Kaindoa, E. W. W. | Search bioRxiv

bioRxiv2025

Persistence of residual Anopheles gambiae populations associated with frontier human settlements and nocturnal livelihood-related activities at the fringes of a large conservation area in southern Tanzania

Following the rapid scale-up of long-lasting insecticidal nets (LLINs) in 2008 across the Kilombero Valley of southern Tanzania, Anopheles gambiae Giles, a highly efficient and human-specialized malaria vector, essentially disappeared within two years and has rarely been detected since. However, an ecological study of its sibling species within the An. gambiae complex, namely An. arabiensis Patton and An. quadriannulatus Theobald, in an area spanning human settlements and conserved wilderness, nevertheless detected sparse, highly focal populations of An. gambiae. Out of 4,704 An. gambiae complex specimens collected, only 10 were identified as nominate An. gambiae by polymerase chain reaction. Seven of these were captured at three surveyed fishing camps inside a Wildlife Management Area (WMA), while none were caught in five established villages west of the WMA or the national park to the east. Two of the other three were found among scattered farming settlements along the edge of the WMA. The final individual was caught in a near-natural area deep inside the WMA, but even this site was near small transient homesteads. Poisson regression modelling confirmed that capture rates at fishing camps were higher than in the peripheral settlements (Relative Rate [RR] [95% Confidence Interval (CI)] = 0.088 [0.011, 0.695], P = 0.021) or conserved natural areas (RR [95% CI] = 0.043 [0.003, 0.495], P = 0.012). Conservative estimates put the mean standing populations at each of the three fishing camps between 26 and 41 females per settlement. The absence of An. gambiae from well-conserved areas without resident humans aligns with its anthropophagic nature and dependency on human hosts. Residual An. gambiae populations persisting among frontier communities appear linked to locally common, livelihood-related nocturnal activities that preclude the practical use of LLINs, specifically fishing and guarding crops against wildlife. The continued presence of this previously important species in these ecological niches, where local livelihoods apparently undermine high LLIN coverage, shows persistence under sustained, partial insecticide pressure. This could lead to the re-emergence of this vector through the gradual evolution of resistance. However, their sparse and focal distribution suggests that new supplementary interventions, such as transfluthrin emanators, might effectively eliminate these remaining refuge populations.

ecology↗

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.

ecology↗