also analyse volatile samples from the host plant to identify candidate attractants. The beetle is known to be plastic in its choice of host, so I finish the study by examining the nature of that plasticity in lab and field strains as well as measuring the life-history consequences of those choices. My results document antenna sensilla types and show that gross antenna morphology does not differ between sex or strain. However, I detected sexual dimorphism in the density of specific antennal sensilla: The antenna of males has more olfactory sensilla, whereas females have more of contact-chemosensory sensilla. In terms of their behaviour, insects were attracted to mature bean pods (compared to developing pods). Interestingly, the wild strain differed from the lab-adapted strain in several key lifehistory parameters: although females from both strains showed a preference for particular host types as an oviposition substrate, there was no apparent adaptive correlation between their choice of host and the life-history performance of the progeny. These results represent the first steps in developing and designing new, more integrated management strategies that focus on key life-history, behavioural and environmental bottlenecks in the pest's biology that will enable farmers to leverage more sustainable and effective control methods.
Supervisor: Siva-Jothy, Michael T. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available