Over the past two decades efforts to control malaria have halved the number of cases globally, yet burdens remain high in much of Africa and the elimination of malaria has not been achieved even in areas where extreme reductions have been sustained, such as South Africa1,2. Studies seeking to understand the paradoxical persistence of malaria in areas in which surface water is absent for 3–8 months of the year have suggested that some species of Anopheles mosquito use long-distance migration3. Here we confirm this hypothesis through aerial sampling of mosquitoes at 40–290 m above ground level and provide—to our knowledge—the first evidence of windborne migration of African malaria vectors, and consequently of the pathogens that they transmit. Ten species, including the primary malaria vector Anopheles coluzzii, were identified among 235 anopheline mosquitoes that were captured during 617 nocturnal aerial collections in the Sahel of Mali. Notably, females accounted for more than 80% of all of the mosquitoes that we collected. Of these, 90% had taken a blood meal before their migration, which implies that pathogens are probably transported over long distances by migrating females. The likelihood of capturing Anopheles species increased with altitude (the height of the sampling panel above ground level) and during the wet seasons, but variation between years and localities was minimal. Simulated trajectories of mosquito flights indicated that there would be mean nightly displacements of up to 300 km for 9-h flight durations. Annually, the estimated numbers of mosquitoes at altitude that cross a 100-km line perpendicular to the prevailing wind direction included 81,000 Anopheles gambiae sensu stricto, 6 million A. coluzzii and 44 million Anopheles squamosus. These results provide compelling evidence that millions of malaria vectors that have previously fed on blood frequently migrate over hundreds of kilometres, and thus almost certainly spread malaria over these distances. The successful elimination of malaria may therefore depend on whether the sources of migrant vectors can be identified and controlled. Aerial sampling in the Sahel of Mali reveals large numbers of windborne malaria mosquitoes that had recently fed on blood and could cover hundreds of kilometres in a single night.

/pdf/windborne-long-distance-migration-of-malaria-mosquitoes-in-ztxsetlyyr.pdf

Windborne long-distance migration of malaria mosquitoes in the Sahel

1. The high-altitude wind-borne migration of the diamondback moth Plutella xylostella in the U.K. in 2000 was investigated (a) by direct monitoring of insect flight by vertical-looking radar and by aerial netting, and (b) through evidence of temporal variation in P. xylostella abundance deduced from a network of light traps. 2. Migrating P. xylostella were identified by a unique combination of size and shape data derived from the continuously operating vertical-looking radar. 3. Radar-detected migratory overflights correlated significantly with associated peaks in abundance of P. xylostella estimated by catches in a U.K.-wide light trap network; however the correlation was stronger when light trap catches were lagged by 1 day. 4. The first notable catches of P. xylostella in the U.K. occurred in early May, and were accompanied by migrations over the radar from the east. 5. Radar data and back-tracking indicated that a major wind-borne migration of P. xylostella from The Netherlands to southern England took place in early May, and that this was responsible for the establishment of the U.K. population. 6. The origin of early-season P. xylostella occurring in Britain is discussed.

High-altitude migration of the diamondback moth Plutella xylostella to the U.K.: a study using radar, aerial netting, and ground trapping.

Japanese encephalitis (JE) virus has a great propensity to spread, expanding its range through much of southeastern Asia in the past four decades (Umenai et al. 1985; Burke and Leake 1988; Vaughn and Hoke 1992; Monath and Heinz 1996). In the 1990s, JE spread into southern Pakistan (Igarashi et al. 1994) and to Haryana State (Prasad et al. 1993) and Kerala State (Dhanda et al. 1997) in northwestern and southwestern India, respectively. In the east, JE has invaded the eastern Indonesian archipelago, New Guinea, and the Torres Strait of northern Australia (Hanna et al. 1996b; Mackenzie et al. 1997a). The eastward spread of JE from the Oriental to the Australasian zoogeographic region and the threat this poses to the Pacific is the focus of this chapter. It is also interesting to note that there are also certain parallels in the emergence of JE in the Australasian region with the recent emergence of West Nile (WN) virus in North America, and particularly the emergence of the two viruses in novel zoogeographic regions.

