Biology subjects

Duggan, L. M.

Publications and source records attributed to Duggan, L. M..

4 recordsLinked to original sources

bioRxiv2024

Comparative attractiveness of Anopheles quadriannulatus and Anopheles arabiensis to humans estimated by comparing the relative abundance of these two species in larval samples, unbaited adult catches and human-baited adult catches.

Understanding mosquito vector behaviour, abundance, and bionomics is crucial for effective malaria prevention. Since most malaria parasites in humans are strict anthroponoses, mosquito preference for humans as a blood source is a key determinant of transmission intensity and intervention strategies. This study compares the attraction of Anopheles arabiensis and Anopheles quadriannulatus to humans by assessing their relative abundance in larval samples and adult mosquito catches using unbaited and human-baited traps. The research investigated how the abundance of these sibling species varies with the local availability of humans, livestock, and wildlife as potential blood sources. Surveys of larval and adult mosquito populations were conducted at 40 mobile camping locations distributed across a landscape mosaic of different habitat types, with a gradient of land use practices ranging from comprehensive conversion to agriculture and human settlement to essentially intact natural ecosystems inside well-protected conservation areas. Larvae were collected from all accessible water bodies within a 2 km radius of each mobile camp, while adults were surveyed using four light traps and one interception netting barrier trap at each camp. Light traps were strategically placed at locations such as beside a human-occupied tent, near the camp, in a nearby streambed, and in an open natural glade, while the netting barrier trap was placed in the open natural glade. Most adult Anopheles gambiae complex mosquitoes caught were unfed and presumably host-seeking. The mean catches of the complex in light traps next to the human-occupied tent was over four times higher than elsewhere around the camp (p<<0.0001). Catches decreased with distance from humans, suggesting attraction to humans by at least one species in the complex. An. arabiensis was caught in greater numbers in the human-occupied tent, while An. quadriannulatus catches remained consistently low across all traps, even in wild areas where it was dominant in larval population. The proportion of An. arabiensis in adult collections was higher than in larval samples (98.7% versus. 78.3%, p<<0.0001), and adults caught beside human-occupied tents had 36 times higher odds of being An. arabiensis rather than An. quadriannulatus. Similarly, the barrier trap away from humans but frequently visited by researchers showed a 24-fold enrichment of An. arabiensis. These results confirm the strong attraction of An. arabiensis to humans, contrasting with the non-vector An. quadriannulatus, which is largely unresponsive to humans. Light traps by human-occupied tents efficiently capture anthropophagic mosquitoes outdoors, while unbaited traps far from people appear to give unbiased representations of larval population composition but with very low efficiency. Moreover, netting barriers with human activity attract anthropophagic mosquitoes, turning them into semi-baited traps with moderate efficiency.

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bioRxiv2024

Blood host preferences and competitive inter-species dynamics within an African malaria vector species complex inferred from signs of animal activity around aquatic larval habitats.

The dual-specialized behavioural adaptions of Anopheles arabiensis, to feed readily upon either people or cattle, enable it to thrive and mediate persistent residual malaria transmission across much of Africa, despite widespread use of long-lasting insecticidal nets (LLINs). Indeed, LLIN scale up has often resulted in it dominating the more efficient but vulnerable malaria vector Anopheles gambiae, its sibling species within a complex of the latter name. However, the feeding behaviours and competitive relationships of An. arabiensis with other sibling species in well conserved natural ecosystems, where its known preferred hosts are scarce or absent, remain largely unexplored. Potential aquatic habitats were surveyed for An. gambiae complex larvae across a gradient of natural ecosystem integrity in southern Tanzania, encompassing fully domesticated human settlements, a partially encroached Wildlife Management Area (WMA), and well conserved areas of the recently gazetted Nyerere National Park (NNP) before substantive development of tourist access or accommodation. Direct observations, tracks, spoor and other signs of human, livestock or wild animal activity around these water bodies were recorded as indirect indicators of potential blood source availability. While only An. arabiensis was found in fully domesticated ecosystems, its non-vector sibling species An. quadriannulatus occurred in conserved areas and dominated the most intact natural ecosystems. Proportions of larvae identified as An. arabiensis were positively associated with human and/or cattle activity and negatively associated with distance inside NNP and away from human settlements. Proportions of An. quadriannulatus were positively associated with activities of impala and bushpig, implicating both as likely preferred blood hosts. While abundant impala and lack of humans or cattle in intact acacia savannah within NNP apparently allowed it to dominate An. arabiensis, presence of bushpig seemed to provide it with a foothold in miombo woodlands of the WMA, despite encroachment by people and livestock. While this antelope and suid are essentially unrelated, both are non- migratory residents of small home ranges with perennial surface water, representing preferred hosts for An. quadriannulatus that are widespread across extensive natural ecosystems all year round. Despite dominance of An. quadriannulatus in well-conserved areas, An. arabiensis was even found in absolutely intact environments >40km inside NNP, suggesting it can survive on blood from one or more unidentified wild species. While self-sustaining refuge populations of An. arabiensis inside conservation areas, supported by wild blood hosts that are fundamentally beyond the reach of insecticidal interventions targeted at humans or their livestock, may confound efforts to eliminate this key malaria vector, they might also enable insecticide resistance management strategies that could restore the effectiveness of pyrethroids in particular.

