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Female mosquitoes can transmit pathogens to their host during blood feeding and are an important vector of human diseases such as dengue, chikungunya, filariasis and malaria. After 15 years of decline in the number of fatal malaria cases, this decline came to a halt in 2016. Growing resistance against drugs and insecticides pose a serious threat for future human health.
This thesis focuses on the behaviour of host-seeking malaria mosquitoes by analysing their flight paths during their approach to different host cues. Fundamental knowledge on the role of selected host cues was acquired. In addition, studies to support successful implementation of vector control interventions were performed in both wind-tunnel settings and the semi-field in Kenya. My research demonstrates that automated tracking systems can strengthen behavioural-ecological studies on disease vectors, in addition to conventional bio-assays such as olfactometers, by providing detailed information on the approach behaviour of mosquitoes to different targets.
The attraction towards the host-sensory cue CO2 was investigated in an olfactometer bioassay. Trap catches of female Anopheles gambiae s.s. were enhanced by separation of the CO2 source from the source of human skin emanations. Close-range deterrent effects of CO2 were overcome by the simultaneous presence of skin emanations. Flight path analysis of mosquitoes in a wind tunnel, showed that exposure to human odour resulted in prolonged and highly convoluted flight tracks. The combination of odour with heat was crucial to induce landings of host-seeking mosquitoes. A semi-field study in Kenya revealed that house-entering mosquitoes approached the eave of a house in a wide angle to the house at eave level, where the proportion that entered uninterruptedly (23%) spent just a few seconds around the eave area. The presence of insecticide-treated nets inside a house did not repel mosquitoes as measured by the number of house entries. At close range, in a wind tunnel, free-flight exposure of mosquitoes to deltamethrin-treated nets in combination with human odour did not reveal any (excito-) repellent effect and resulted in lower mortality rates compared to standard bioassays where contact with the treated material is enforced.
The knowledge obtained on the behavioural responses of mosquitoes to host cues has indirectly affected vector control tool implementations in the field. For example, in the development of an odour-baited trap, a CO2 release pipe was included that is separated from the attractive odour plume. The role of heat was exploited in the development of a repellent bioassay and a heat source was added to another trap model. Insights in house-entry behaviour and mosquito responses to bed nets support the successful implementation of push-pull systems, installation of eave tubes or implementing house improvement operations to reduce malaria transmission. An integrated vector management approach is required to further develop existing control tools by adding and improving alternative intervention techniques.
|Qualification||Doctor of Philosophy|
|Award date||23 May 2018|
|Place of Publication||Wageningen|
|Publication status||Published - 2018|