The importance of a mosquito species as a vector of human disease is determined by multiple parameters including the human blood index (HBI). The HBI is the proportion of blood-fed, resting mosquitoes that contain human blood in their stomachs compared to the total number of mosquitoes which feed on any host species
. Accurate estimates of the HBI for a species depends on collecting an unbiased sample of resting, blood-fed mosquitoes of that species
. For highly endophilic species that rest for prolonged periods inside houses, it is relatively easy and straightforward to collect large numbers of engorged mosquitoes inside houses. However, HBI estimates based solely on collections of indoor-resting mosquitoes, even for endophilic mosquitoes, are biased towards human-fed mosquitoes, as such collections ignore the portion of the population that will have fed outdoors and be more likely to have fed on other available host species. Accurate HBI estimates require unbiased samples of the entire mosquito population that has recently fed (i.e., those that feed and rest inside houses as well as those that feed and rest outside).
Exophilic mosquito species are common throughout the malaria-endemic world
[3–5]. For exophilic vectors, capturing an adequate and representative sample of blood-fed specimens is even more challenging as they tend to be dispersed over large areas and utilize a large number of potential resting sites. The challenge is magnified when the number of adult vectors is limited, as finding engorged resting mosquitoes outdoors requires considerable time and effort to acquire even a small sample of blood-fed mosquitoes
. To enhance the prospects of finding blood-fed mosquitoes outside houses, artificial resting sites, such as clay pots and resting boxes may be provided or pits dug to attract engorged females
. However, artificial resting sites may harbour relatively few blood-fed, resting mosquitoes since the artificial sites provided must compete with the greater number of available natural resting sites
In response to biases associated with sampling blood-fed, resting mosquitoes, a novel sampling tool was designed based on a hypothesis that engorged mosquitoes might be intercepted and captured when transiting between blood feeding and resting sites. This hypothesis was based on observations by Giglioli
 and Gillies and Wilkes
 about the flight patterns of anophelines. Giglioli
 reported that Anopheles melas entered villages in corridors and at altitudes less than five feet (1.53 m) and that their flight could be diverted by fences. Gillies and Wilkes
 confirmed that most mosquitoes fly at low altitudes when crossing open terrain although anophelines will modify the height of their flight when they encounter obstacles. It followed that obstacles could be constructed, not to divert flying mosquitoes, but to impede their flight sufficiently to allow capture. For blood-laden mosquitoes, any structure encountered between the host and sites for resting might be sufficient to provide a temporary rest stop for the mosquito. Barrier screens constructed of durable mesh material (shade cloth) are inexpensive, easily constructed, and easily searched for resting mosquitoes from which they can be collected. As an artificially constructed resting site or flight barrier, a screen provides an additional significant advantage over a solid structure in that the mesh is permeable and would permit mosquitoes to follow both visual and olfactory cues to sources of blood meals, oviposition and resting sites. Upon encountering the barrier screen, mosquitoes might then stop, thereby facilitating their discovery and capture. Placement of a barrier screen between likely oviposition/resting sites and potential blood meal sources would enable the capture of both blood-fed mosquitoes seeking a resting site to develop their eggs, as well as recently emerged mosquitoes that have completed egg-laying and/or are searching for a blood meal. Comparisons of blood meal, parity and gravid status of mosquitoes captured on each side of such a screen would provide insight into directional and temporal behaviour patterns.
This initial evaluation of barrier screens as a novel sampling tool to collect exophilic mosquitoes was conducted in three countries in the southwest Pacific (Indonesia, the Solomon Islands and Papua New Guinea). The current paper presents the results of pilot studies to optimise the use and placement of barrier screens and to describe the physiological state of the mosquitoes captured. In this region the primary malaria and lymphatic filariasis vectors are exophilic, including An. sundaicus, An. vagus, An. kochi, An.s annularis, An. tessellatus and the members of the An. punctulatus group
[3, 11, 12]. Previous HBI estimates for the An. punctulatus group required years of effort to collect a sufficient number of blood-fed, resting specimens for blood source identification. This was primarily due to the difficulty of finding mosquitoes resting amongst the thick vegetation that serve as the usual resting sites for these mosquitoes
[6, 13]. Thus, only a limited number of studies have documented the host blood meal sources in the members of this group in the Solomon Islands
[14–16] and Papua New Guinea
[13, 16–22], the most recent of which was published 16 years ago.