/pdf/japanese-encephalitis-as-an-emerging-virus-the-emergence-and-486tn974jc.pdf

Japanese encephalitis as an emerging virus: the emergence and spread of Japanese encephalitis virus in Australasia.

Day and night sampling of windborne arthropods at a height of 200 m above ground was undertaken at Cardington, Bedfordshire, UK, during July 1999, 2000 and 2002, using a net supported by a tethered balloon. The results from this study are compared with those from the classic aerial sampling programmes carried out by Hardy, Freeman and colleagues over the UK and North Sea in the 1930s. In the present study, aerial netting was undertaken at night as well as daytime, and so the diel periodicity of migration could be investigated, and comparisons made with the results from Lewis and Taylor’s extensive survey of flight periodicity near ground level. In some taxa with day-time emigration, quite large populations could continue in high-altitude flight after dark, perhaps to a previously underrated extent, and this would greatly increase their potential migratory range. Any trend towards increases in night temperatures, associated with global warming, would facilitate movements of this type in the UK. Observations on the windborne migration of a variety of species, particularly those of economic significance or of radar-detectable size, are briefly discussed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0007485304000148

An aerial netting study of insects migrating at high altitude over England.

After Japanese encephalitis (JE) virus emerged in the Torres Strait in Australia in 1995, investigations were initiated into the origin of the incursion. New Guinea was considered the most likely source, given its proximity to islands of the Torres Strait. Almost 400,000 adult mosquitoes were processed for virus isolation from 26 locations in the Western Province of Papua New Guinea (PNG) between February 1996 and February 1998, yielding three isolates of JE virus. Two isolates of Murray Valley encephalitis, 17 isolates of Sindbis, and 1 each of Sepik and Ross River viruses were also obtained. Nucleic acid sequences of the PNG JE isolates were determined in the prM region, and in a region overlapping a part of the fifth nonstructural protein and the 3' untranslated region. The PNG isolates belonged to genotype II, and shared > 99.2% identity with isolates from humans and mosquitoes from the Torres Strait, suggesting that PNG is the source of incursions of JE virus into Australia.

Isolation of Japanese encephalitis virus from mosquitoes (Diptera: Culicidae) collected in the Western Province of Papua New Guinea, 1997-1998.

D . R . R E Y N O L D S , ' A . D . S M I T H , ' S . M U K H O P A D H Y A Y , * A . K . C H O W D H U R Y , 2 B . K . DE,2 P. S . N A T H , 2 S . K . M O N D A L , 3 B . K . D A S 3 and SUJATA M U K H O P A D H Y A Y 2 'Natural Resources Institute, Radar Entomology Unit, Malvern, U.K., ZDepartment of Plant Pathology and 'Department of Entomology, Bidhan Chandra Krishi Viswavidyalaya (BCKV), Kalyani 74 1-235, West Bengal, India

Atmospheric transport of mosquitoes in northeast India.

This paper describes the use of a kytoon-supported net to sample the insect fauna flying at about 150 m above a site in West Bengal, India. The sampling took place during four periods of the year: March, May, October and November. Amongst the insects captured were some economically important rice pests (Nilaparvata lugens, Sogatella furcifera, Nephotettix spp. and Cnaphalocrocis medinalis), some of their natural enemies, and also pest aphids (e.g. Lipaphis erysimi, Aphis gossypii and Rhopalosiphum rufiabdominalis). We found thatinsectaerialdensities aloftoften remained high untillate in the night, and we deduced from this that migration over distances of tens, or even hundreds of kilometres was in progress-movements which would lead to redistribution of both pest and beneficial insects over large areas of northeast India. Differences between aerialdensities and migration rates found for the 4 months are interpreted in terms of seasonal cropping patterns and weather, and aerial densities of N. lugens, C. m...

Seasonal variation in the windborne movement of insect pests over northeast India.

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Atmospheric transport of mosquitoes in northeast India.

Seasonal variation in the windborne movement of insect pests over northeast India.