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Title: Wolbachia in bedbugs Cimex lectularius
Author: Heaton, Louise L.
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2013
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The global rise in numbers of bedbug infestations has been facilitated by increased global travel and climate change, and further compounded by widespread pesticide resistance. The resurgence of this blood-sucking pest is costing the hospitality industry millions of pounds each year and non-chemical control strategies are urgently needed. The recent discovery that bedbugs rely on symbiotic Wolbachia bacteria for the B vitamins necessary for normal egg production, growth and development, has highlighted a possible biocontrol strategy through reducing Wolbachia infection loads. The aim of my thesis is to better understand the nature of the Wolbachia-bedbug symbiosis and the mechanisms by which Wolbachia achieve effects in their host in order to determine whether such biocontrol strategies are likely to succeed. I develop protocols to manipulate Wolbachia infection loads using heat or antibiotic treatment to test hypotheses relating to (i) the fitness effects of Wolbachia infection for male hosts; (ii) the fitness effects of Wolbachia infection for female hosts and (iii) the underlying mechanisms through which Wolbachia achieve their effects. My research has revealed that Wolbachia increase the fitness of both male and female hosts via a range of mechanisms. The male's Wolbachia increase the male host's fitness through increasing the egg laying rate of the female he has mated with. I found no evidence that Wolbachia are transferred in the male's ejaculate. Wolbachia may affect egg laying rate through raising the quality of the male's ejaculate, such as via direct nutritional provisioning or by enabling the male to invest in a higher quality ejaculate. Another symbiont in male bedbugs may also influence ejaculate production. Wolbachia increase the female host's fitness by increasing her egg hatch and development success (proportion of eggs that hatched or reached adulthood), increasing offspring body size (which will increase her indirect fitness by increasing the fitness of her offspring) and reducing the fitness costs (wounding and infection) associated with traumatic insemination. This latter effect was associated with an enhanced melanisation response. Despite the widespread fitness benefits that Wolbachia provide to both male and female hosts, biocontrol methods involving a reduction in Wolbachia loads in natural bedbug populations are unlikely to be effective. (i) It is not possible to reduce the Wolbachia load (population size) of all individuals in a bedbug infestation due to the logistical difficulties in administering antibiotic treatment. Heat treatment to reduce Wolbachia loads is logistically feasible but does not present an effective alternative to antibiotics, as the reduction in bedbug fitness is too subtle (even though significant) and short-lived. (ii) A reduction in Wolbachia load does not kill the bedbugs outright, so infestations will remain after biocontrol has taken place. (iii) The ecology of bedbugs precludes the release of sterile males - a biocontrol strategy used for other pest insects -as a biocontrol strategy for this system.
Supervisor: Siva-Jothy, Michael T. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available