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bioRxiv2024

An effective model for community-based conservation around authorized fishing settlements inside a devolved Wildlife Management Area in southern Tanzania

Wildlife Management Areas (WMAs) represent a relatively new institutional model for devolved, locally-led conservation in Tanzania, in which local villages set aside part of their land for wildlife conservation and manage that resource collectively, so that their stakeholder communities can collectively leverage economic and social benefits from income-generating activities like tourism. This study examines the relationship between community-defined land use plans and de facto land use practices, and the influence of the latter on the relative abundance and distribution of large wild mammals in a across the Ifakara-Lupiro-Mangula (ILUMA) WMA, which acts as a key buffer zone between Nyerere National Park (NNP) to the east and adjacent stakeholder villages to the north and west. All observed signs of wildlife and human activity were recorded across 32 locations inside ILUMA and in the permanent settlements and national park that respectively border it to the west and east. Across much of ILUMA WMA, in areas where agreed land use plans were not adhered to, rampant cattle herding and land clearing for agriculture were associated with reductions in wildlife richness and biodiversity, as well as overall ecosystem integrity. Although human settlement was also generally associated with reduced natural ecosystem integrity, some important exceptions to this rule illustrate how sustainable livelihoods for local people that are based on well-managed natural resource harvesting practices may actually enhance conservation effectiveness: Three authorised human settlements within the WMA, where fishing was the primary permitted livelihood and local communities collaborated with the WMA management, were surrounded by pristine land cover with thriving terrestrial wildlife populations. Correspondingly, the best conserved parts of the WMA not only included those closest to the boundary with the national park to the east, but also these fishing villages along the riverbank to the north, where compliance with agreed land use plans was most rigorous. Overall, this study documents a useful example of how a devolved conservation area may conditionally host resident local communities undertaking selective natural resource extraction activities and collaborate with them to achieve effective de facto conservation practices.

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bioRxiv2024

A self-cooling self-humidifying mosquito carrier backpack for transporting live adult mosquitoes on foot over long distances under challenging field conditions.

It is often necessary to use motorized transport to move live mosquitoes from distant field collection points into a central insectary, so that their behavioural and/or physiological phenotypes can be assessed under carefully controlled conditions. However, a survey of heritable insecticide susceptibility traits among wild-caught Anopheles arabiensis mosquitoes, collected across an extensive study area composed largely of wilderness in southern Tanzania, necessitated that live mosquitoes were carried on foot over distances up to 25 km per day because most of the area was impassable by car, motorcycle or even bicycle during the rains. A self-cooling, self-humidifying carrier backpack was therefore developed that allows live adult mosquito specimens to be transported across rugged miombo woodland and floodplain terrain throughout the year. This wettable backpack was fabricated from stitched Tanzanian kitenge cotton fabric and PVC-coated fiberglass netting that allows easy circulation of air in and out. An outer cover flap made of cotton towelling embedded inside a kitenge envelope overhangs the fiberglass netting upper body of the bag, to protect mosquitoes from direct sunlight, and can be soaked with water to maintain low temperature and high humidity inside. Mean survival of insectary-reared female Anopheles arabiensis transported through 9 different mobile camps inside the 509 km2 Ifakara-Lupiro-Mangula Wildlife Management Area (ILUMA WMA), over up to 143km and 25 days, was indistinguishable from those left in the field insectary over the same period. Although considerable variance was observed between different batches of mosquitoes from the insectary and between individual cups of mosquitoes, the different levels and positions inside the backpack had no influence on survival. Temperature and humidity inside the backpack were maintained at standard insectary condition throughout, despite much more extreme conditions immediately outside. When the backpack was applied to collecting wild An. arabiensis and Anopheles quadriannulatus across a much larger study area of >4000 km2, encompassing the ILUMA WMA, some nearby villages and adjacent parts of Nyerere National Park (NNP), it achieved a mean survival rate of 58.2% [95% confidence interval 47.5 to 68.2]. Encouragingly, no difference in survival was observed between ILUMA WMA and NNP even though transport back from NNP involves much longer distances, sometimes involving lengthy journeys by car or boat. Overall, this mosquito carrier backpack prototype appears to represent a viable and effective method for transporting live wild-caught mosquitoes on foot across otherwise impassable terrain under challenging weather conditions with minimal detrimental impact on their survival.

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